I

Government of Karnataka

KARNATAKA TEXT BOOK SOCIETY (R)100 Feet Ring Road, Banashankari, 3rd stage,

Bengaluru-85

SCIENCE

8EIGHTH STANDARD

2015

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PREfACE

The Textbook Society, Karnataka has been engaged in producing new textbooks according to the new syllabi prepared which in turn are designed based on NCF – 2005 since June 2010. Textbooks are prepared in 11 languages, seven of them serve as the media of instruction. From standard 1 to 4 there is the EVS and 5th to 10th there are three core subjects namely mathematics, science and social science.

NCF – 2005 has a number of special features and they are:

• Connectingknowledgetolifeactivities

• Learningtoshiftfromrotemethods

• Enrichingthecurriculumbeyondtextbooks

• Learningexperiencesfortheconstructionofknowledge

• Making examinations flexible and integrating them with classroom experiences

• Caringconcernswithinthedemocraticpolicyofthecountry

• Makeeducationrelevanttothepresentandfutureneeds.

• Softening the subject boundaries integrated knowledge and the joy of learning.

• Thechildistheconstructorofknowledge

The new books are produced based on three fundamental approaches namely.

Constructive approach, Spiral Approach and Integrated approach

The learner is encouraged to think, engage in activities, masters skills and competecies. The materials presented in these books are integrated with values. The new books are not examination oriented in their nature. On the other hand they help the learner in the total development of his/her personality, thus help him/her become a healthy member of a healthy society and a productive citizen of this great country India.

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Nagendra KumarManagingDirector

Karnataka Textbook Society®Bengaluru, Karnataka.

Prof. G S MudambadithayaCoordinator

Curriculum Revision and Textbook Preparation Karnataka Textbook Society®

Bengaluru, Karnataka

We live in an age of science and technology. During the pastfivedecadesmanhasachievedgreatthingsandrealizedhisdreamsand reached pinnacle of glory. He has produced everything to make life comfortable. In the same way he has given himself to pleasures and reached the stage in which he seems to have forgotten basic sciences. We hope that at least a good number of young learners take to science in higher studies and become leading scientists and contribute their share to the existing stock of knowledge in order to make life prosperous.

Ample opportunity has been given to learners to think, read, discuss and learn on their own with very little help from teachers. Learning is expected to be activity centeredwith the learners doingexperiments, assignments and projects.

The Textbook Society expresses grateful thanks to the chairpersons,writers, scrutinisers, artists, staff ofDIETs andCTEsand the members of the Editorial Board and printers in helping the Text Book Society in producing these textbooks.

Bengaluru

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fOREWORD

The Present text book for eight standard science has been prepared according to the NCF 2005. The revised syllabus approved by the authorities concerned has been followed.

The main feature of the text book is constructive approach. The activity based

development of the content may help in the formation of concepts. In some areas thereisanarrativeapproachonaccountofthenatureofthesubjectmatter.Directdefinitionsinsomeareasaredeliberatelyavoidedsuchthatthelearnercandrawhisown but correct conclusions. Learning to learn principle is followed by and large.

The text book committee is presenting this text book with pleasure and with

a bit of anxiety. Extreme care is taken to avoid content errors. However, lack of sufficient information or elaboration in certain units should not be construed aswrong information. This is done to avoid memorization of facts and to reduce the burden.

It should be noted that the main aim of secondary education is to lay the foundation for higher education. It is a cushion for children to jump to higher studies and to develop their personality by meeting their immediate instinctive needs. Learneratthisstage,shoulddevelopminimumskillsandshouldacquiresufficientknowledge so that he can interact with his present environment effectively.

We, the Chairpersons of text book preparation committee, express our sincere thanks to prof. G.S. Mudambadithaya, coordinator for assigning this responsibility to us. We also wish to express our thanks to writers, scrutinisers, editorial committee members, teachers and translators for their valuable contributions in improvingthequalityofthecontent.Ourthanksarealsoduetotheartistforhis drawingsandtotheauthoritiesofKarnatakaTextbookSocietyandDSERTfortheirkind cooperation.

Any further feasible suggestions to improve the text book are welcome, Humans are never perfect. But perfection is the goal towards which one should sincerely try to move.

Chairpersons Dr. T.A. Balakrishna Adiga

A.B. Katti

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Text Book Committee

Chairpersons Dr. T.A. Balakrishna Adiga, Principal, Silicon city, P.U.College, Bengaluru.

Sri. A.B. Katti, Rtd.HeadMaster,SheshadripuramHighschool,Bengaluru.

Members Smt. H.V. Bhagyalakshmi, Rtd.ScienceTeacher,StellaMary'sHighSchool,

Bengaluru.

Sri. H.L. Satheesh,TGTinScience,DemonstrationSchool,RIE,Mysuru.

Sri. G. Satish, Assistant Teacher, R.V. Girls High School, Jayanagar , Bengaluru.

Sri. Venkatesh Udupa, Assistant Teacher, Viveka P.U. College, Kota, Udupi.

Sri. M.G. Manjunatha, Assistant Teacher, S.J.S. R.R. High School, Yalavatti, Shivamogga.

Sri. Girish Kadlewad,AssistantTeacher,Govt.HighSchool,Martoor,Kalaburagi.

Sri. Lakshminarayana, Artist, Drawing Teacher,Govt.High School, D.G.Halli,Bengaluru.

Scrutinisers Sri. Ragavendra Patil, Rtd.Prinicipal,ASTP.U.College,Malladihalli,Chitradurga.

Dr. C.R. Girija,Associateprofessor,SSMRVDegreeCollege,Jayanagar,Bengaluru.

Editorial Board Prof. M.R. Nagaraju, Educationist, Yalahanka Upanagara, Bengaluru.

Dr. M.J. Sundar Ram, Prof. of Biology, Surana Ind. P.U. College, Basavanagudi, Bengaluru.

Prof. H.S. Lakshminarayana Bhatta, Rtd. Prinicipal, V.V. Puram, Science College, Bengaluru.

Chief Co-ordinator Prof. G.S. Mudambadithaya, Curriculum Revision and Text book preparation,

Govt. of Karnataka.

Chief Advisors Sri. Nagendra Kumar, ManagingDirector,KarnatakaTextBookSociety,Bengaluru.

Sri. Panduranga,DeputyDirector(incharge),KarnatakaTextBookSociety,Bengaluru.

Programme Co- ordinator Smt. Bharathi,SeniorAsst.Director,KarnatakaTextBookSociety,Bengaluru.

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Chapter Number Chapter Name Page No. Number of teaching

periods required

1 Our natural resources 1-8 3

2 Study of our environment 9-22 7

3 Structure of atom 23-34 6

4 Moreaboutatoms 35-43 6

5 Study of cells 44-59 7

6 Classificationoflivingorganisms 60-73 8

7 The world of microbes 74-82 4

8 Describingmotion 83-95 4

9 Force and Newton’s laws of motion 96-106 4

10 Energy and its forms 107-117 5

11 Chemical reactions and their types 118-127 8

12 Chemicals in our daily life – 1 128-141 7

13 Chemicals in our daily life – 2 142-151 6

14 World of sounds 152-164 6

15 Heat 165-178 5

16 States of matter 179-187 7

17 Our colourful world 188-210 5

18 Food and its constituents 211-226 7

19 DigestionandRespiration 227-247 8

20 Reproduction in higher plants 248-253 8

21 Communication gadgets 254-267 5

22 Food production–soil and water management 268-285 6

23 Evolution of life 286-294 5

24 Beyond the earth 295-313 7

Index

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Chapter 1 Our Natural resOurCes

after studying this chapter students :• explainthemeaningofnaturalresources.

• statetheimportanceofnaturalresources.

• differentiatebetweenlivingandnon-livingresources.

• reasonouttheneedforconservingnon-renewableresources.

• explainthebiologicalneedofwater.

• statetheilleffectsofexcessiveuseofchemicalsinagriculture.

We see various kinds of things surrounding us. Some of themarelivingandothersarenon-living.Thethingsthatoccurinnatureandthatareusefultousarecallednatural resources.Manyofthesenaturalresourcesareessentialforoursurvival.Someofthemareusedforsatisfyingourwants.

A large number of these natural resources are either living orderivedfromlivingorganisms.Forestandwildlifeareexamplesofliving resources.Forestproductsliketimber,animalproductslikeleatheraredescribedaslivingresources.MineralfuelslikeCoalandfossilfuelslike petroleumproducts are derived from remains of decayed, deadorganismsoverlongperiodsoftime.Land,water,airandmineraloresareexamplesofnon-living resources.

Someofthenaturalresourcescangetreplacedinnatureeasily.Suchresourcesarecalledrenewable natural resources.Solarenergy,air,water,wildlife,forestsandagriculturalcropsareexamplesofrenewableresources. Some of these are continuously available for use. Foreg:solarenergyandair.Suchresourcesaredescribedasinexhaustible resources. Resources like forests andwild lifemay get depleted bycontinuous use or interference by humans.However, they can bereplenished tomaintain a flow.Hence, they are calledexhaustible resources.

Someofthenaturalresourceshavebeenformedonearthoveralongperiodoftime,evenbillionsofyears.Foreg.fossilfuelsandminerals.Therateofformationofsuchmineralsisveryslow,comparedtotherateatwhichtheyarebeingusedbyhumans.Suchresourceswhichcannotbereplenishedoncedepleted,arecallednon renewable resources.

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Letuslearnmoreaboutsomeofthesenaturalresourcesthathaveasignificantinfluenceonhumanlife.

Water

Water isauniquenaturalresource,as it isverymuchessentialfortheexistenceoflife.Itisthemostcriticallimitingfactorformanyaspectsoflifesuchasenvironmentalstability,biodiversityconservation,fuelsecurityandevenhealthcare.Inmostcases,thereisnosubstituteforwater.Themostsignificantaspectofwater is that it isa largelyirreplaceableresourceunlikeenergy,whichhasalternatives.

Innature,watermaychangeitsformbutwecanalwaysretrieveit.TheEarthholdsthesamequantityofwaterasitdidwhenitwasformed.

Youmaybeawareofthefactthatnearly71%oftheEarth’ssurfaceiscoveredbywater.ItisoneofthemostimportantcomponentsrequiredforsustaininglifeonEarth.

Nearly97%ofwateronEarth isheld inoceans,seasandotherlargewaterbodies. 0.001%ofwater occurs inatmosphereaswatervapour.About2.4%ofthewaterisfoundinglaciersandpolarice-caps.Remainingwaterisfoundinrivers,lakes,pondsandotherwaterbodies.Assuch,averysmallpercentageofthisvaluablenaturalresourceisavailableforhumanuse.

Activity 1.1

Measure 2200 ml of water into a container. Assume that 2200ml represents the total water available on earth. Take a teaspoon and measure out 12 spoonfuls of water into a small transparent container. This is the total amount of fresh water on the earth including the water found in lakes, rivers, ice-caps, and as ground water. The water that remains in the large container represents salty water. From the container with 12 spoonfuls of water, measure out two spoonfuls into a dish and remove half a spoon of water from the container which now has 10 spoonfuls of water. This represents the water found on the surface of the Earth in fresh water lakes. From the remaining water in the small container, remove one drop using an ink-dropper. This drop represents the amount of water found in rivers. The smaller container will now have about 9 spoonful of water left in it. This represents the amount stored in ice-caps. Com-pare the quantities of water in the various containers.

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Withevensuchasmallquantityofwateravailable,humanshavebeenusingwaterforvariouspurposes.Itisestimatedthattheaverageconsumptionofwaterbyahumanbeingrangesfrom20litresto30litresperday,dependingontheiractivityandplaceofliving.

Fig1.1Waterdistributiononearth

Waterisusedforvarioushumanactivitieslikedrinking,agriculturalpurposes,washingandrecreation.Inadditionwaterisusedforheatexchangeprocesses,industriesandfireextinguishers.

Thelargestuseofwateroccursintheagriculturalsector.Inourcountry,itisestimatedthatmorethan80%ofthewateravailableforhumanuse,isemployedforagriculturalpractices.InstateslikePunjab,Haryana,UttarPradeshandGujarat,over85%of irrigation isdonethroughgroundwatersources.

Do You Know?

Toproducefoodformorethan7billionpeopleinhabitingEarth,thewaterrequiredwillbeequaltofillacanal10metredeep,100metrewideandnearly7.0kmlong!Thisisenoughtocircletheglobe180times!

Wehavebeenmisusing,exploitingandpollutingwatertoagreatextent.Someoftheproblemsrelatedtowateranditsuseinourcountryarescarcity,overuseandunequaldistribution.Theannualrainfallinthe country is about 400millionhectaremetre. Another 20millionhectaremetersflowsinassurfacewater.Thisisconsideredmorethansufficienttoprovidewaterfordifferentusesinthecountry.However,overuseofwaterandlackofplanninghaveresultedinastateofscarcity.Itisnecessarytoincreaseeffortsrelatedtoconservationofwaterinbothurbanandruralareas.Importanceshouldbegiventoeducatepeopleabouttheneedforharvestingrainwaterresourcesandconstructingwatersheds.

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Activity – 1.2

Fig1.2Worldwaterday

Is overuse, scarcity and quality of water an important issue of concern in your school or locality? Find out the reasons.

Do You Know ?

March 22nd of every year is celebrated all over as World Water Day.

soilSoilisanaturalresourcethatprovides

minerals andwater to all land plants.Particularly for agricultural crops it is

a primary nutrient base. In addition, it is the place of living for awidevarietyoforganismslikeearthworms,crabs, insectsandmicroorganisms.

Soilabsorbsrainwaterandlaterreleasesthesameforusebyplants.Watergetspurifiedasitpercolatesthroughsoil.

Humanactivitieshave influencedeven thesoilquality.Wehavedeteriorated the soil quality in variousways.One such situation issalinisationofsoil.Itiscausedbyariseinthewatertable,whenwaterisaddedtosoilatahigherratethantherateatwhichitisbeingusedfromthesoil.Saltpollutiondiminishesthefertilityandinextremecasesitruinsthesoil.Waterloggingandsalinisationarethemaincausesofanotherseriousprobleminwhichoncefertile landsarebecomingbarrenanduseless.Thisiscalleddesertification.Today,thenutrientrichalluvialsoilsofPunjabsufferseriouslyfromdesertificationcausedbytheintroductionofexcessiveirrigation.

Apartfromthis,theuseofchemicalfertilizershasalsobeenaseriouscauseofsoilpollution.Theuseofpesticidestoprotectouragriculturalcropshasalsobeenaddingtothisproblem.

However,themostseriousthreattosoilistheprocessoferosion.TopSoilisgettingexposedduetoactivitieslikedeforestationandovergrazing.Asaresult,soilisbeingsubjectedtotheactionofwindandwater.Thisisleadingtoahugelossofusefultopsoil.

Youknowthatformationofsoiloccursbyanaturalprocesscalledweatheringofrocks.Therateatwhichsoilformationoccursismuchlesscomparedtotherateatwhichsoilerosiontakesplace.Thishas

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ledtoaseriousconcernaboutsoilconservation.Soilprotectionhasnowbecomeanintegralpartofanyconservationplan.Restoringthesoil quality canbe a solution formanyof the environmental issuesbotheringhumanlife.Forests

Forests are renewable natural resources that have innumerablecontributionstotheenvironment.Forestsmaintainwatercycle.Theyprovide habitat for wild animals. Forestsmaintain soil quality bypreventingsoilerosion.Forestsprovidetimberandmanyotherusefulproductsandservices.Generally,forestsareindicatorsofthenaturalwealthofanation.

However, rapid changes have been noticed in the percentagedistributionofforestsintheworld.Itisnowestimatedthatonly20%oftheworld’soriginalforestsremainintactandundestroyed.

Inthelast20to30yearstherateofdeforestationhasincreasedtosuchanextentthatwearetodayfacingseveralenvironmentalproblems.Thepatternofrainfallhaschanged,sincewatercyclehasbeenaffected.Therateofsoilerosionhasincreasedasthevegetationcoveronsoilhasbeendestroyed.Itisnownecessarytorestoretheforestsbyactivitiessuchasafforestation.

Fig1.3WorldforestDay

Do you know?

March21ofeveryyearisobservedalloverasWorldForestDay.

Think : Why do we have to observe WorldForest Day? Will observing such days reallyhelpinthecauseofenvironmentalissues?

Wildlife The termwild life is used to describe the species of plants and

animalslivinginthewild.Itrepresentsthediversityofspeciesamongorganismsinhabitingourforests,seasandoceans.Humanactivitiessuchashunting,poachingandcapturinghaveseverelyaffectedwildlife,leadingtotheextinctionofmanyvaluablespecies.Manyspeciesarefacingathreatofextinctioninthenearfuture.

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Theimmediateneedisthemeasurestobetakenfortheconservationofwild life. It isoneof the importantchallengesof thepresentandtheimmediatefuture.Effortsarebeingmadetoconservethoselivingresourcesthroughtheirmaintenanceintheirnaturalhabitats.Nationalparks,wild life sanctuaries, bird sanctuaries are examples of suchconservationmeasures. Sometimes, conservation of living resourcesinvolvesmeasureswhereinsamplepopulationsareprotectedinzoos,botanicalgardensandothermanmadesituations.Itmayalsoinvolvethecreationofseedbanks,genebanksandsimilargeneticresourcecentres.

Fossil FuelsCoal, petroleum products and natural gas represent a kind of

resource collectively called fossil fuels. They are the result of thephotosyntheticactivityof greenplants,whichwere existingmillionsofyearsago.Theygotsubmergedwithintheearth’scrustandformedthefossil fuels.Theyarenon-renewableresources. It isnotpossibletoreducetheirconsumptionwhichisveryhighandhence,weforeseetheirtotaldepletioninthenearfuture.

Coalisanaturalresourcewithhighcarboncontent.Threetypesofcoaldepositsarenormallyfound.anthraciteisoneforminwhichcarboncontentisveryhigh(about80%).lignitehasabout50to65%ofcarbon.Bituminous coalhaslessthan40%ofcarbon.

Petrol, diesel, kerosene, lubricating oils and naptha representvariousformsofpetroleumproducts.Theyaccountforabout40%ofthetotalenergyconsumedintheworld.

Naturalgasformsinthesamewayasoil.Lowsulphurcontentofnaturalgasmakesittheleastpollutivesourceoffuel.

Oncewe discovered these fossil fuels,we beganutilising themat an ever increasing rate. A total of about 227 billion barrels(1barrel=159litres)oftheseoilswereextractedfromfossilfuelsbetween1859and1969.aboutFiftypercentofthiswasextractedin100yearswhilethenextfiftypercentwasextractedinjust10years!

Todayourconsumptionrateisinexcessoftherateofformationof fossil fuels. In one daywe consumewhat the Earth has takenone thousand years to form!Hence, fossil fuels are considered asnon-renewableresources.

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Mineral resourcesAmineral is a substance that is naturally found in theEarth’s

crustandisnotformedfromlivingmatter.MineralsareformedduetoEarth’sgeologicalprocessesovermillionsofyears.Hence,mineralsarealsonon-renewableresources.

More than100minerals includingmetals likegold, iron,copperandaluminiumandnon-metalslikestone,sandandsaltareextractedandprocessedforhumanuse.Miningistheprocessofextractionandprocessing.

Mininghasbecomemoreintenseandwidespreadinrecentyears,causingseriousenvironmentaldegradation.

exercises :I. Four alternatives are given to each of the following incomplete

statement / question. Choose the right answer:1. Oneofthefollowingdoesnotbelongtothegroup

a.water b.forests

c.petrol d.soil

2. Governmenthasbannedhuntingofwildanimals.Thishelpsto

a.maintainbiodiversity b.promotetourism

c.providefoodtoanimals d.maintainsoilfertility

II. Fill in the blanks with suitable words :1. Resourcesthatgetreplenishedinnaturearecalled___________.

2. Petrol,andkeroseneare___________formsofnaturalresources.

3. Ifthereisriseinwatertable,soilbecomes___________.

4. Soilprovides___________and___________toterrestrialplants.

5. Anexampleforrenewableresourceis___________.

III. answer the following : 1. Whatarenaturalresources?

2. Differentiatebetweenrenewableandnon-renewableresources.

3. Listtheusesofwater.

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4. Whatismining?

5. Whathappensiftoomuchoffossilfuelsisused?

6. Astudentarguesthatanationwillberich,ifitsforestsareconserved.Explain.

IV. Match the following :

A B

1. highcarboncontent a. lignite

2. renewable b. bituminous

3. lowsulphurcontent c. wind

4. formationofsoil d. L.P.G.

e. weatheringofrocks

f. anthracite

g. naturalgas

“There are forces in life working for you and against you. One must distinguish the beneficial forces from the malevolent ones and choose correctly between them.”

-Abdul Kalam

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Chapter 2study OF Our eNVIrONMeNt

after studying this chapter students :• understandtheimportanceofwaterforexistenceoflife.• appreciatetheroleofwaterbodiesinmaintainingecologicalbalance.• predicttheimportanceofphotosyntheticalgaeinprimitiveearth.• appreciatetheneedofinteractionbetweenlivingorganisms.• developtheskillofmaintaininganaquarium.

earth as a unique planet

Youareawarethatearthisauniqueplanetinthesolarsystem,sinceitistheonlyplanetthatsupportslife.Whatmakestheearthtoexhibitthisfeature?Isitthepositionofourplanetinthesolarsystem?IsitthephysicalandchemicalcompositionoftheEarth,thathaveresultedfromtheinnumerableprocessesthatoccurredsinceitsformation?

TheEarthissaidtohavebeenformedabout4.8billionyearsagoandthefirstsignoflifeissaidtohaveappearedabout3.8billionyearsago.Youwilllearnmoreaboutthisinchapter23.However,itwasnotuntilabout1.4billionyearsago,thatthefirstmulticellularorganismsappeared.Theseorganismsandtheotherformsoflifewhichevolvedfromthem,couldsurvivewhentheconditionsonearthbegantostabilizegradually.

Youknowthatnearly71percentofEarth’ssurfaceiscoveredbywater.Thispartoftheearthiscalledhydrosphere.Itistheonlyplanetinthesolarsystemwithabundantliquidwaterandthisisoneofthefactorsresponsible formaking lifepossibleon theEarth.Waterhassomeuniquephysicalandchemicalproperties,whichareessentialforsupportinglife’sexistence,notseeninothersubstances.

• Water requires considerable amount of energy to get heatedupandalsotogetconvertedfromliquidstateintogaseousstate.Onaveryhotday,waterbodieshelpmaintainatmospherictemperaturecoolbyabsorbingheatfromthesun.Whenthesunsets,theheatwhichwaterhasabsorbedisreturnedtotheatmosphere,aswaterevaporates.Sucharegulation iscrucial forthesurvivalof livingorganisms.

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• Waterhasahighresistancetosuddenchangesintemperatureandthisfeaturemakeswateranexcellenthabitatformostorganisms.Infact,youmayrecallherethatprimitivelifeappearedonlyinwater.

• At40Cwaterexpandsoncoolingorheating.Thisfeatureensuresthatallthewaterinawaterbodywillbecloseto00Cbeforeanyfreezingcanoccur.

• Thehighsurfacetensionofwateranditstendencytoexpandonfreezinghelpsinweatheringofrocks,leadingtosoilformation.

Think : Isthereanyotheruniquepropertyofwaterthathassupportedtheexistenceoflife?

Yetanotheruniquefeatureofearthisitsatmospherewhichisamixtureofgases,watervapourandfinedust,surroundingtheearth.Youknowthatnearly78%ofatmosphereisnitrogenand21%isoxygen,whilecarbondioxide,argonandothergasesmakeuptherest.

Atmosphereoftheearthatitsbeginningwasrichincarbondioxideandtheoxygencontentwasveryless.Asphotosyntheticalgaeappearedon earth, oxygen concentration increased resulting in a shift fromreducingtypeofatmospheretoanoxidizingtype.Graduallyatmospherereacheditspresentcomposition,whichisideallysuitedforhumansandotherlifeformsthatareexistingtoday.

Thesurfaceorcrustoftheearthiscalledlithosphere.Itrepresentsthemountains,theoceanfloorsandtheplainlands.Theupperboundaryofthebiospherebeginsatthesoil,beneathourfeet,andmayextendtoadepthofeven150km.belowthesurface.

Do you know?

Surfaceoftheearthiscoolandsolid.Butaswemoveintothelayerbelow the lithosphere we reach the mantle having increasing heat andpressure.Atthecentreofthemantlecalledcore,temperatureoftheEarthisknowntobeveryhigh.Lithosphereallowslifetoflourishunlikethebarrensurfaceofotherplanets.

Concept Of Biosphere

Hydrosphere, atmosphere and lithosphere of theEarth togetherconstitutethebiosphere.Itisthesumtotaloftheallorganismsandtheirplacesofliving.Itextendsonlyafewkilometersbelowthesurfaceandextendsonlyafewkilometersintotheatmosphere.

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TheEarthistrulyadynamicplanet.OntheEarth,lifeisinfluencedbyitsphysicalenvironment.Atthesametime,thevariousfactorsintheenvironmentinfluencethelivingorganisms.Thistwowayprocessistheessenceofthedynamicnatureofourplanet.

Thescientificstudieswhichenableustounderstandthetotalityandpatternoftherelationsbetweenorganismsandtheirenvironmentiscalledecology.Itisalsoknownasenvironmental science.

Youwouldhaveobserved inyoursurroundings that there isanintricaterelationshipbetweenvariouscomponentsofnature.

Lookatthisexample.Greenplantsabsorbmineralnutrientsandwaterfromthesoil.Theleavesfruitsandotherpartsoftheseplantsareeatenbyanimalslikeinsects,birdsanddeer.Theseanimalsbecomethefoodforotherkindsofanimals.Whentheseplantsandanimalsdie,theirdeadremnantsdecayandsubsequentlytheyarebrokendownbymicroorganisms.Thebrokendownmattereventuallygoesbacktothesoil,thusconnectingallofthem.

Fig2.1Interactionsamonglivingorganisms

Averylargenumberofsuchconnectionsexistinnature.Theselinksarethefoundationsofthebalanceexistinginthenaturalworld.Theselinksexplainthetwobasiclawsofecology.

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• Wecannevercontinuetodoanyonethinginnature.

• Innatureeverythingisconnectedwitheverythingelse

Ifonehastounderstandandanalysealloftheseconnections,itisnecessarytocategorizethenaturalsystemintosmallerunits.

levels Of Organization

Letuslookatthenaturalsystemfromthepointofviewoflevels(hierarchy) of organization. It provides a convenient framework fordealingwithcomplexinterrelationships.Themostclearlyidentifiablelevelsareorganisms,species,populations,communitiesandecosystems.

Youknowthatanyformoflifecanbecalledanorganism.AlargenumberofvarietyoforganismsarefoundontheplanetEarthfromthesinglecelledAmoebatohumansandfrommicroscopicbacteriatohugebanyantrees.Anorganismrepresentsanindividualmemberofthenextlevelcalledspecies.

Youwill be able to recall that a species is a group of similarorganismssharingcommongeneticstructure.Hence,theyarecapableofbreedingonlyamongthemselves.Allhumanbeingsbelong to thespeciesHomo sapiens,dogsbelongtothespeciesCanis familiaris.Peaplantsbelongtothespecies Pisum sativum.

Acollectionofindividualsbelongingtothesamespeciesoccupyingagivenarea,atagiventimeiscalledpopulation.

Youwouldhavenoticed that a givenareawill havepopulationsofdifferentspeciesofplantsanimalsandotherorganisms.Allthesedifferentpopulationstogetherconstituteabiotic community.Membersofacommunityinteractwitheachother.

Thecommunityasawholewillbeinteractingamongthemselvesaswell aswith thenonliving components.Any suchunit innaturewherethereisaninteractionbetweenlivingandnonlivingcomponents,isknownasecosystem.Ecosystemformsthebasicunitofstudyinenvironmentalscience.

Earthhasdifferentkindsoflivingorganismslivinginavarietyofhabitats.Eachhabitathasasetofuniquefeatures.Hence,wehavevarities of ecosystems on this planet Earth. The different kinds ofecosystemsontheearthtogetherconstitutethebiosphere.

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Fig2.2Levelsoforganizationinnature

types Of ecosystem Wehavenowbecomefamiliarwiththeideathatecosystemforms

thebasicunitofstudyinenvironmentalscience.Itisalsothefunctionalunitinbiosphere.

An ecosystembydefinition consists of a community of differentkindsoflivingorganismsinanareainteractingamongthemselvesandwiththenonlivingcomponentsinthatarea.

Youhaveseenavarietyofecosystemsinyoursurroundingssuchasapondoragrassland,maybeyouhavevisitedaforestorasea.Haveyoueverwonderedwhatiscommontoallthese?Similarlyanocean,anestuaryandadesertalsorepresent typesofnaturalecosystems.Naturalecosystemscanbebroadlyclassifiedintoaquaticecosystemsandterrestrialecosystems.

Do this : Listtheexamplesofaquaticandterrestrialecosystems.

Therearealsomanyexamplesofman-madeecosystems.Themostfamiliarexampleistheaquarium.

Do this : Listafewmoreexamplesofman-madeecosystems.

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Activity 2.1

With the help of your teacher and classmates set up and maintain a small aquarium in your school.

Components Of ecosystem

Youwillbeabletorecallthatanyecosystemshouldhavetwobasiccomponents, thenon-living components and the living components,interactingwitheachother.

Thenon-livingcomponentsarealsocalledabiotic components.Theyrepresentthephysical,chemicalandclimaticconditionsoperatingintheenvironment.Physicalfactorsincludeairlight,heat,soilandwater.Chemicalfactorsarerepresentedbythevariousorganicandinorganicsubstanceswhetherrequiredornotbythelivingorganisms.Climaticfactorsarerepresentedbyrainfallandhumidity.

Thelivingcomponentsarealsocalledbiotic components. Theyarerepresentedbyplants,animals,bacteriaandfungi.

Youknowthatplantsaredescribedasautotrophssincetheyarecapableofmanufacturingtheirownfood.Apartfromgreenplants,algaealso belong to this category. The food prepared by these organismsis used by all other organisms either directly or indirectly.Hence,it is commonlysaid “all flesh is grass”.Hence,greenplants in landecosystemsandalgaeinaquaticecosystemaredescribedasproducers.

Animals areheterotrophs since they cannot prepare their ownfoodandreadilyconsumewhatisavailable.Hence,inanyecosystem,animalsaredescribedasconsumers.

Youknowthatanimalsdifferintheirfoodhabits.Thereareanimalswhich feed only on plants and they are called herbivores. In theecosystemsherbivoresaredescribedasprimary consumers,sincetheyobtaintheirfoodenergydirectlybyfeedingonplants.Thegrasshoppers,thedeerthecattleareallexamplesofprimaryconsumers.

There are animalswhichobtain their foodby eatingherbivores.Theyaredescribedassecondary consumers.Thegrasshoppersmaybeconsumedbyfrogs.Thedeerorcattlemaybecomethefoodforlionsortigers.Exampleslikefrogs,lionsandtigersaresecondaryconsumers.

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Someanimalsobtaintheirfoodbyfeedingonsecondaryconsumers.Theyrepresentthetertiary consumers.Thefrogswhichhaveeatenthegrasshoppersmaybecomethefoodforsnakes.Hence,inthisexamplesnakesrepresenttertiaryconsumers.

The producer and the different kinds of consumers primary,secondaryandtertiaryareinvolvedinanutritionalrelationshipinvolving‘eating and being eaten’.Theyrepresentdifferentlevelsoffeedingintheecosystemandhencearedescribedastrophic levels.Eachorganisminourecosystemisataspecificfeedingstagethatrepresentsitstrophiclevel.Letusgobacktothesameexampleswestudiedearlier

Fig2.3Atypicalfoodchain

example 1: Grass → Grass hopper → Frog → snakeexample 2: algae → Insect larve → Fishes → aquatic birds

TrophicLevel-1

TrophicLevel-2

TrophicLevel-3

TrophicLevel-4

Thiskindofnutritionalrelationship,wherethefoodenergyisgettingtransferredfromonetrophicleveltoanother,iscalledfood chain.

Inanyfoodchain,producersrepresentthefirsttrophiclevelandthedifferentlevelsofconsumerrepresentthesuccessivetrophic levels.Inanidealsituation,afoodchainwillhaveamaximumofthreeorfourtrophiclevels.

Therecanbehundredsandthousandsoffoodchainsoperatinginanecosystem.Itisbecauseanygivenplantcanbeafoodforavarietyofprimaryconsumers.Eachprimaryconsumerinturncanbeafoodformanyvaritiesofsecondaryconsumersandsoon.

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Foodchainscanbebroadlyclassifiedintothefollowingthreetypes.

• Grazing or herbivorous food chains where the primaryconsumersareplanteatinganimals.Mostof the foodchains inourecosystembelongtothiscategory.Suchfoodchainsarealsoknownaspredatory food chains.

Fig2.4AGrazingfoodchain

• detritivorous food chainswhere the primary consumer is adetritivore.Ants,termites,earthworms,millipedesandcrabsarecalleddetrivores because they feed ondetritus. It refersmainly to fallenleaves,partsofdeadtreesandsimilarkindsoforganicmatter.

example 3: detritus → earthworms → Birds• parasitic food chainswherethetransferoffoodenergyoccurs

throughaseriesofparasitesateachtrophiclevel.example 4: tree → parasitic birds → bird lice → flagellate protozoans

Here,birdsareparasiticontrees,liceareparasiticonbirdsandprotozoansareparasiticonbirdlice.

Sincemostorganismsfeedonmorethanonekindoffooditem,everyorganismateverytrophiclevelbecomeslinkedtoseveralfoodchainsatthesametime.Thus,ineveryecosystem,wehaveacomplexnetworkofinterconnectedfoodchains,forminga food web.

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Fig2.5Asimplefoodweb

Energy flow in the ecosystemhow does food become energy in organisms?

Variousorganismsfoundinanecosystemareconstantlygrowing,reproducing, dying and decaying. They need energy for all theiractivities.Whenorganismsconsumefood,thecarbohydratesintheirfoodbecomethesourceofenergy.Thisenergyisreleased,asyouareaware,throughaprocesscalledrespiration.Itmakesthestoredenergyinthecarbohydratesavailableforbiologicalwork.

Themainsourceofenergyforallecosystemsissolarenergy.Asyouknowonlygreenplantscantrapthisenergyandstoreitintheformofsugars,fatsandproteins.Whenprimaryconsumerseattheproducers,energyalsomovesupthetrophiclevel.However,duringthistransferalmost90%oftheenergyislosttotheenvironmentasheat,aforminwhichitcannotbeusedagain.Aswemoveupthetrophiclevels,theamountofusableenergyavailableateachlevelkeepsdecreasing.Onlyabout10%oftheenergyavailableinanygiventrophiclevelisgettingtransferredtothenextlevel.

Iftheproducerhas10,000unitsofenergytheprimaryconsumerreceivesonlyabout1000units,thesecondaryconsumergetsonlyabout100unitsandthetertiaryconsumergetsonlyabout10units.

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Fig2.6Energyflowinnature

Theenergyflowisthusunidirectionalandthelossateachstageissimplyreleasedintotheenvironmentasunusableheat.

It is for this reason that a food chainwill not havemore thanfourtrophiclevels.Veryrarelyafifthtrophiclevelcalledquaternary consumer canberecognised.

Fig2.7Afoodchainwithfivetropiclevels

Think : Amongtheexamplesyouhavestudiedhere,isthereafoodchainwhichhasquaternaryconsumer?

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What are ecological pyramids?Youhavenowunderstoodthenutritionalrelationshipbetweenthe

organismsatdifferenttrophiclevels.Theserelationshipsnotonlyinvolveenergybutalsothenumberofindividualsandtheirbiomassateachtrophiclevel.Itispossibletographicallyrepresenttheserelationships,whichassumetheshapeofpyramids.Suchgraphicalrepresentationsarecalledecological pyramids. Inanecologicalpyramidproducersoccupy the base and the different levels of consumers occupy thesuccessivetiers.Thus,mostoftenthetertiaryconsumersformtheapexofthepyramid.

A pyramid constructed based on the number of individualsoccupying a given trophic level, at a given period of time, is calledpyramid of numbers.Inmostoftheecosystems,formostofthefoodchains,thepyramidofnumberswillbeuprightsincethenumberofindividualsatthesuccessivetrophiclevelskeepsdecreasing.

Fig2.8Uprightpyramidofnumber

Lookattheparasiticfoodchain,herethepyramidofnumberisinverted!A pyramid constructed taking into view the biomass, which

isthedryweightofallthematterintheorganismsatatrophiclevel,is called pyramid of biomass. Formost of the food chains, the pyramid of biomass willbeupright. Insomeaquatic foodchains itmayinverted.

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Fig2.9Invertedpyramidofnumber

Apyramidconstructedonthebasisoftheamountofenergyfixedateachlevel,iscalledpyramid of energy.Inanyecosystem,foranyfoodchain,thepyramidofenergywillbealwaysupright.Youhavealreadylearntthattheamountofusableenergyavailableateachtrophiclevelisabout10%oftheenergythatwasavailableattheprevioustrophiclevel.Thisideaisverymuchinaccordancewiththelawsofthermodynamics.Know this : Thermodynamicsisthestudyofenergyrelationships,whichinvolves either utilization or release of energy. It is applicable to bothphysicalsystemsandbiologicalsystems.

Ifwewant tostudy the functioningofanecosystemwemustunderstand the basic principles of thermodynamics described aslawsofthermodynamics.

1.Thefirst lawstatesthatenergycanneitherbecreatednorbedestroyed,butcanbetransformedfromonetypetoanother.

2.Thesecond lawstatesthatnoenergytransformationsarehundredpercentefficient.Energyisalwaystransformedfromamoreusefulformtoalessusefulform.Totalenergycontentofasystemalwaysremainsaconstant.

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Biomagnification

Infoodchainsitisnotjustthenutrientsthatgettransferred.Severaltoxicsubstancesmaybetransferredfromonetrophicleveltoanother.Inmostofthesecases,theconcentrationoftoxicsubstancesincreases,astheypasstothehighertrophiclevels.

Such an increase in the concentration of a toxic substance ora pollutant, with every link in the food chain is calledbiological magnification or biomagnification.

Themost familiar example for biomagnification is the gradualincrease intheconcentrationofDDTinthetrophic levels inseveralfood chains. IndiscriminateuseofDDTasan insecticide, especiallyforeradicatingmosquitoes,hasnowresultedinDDTbeingdetectedinthetissueofsmallfishesandpredatorybirds.ddt has been detected even in mother’s milk!

Fig2.10BiomagnificationofDDTBiomagnificationdisruptsthebalanceinthefoodchains.Particularly

itaffectstheorganismsatthehighertrophiclevels.

extended learning activity :Visittoanearbyecosystem.

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exercises :

I. Four altertnatives are given to each of the following incomplete statement / question. Choose the right answer :1. Fillintheboxwiththenameofappropriateorganism

Grass→ →Frog→Snake→Eagle

a.deer b.lizard

c.grasshopper d.rat

2. Oneoftheseisadecomposer

a.fungi b.algae

c.protozoa d.insect

II. Fill in the blanks with suitable words :

1. ThecrustoftheEarthiscalled_______________.

2. Thebasicunitofstudyinenvironmentis______________.

3. Collectionofindividualsbelongingtothesamespecies,is_________.

4. Differentkindsofecosystemstogetherconstitute_______________.

5. Inaparasiticfoodchainthepyramidofnumberwillbe___________.

III. answer the following:

1. Listthefactorswhichhavemadelifetoexistontheearth.

2. Definethefollowing-

a.Lithosphere b.Population

c.Bioticcommunity c.foodweb

3. Whatisanecosystem?

4. WhyistheuseofDDTnotadvisable?

5. Constructasimplefoodchain.

6. Whatmayhappenifallherbivoresarekilledinaterrestrialecosystem?

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Chapter 3 StruCture of atom

after studying this chapter students :• statethepostulatesofDalton’satomictheory.

• describeJ.J.Thomson’sexperimentonthediscoveryofelectrons.

• listthecharacteristicsofcathodeandanoderays.

• describeRutherford’smodelofanatom.

• describeNeilsBohr’satomicmodel.

• listthethreefundamentalparticlesandtheirproperties.

• definethetermsatomicmassnumberandatomicnumberofanatom.

• definethetermisotopeofanelement.

• calculatethenumberofprotons,electronsandneutronsinagivenatom.

• feelproudwhentheyreadaboutthecontributionsofourscientists,toscience.

Youseeenormousvarietyofplants,animalsandmanyobjectsaroundus.Aretwoplantsortwohumansbeingsortwohillsidentical?Even two leaves from the same tree are not identical. Similarly,substancesmaybegases,liquidsandsolids.Somemaybecolourful.Letusknowthereasonsforthesedifferences.

Recall : In 600 B.C. the Indian sageKanāda was perhaps the firstto suggest thatall thematter ismadeupof very smallparticles called‘paramanu’.InSanskrit‘param’meansfinalorultimateand‘anu’meansparticle. He said that all living beings are composed of five elements:Jala’, ‘Agni’, ‘Pruthvi’, ‘Vaayu’ and ‘Akasha’.

ItwasKanādawhofirstpropoundedthatmaterialuniverseismadeup of ‘Kana’. An interesting story states that this theory flashed toKanādawhilehewaswalkingwithfoodinhishand.Ashenibbledatthefoodinhishand,throwingawaythesmallparticles,itoccurredtohimthathecouldnotdividethefoodintofurtherpartsandthus,theideaofamatterwhichcannotbedividedfurthercameintoexistence.Hecalledthatindivisiblematteras‘kana’.Indiantheoriesabouttheatomaregreatlyabstractandarebasedonlogicandnotonexperimentation.Thus,theIndiantheorieslackedanempiricalbase.

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InthefifthcenturyBCtheGreekphilosopherDemocrituscameupwithasimilaridea.Hethoughtofdividingapieceofasubstance,onewouldultimatelygetaparticlethatcouldnotbedividedfurther.Hegavethename‘atom’tothisultimateparticle.Allthesubstancesaremadeupofatoms.Asperthepresentconcepts,atomofDemocritusimplieseitheratomormolecules.

Aretheatomsofallthesubstancessimilar?Dotheyresembleoneanother?Letusdoanactivitytounderstandandexplainit.Activity 3.1

Take a small pieces of sodium and of iron and drop them into a 500 cm3

beaker containing water. What do you observe? Which reacts faster in water?

Activity 3.2

Take a small piece of sodium in a spatula . Ingnite it. Hold a piece of Magnesium strip in tongs. Ingnite it. What do you observe? Which burns very fast? Is colour of both the flames same? Sodium and Magnesium are made up of atoms. Are the nature of both the atoms same? Above activities show that atoms of different elements have different properties.

Takeprecautionswhileconductingtheaboveactivities.Anysubstancemadeupofsamekindofatomsiscalledelement.118

elementsareknowntous.Outofthis90arefoundinthenature,restaremadeinlaboratory.Activity 3.3

Make a list of elements that you use in day-to-day life. Write their uses and symbols.

atomic theoryIn1803EnglishchemistDaltonputforwardhisatomictheory.The

mainpostulatesofthetheoryareasfollows:1. Elementsaremadeupofverysmallindivisibleparticlescalled

atoms.2. Allatomsofaparticularelementareidenticalinshape,mass

andotherproperties,butaredifferentfromtheatomsofotherelements.

3. Atomsofoneelementcannotbeconvertedintotheseofanotherelement.

4. Atomsofanelementcombineinintegralratiowiththoseofotherelementstoformacompound.

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5. Anatomcanneitherbecreatednordestroyed.

Dalton’satomictheorywasthefirstmilestoneinexplainingtheinnerstructureofmatter. Itgaveapowerful initiative to thescientiststothestudyofmatterinthe19thcentury.

Howwouldanatombelike?Isitpossibletodividetheatomfurther?Afterconductinganumberofexperiments,scientistscame to knowwhat is inside an atom.Understanding thestructureofanatomenabledthemtoresolvemanymysteriesconcerningnatureandbehaviorofmatter.

Know this : The elements Astatin and Technetium are not added tothelistof90naturalelementsastheyoccuronlytoaminuteextentinNature.HoweverTechnetiumcanbemadeartificially.

fundamental particles : J.J. thomson’s experiment.Letuslookatthehistoryofdiscoveryofthesmallerparticleinside

theatom.J.J.Thomsonandothersconductedsomeexperimentsusingdischargetubeapparatus.Ittooktheworldofsciencetothesecretofcharges.

Fig3.1Productionofcathoderays

Adischargetubeisaglasstube,about15cmlongand3cm.indiameterconnectedtoavacuumpump.Metalelectrodesarefittedtotheendsoftheglasstube.

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J.J.Thomsoncreatedverylowpressureinsidethedischargetubeandappliedhighvoltage.Heobservedgreenishglowneartheanodeoftheglasstube.Therayswhichareemittedfromthecathodehittheanodeandcausethegreenishglow.Thestreamsofraysemittedfromthecathodearecalledcathoderays.Ifyouconnecttheplateofthedischargetubetoapositivesource,thenthatplateiscalledanode. (seefig:3.1).

J.J.Thomsonplacedalightpaddlewheelinthepathofthecathoderays.Thepaddlewheelstartedtorotate.Heconcludedthatcathoderaysareastreamofparticles.(seefig.3.2).

Fig3.2Experimenttodemonstratepropertiesofcathoderays

J.JThomsonappliedan electricfieldparallel to thepathof therays.Thecathoderaysdeflectedtowardstheanode.Heconcludedthatcathoderaysarenegativelycharged.(Seethefig3.3)

Fig3.3Experimenttodemonstratepropertiesofcathoderays

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ThoughJ.JThomsonconductedtheaboveexperimentwithdifferentgases, thesameresultswereobtained.Henamedtheseparticlesaselectrons. and these electrons arenegatively chargedparticles. It islighterthanHydrogenatom.Itsmassisverysmallwhencomparedtothatofanatom.Heshowedthatatomisdivisibleanditismadeupofverysmallparticles.Afterthediscoveryofelectron,thefirstpostulateofDaltonhadtobegivenup.

presence of positive charge in an atom:Ifanatomiscomposedofonlyelectrons,thenatomsandthemattershouldbenegativelycharged.Thefactisthatallmatterandatomsareelectricallyneutral.Doesitmeanthatatomscarrypositivelychargedparticlesalso?Toexplorethis,Goldsteinconductedanexperiment.

Fig3.4Productionofanoderays

In1886,Goldsteinusedamodifiedtypeofdischargetubewithaperforatedcathode.Heobservedthatcertainraysaretravellinginthedirection,oppositetothatofthecathoderays.Theseraysarecalledanoderays.(seefig:3.4)Heappliedanelectricfieldparalleltothepathofanoderays.Heobservedthatpathoftheraysdeflectedtowardscathode.

Whatconclusiondoyoudrawaboutthekindofchargeoftheanoderays?These rays containpositively chargedparticlesandare calledpositiverays.Thedeflectionofanoderaysinanelectricfieldwasverylittlewhencomparedtothedeflectionofcathoderays.Whyisitso?Thedeflectionofanoderaystowardscathodedependsonthetypeofgasestakeninsidethetube.

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Let us list out the different characteristics of anode rays.

1. Theyconsistofpositivelychargedparticles.

2. They are deflected by electrical and magnetic fields. Thedeflectionisverylittlewhencomparedtothedeflectionofcathoderaysbecausetheyconsistofheavyparticles(nucleus).

3. Thedeflectionoftheanoderaysdependsonthenatureofthegasinthedischargetube.Heavierthegaslowerthedeflection.

Whenhydrogengasistakeninsidethedischargetubethedeflectionwillbemaximum.Thepositiveparticlesofhydrogenatomsarefoundtobelightest.Theseparticlesarecalledprotons.Themassofoneprotonisaboutthemassof1840electrons.Thechargeofprotonisequalandoppositetothatofelectron.Weassumethatthemassoftheprotonas1 atomic mass unitanditsrelativechargeistakenas+1.

how are electrons and protons arranged in an atom? rutherford’s experiment

Itwasinitiallybelievedthatelectronsandprotonsareuniformlydistributed.Rutherfordconductedanexperimentwhichchangedtheentireconceptofdistributionofelectronsandprotonsinanatom.Letusstudy thisexperiment.Hedirectedhighspeedpositivelychargedparticlescalledalphaparticlestowardsathingoldfoil.Heobservedthatmostofthealphaparticlespassedthroughthefoilwithoutdeflection.A fewof themweredeflectedatvery largeangles fromtheiroriginaldirectionandafewwereeventurnedbackontheirpath.

Fig3.5

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this experiment raised several questions.

1. Whydidmostoftheparticlespassthroughthefoil?

2. Whydidafewofthemdeflectfromtheiroriginalpaththroughlargeangles?

3. Whydidafewofthealphaparticlesrebound?

Based on this experiment rutherford proposed a set of assumptions. they are

1. Positivelychargedparticlesofanatomareheldtogetherinthecentralregionoftheatom.Itiscallednucleus.Itissurroundedbyelectrons.

2. Thevolumeofnucleusissmallwhencomparedtothevolumeofanatom.

3. Themassofanatomisconcentratedinthenucleus.

4. Thenucleusispositivelychargedwhichisdifferentinmagnitudefordifferentelements.

5. Inaneutralatomthenumberofelectronsoutsidethenucleusareequaltothenumberofpositivelychargedparticlesinthenucleus.

Rutherfordnoticedthatatomicmassesofdifferentatomscouldnotbeexplained,ifonlyprotonsandelectronsarepresentinthem.Itwasobservedthattheactualmassofthenucleuswasmuchlargerthansumofthemassoftheprotonsthatmadeit.Hepredictedthatakindofneutralparticlewithmassequaltothatofprotonmustbepresentintheatom.

Themassofthenucleuswhichisofamuchhighermassisattributedtothepresenceofanothertypeofparticle.In1932JamesChadwickexperimentallyprovedthepresenceofsuchparticlesandcalledthemneutrons.Massofaneutronisalmostequaltothatofaproton.Theyarepresentinthenucleusoftheatom.

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Activity 3.4Complete the table

Atomic particle Discovered by Type of charge mass

Proton

neutrom

electron

SeveralscientistsdidnotagreewithRutherford’smodelofatom.Anelectronrevolvingaroundthenucleuscontinuouslyshouldloseenergy.Asaresult,itshouldbegraduallypulledtowardsthenucleusandendupcollidingwithit.Ifthisshouldhappenthentheatomwouldcollapse.Rutherford’satomicmodelcouldnotexplainthestabilityoftheatom.Anewtheorywaspresentedtoexplainthis.

In1913NeilsBohrpresentedamodelofanatom,whichisnowcalledtheBohr model.Thepostulatesofthismodelare,

1. Electronsrevolvearoundthenucleusonlyincertainpermissiblecircularorbits.Thisorbitiscalledshell.Thefirstshellfromthenucleusis‘K’ shellThesubsequentshellsareL,M,N,O,.,respectively.

2. Electronsineachshellhavebeenassociatedwithdefiniteamountofenergy.Electronsinhighershellhavemoreenergythanthosenearertothenucleus.

3. Theenergyofanelectronremainsconstantsolongasitrevolvesinitsownshell.the shells are also called energy levels. orstationaryenergylevels.

NeilsBohrproposedthateachshell(energylevel)canaccommodateamaximumof2n2electrons,wherenistheshellnumber.Forinstancen = 3 for the third shell. This shell accommodatesmaximum of2×32=18electronsonly.Thismeans‘M’shellcontainsnotmorethan18electrons.Canyoucalculatethetotalnumberofelectronsthatcanbepresentin‘N’shell?

YouknowthatneutralChlorineatomhas17electrons.AccordingtoNeilsBohr’smodel,outof17electronsthe‘K’shellaccommodates2electrons,‘L’shellaccommodates8electrons,andtheremaining7electronsareaccommodatedinthenextshellnamely‘M’shell.Thisisrepresentedinfigure.3.6

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Fig3.6electrondistributioninchlorineatom

Activity 3.5

Write the structure of Sulphur atom, showing the distribution of electrons.

ThemodeloftheatomthatemergedafterNeilsBohr’sproposalcanbesummedupasfollows.

1.Everymatterismadeupofatoms.

2.Anatomisnolongerconsideredtobeindivisible.

atomic number

Thenumberofprotonspresentinthenucleusofanatomisknownasatomicnumber.Italsorepresentsthenumberofelectronsintheorbits.ItisdenotedbyZ.Thetotalnumberofprotonsandneutronspresentinthenucleusofantheatomisknownasmassnumber.ItisdenotedbyA.GenerallyatomicnumberandmassnumberoftheatomofanelementarerepresentedbyasymbolZXa. ‘X’isanelement.

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Activity 3.6

Now you fill in the blank in the following table.

Nameoftheelement

Numberofprotons

Numberofelectrons

Numberofneutrons

Atomicnumber

Atomicmassnumber

Symbolicalrepresentation

HydrogenH

1 1 0 1 1 1H1

HeliumHe

2 2

NeonNe

10

UraniumU

92 238

OxygenO

8

SodiumNa

11

CarbonC

6 6

RadiumRa

88 226

AluminiumAl

13 27

Themodelofanatomhasundergonefurtherimprovementwhichyouwillstudyinhigherclasses.Youhavestudiedthatthenucleusofanatomcontainsprotonsandneutrons.Itisobservedthatiftheatomicnumberchangesthentheelementalsochanges.Forexample,ifanatomcontainsthreeprotons,ithastobeaLithiumatom.Ifanatomcontainssixprotons,ithastobeaCarbonatom.Doestheelementchangewhenthemassnumberchanges?LetusstudyaboutIsotopes.Isotopes:

Observe the followingfigures.Howmanyprotonsarepresent ineachatom?Ifoneprotonispresentintheatom,ithastobeaHydrogenatom.Observetheatomicmassnumberofeachatominfig3.7.Isitthesame?AtomsofanelementwithdifferentmassnumbersarecalledIsotopes.Hydrogenhasthreetypesofatoms.1H

1(protium/hydrogen)figure3.7(1),1H

2(deuterium)figure3.7(2),1H3(tritium)figure3.7(3).

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fig3.7(1)fig3.7(2)fig3.7(3)

Fig3.7Isotopesofhydrogen

AfterthediscoveryofisotopesthesecondpostulateofDaltonbecameinvalid,becausethesameelementhydrogenhasthreedifferenttypesofatoms.

exercises:

I. four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Theheaviestfundamentalparticleis

a.proton b.electron

c.neutron d.positron

2. Inthescatteringexperimentthedeflectionofalphaparticleisdueto

a.increaseinkineticenergy b.forceofrepulsion

c.forceofattraction d.decreaseinkineticenergy

3. Thesimplestatomthatdoesnotcontainneutronis

a.deuterium b.tritium

c.hydrogen d.helium

4. Thereasonfortheexistenceofisotopesischangein

a.atomicnumber b.electronnumber

c.neutronnumber d.protonnumber

II. fill in the blanks with the suitable words :1. Thetotalnumberofprotonsandneutronsinthenucleusofanatom

isknownas_________________.

2. Almostallthemassofanatomisconcentratedinasmallregionofspacecalledthe__________________.

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3. Theparticleofanatomthathasnochargeis_________.

4. Thefundamentalparticlenotpresentinanormalhydrogenatomis_________.

5. Theatomicmassofanatomis23anditsatomicnumberis11.theatomhas__________________neutrons.

III. answer the following:1. Mentionthepropertiesofcathoderays.

2. Whoproposedthatatomicnucleusispositivelycharged?

3. StatetheconclusionsdrawnbyscatteringexperimentofRutherford?

4. Whyisanatomneutralinspiteofthepresenceofchargedparticlesinit?

5. Namethefundamentalparticlespresentinanatom.

6. Define the terms atomic number and atomicmassnumber of anelement

7. Definetheterm‘isotope’ofanatomwithasuitableexample.

8. Fromthesymbol19K40state1.massnumberofPotassium2.atomic

numberofPotassium3.WritethedistributionofelectronsinanatomofPotassium.

IV. match the following :

A B

1. proton a.negligiblemass

2. ‘L’shell b.32electrons

3. electrons c. dalton’satomictheory

4. neutrons d.8electrons

e. electricallyneutral

f. positivelycharged

g. 18electrons.

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Chapter 4More about atoMs

after studying this chapter students :

• explainthetermsrelativeatomicmassandmole.

• calculatethenumberofmolesinagivenmassofasubstance

• estimate the amount of chemicals required for a chemical reaction usingmoleconcept.

• identifythevalenceelectronwhenatomicnumberofanelement

isgiven.

• definethevalencyofthegivenelement.

• recognise the relationship between valence electron and valency ofagivenelement

Themassofanatomisverysmall.Unitsofmasssuchasmilligram,gramandkilogramarenotconvenienttoexpresssuchsmallmasses. A suitable convenient unit has been developed by internationalcommitteeofchemists.Anisotopeofcarbonnamely6C

12atomhasbeenchosenasastandardforthispurpose.one-twelfthofmassoftheatom6C

12isotopeistakenasastandardtocomparethemassofotheratomsandmolecules.Thisunitiscalledatomic mass unitoronea m u

Know this : Howmuchisonea.m.u?Onea.m.u.=1.66× 10-24g.

=1.66× 10-27kg.

121 ofthemassofoneatomofcarbon6C

12isoneamu

i.e.1.66× 10-24g.

The relativeatomicmassof anelement is the ratioof themassof anatomof the element toone-twelfthof themassof anatomofcarbon6C

12.Inotherwords,itisanumberthatshowshowmanytimesan atom of an element is heavier than one-twelfth themass of an atomofcarbon6C

12.

Re lative actomic massmass of atom of isotope

mass of atom of the element

C121 1

1

612

#=

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Therelativeatomicmassesofsomeimportantelementsaregiveninthefollowingtable.

table 4.1 relative atomic Mass of some elements

Element Symbol RelativeAtomicMass

Element Symbol RelativeAtomicMass

Aluminium Al 26.98 Magnesium Mg 24.31

Calcium Ca 40.08 Nitrogen N 14.01

Carbon C 12.01 Oxygen O 15.99

Chlorine C1 35.45 Phosphorus P 30.97

Hydrogen H 1.008 Silver Ag 107.87

Howtocalculatetherelativemolecularmassofacompound?Letustakeanexample.

Carbondioxide:CO2

AtomicmassofCarbon=12,Atomicmassofoxygen=16

1×atomicmassofcarbon+2×atomicmassofoxygen.

1×12+(2×16)=12+32=44

Hence,relativemolecularmassofcarbondioxide=44

relative molecular massTherelativemolecularmassofasubstanceistheratioofthemass

ofamoleculeofthesubstanceto121 themassofanatomofcarbon

6C12

isotope.

1

Retan

lativemolecular massmass of atomof C

Mass of moleculeof thesubs ce

21 1

1

612

#=

Thus,therelativemolecularmassofasubstanceisthenumberthatshowshowmanytimesamoleculeofthesubstance,isheavierthanthatof

121 ofcarbon6C

12 isotope.

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Therelativemolecularmassofasubstance,elementorcompound-canbeeasilycalculatedbyaddingtherelativeatomicmassesofalltheindividualatomspresentinthemolecule.Activity 4.1

Find the relative molecular mass of water. Molecular formula of water is H20

Gram-atomic Mass

Gram atomicmass of an element is its relative atomicmassexpressedingrams.

Forexample,therelativeatomicmassofahydrogenatomis1.008,anditsgramatomicmassis1.008g.

Similarlygramatomicmassofoxygenis16g.

Gram molecular mass:

Grammolecularmassofasubstanceisitsrelativemolecularmassexpressedingrams.Thefollowingtablegivesgrammolecularmassofsomesubstances.

table 4.2 Gram Molecular Mass of some substances

Substance Molecularformula

Relativemolecularmass

Grammolecularmass

Hydrogen H2 2×1=2 2g

Oxygen O2 2×16=32 32g

Chlorine Cl2 2×35.5=71 71g

Water H2O (2×1)+16=18 18g

Hydrogenchloride

HCl 1+35.5=36.5 36.5g

Carbondioxide

CO2 12+(2×16)=44 44g

Sulphuricacid

H2SO4 (2×1)+32+(4×16)=98 98g

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Mole concept Youmight have read the stories of Tenali Ramakrishna and

Krishnadevaraya.YoumighthavereadthesimilarstoriesofAkbarandBirbal.Thestoriesarenotonlyhilariousbutfullofwisdom.

OnesuchstoryofAkbarandBirbalgoeslikethis.Akbarwanteda longstory tobenarrated. Birbalreadilyobligedhim,andstartednarratingthestory.Ajowarbaginafarmer’shomewasopenandthejowargrainswerespilled. Itwasunattendedto. Abirdnoticedthefoodgrainsandcameovertopickupagrain.Anotherbirdcameandpickedupagrain.Birbalrepeatedthesamesentencefourtofivetimes.At thisstage,Akbarsaid “stoprepeating,continue thestory. Whathappenednext?”Birbalsaid“howcanI?Allthegrainspresentinthebagshouldbepickedupbythebirdsfirst,andthenIcancontinuethestory”.AkbarrecognizingthewisdomofBirbalsmiledandsettledforsmallstories.

HowmanytimesshouldBirbalrepeatthesentence“Abirdcameandpickedupagrain”?Itdependsonthenumberofjowargrainspresentinthebag.

Howmanyjowargrainsarepresentinthebag?Apartfromphysicalcountingcanyousuggestamethodofknowingthenumberofjowargrainspresentinthebag?Countingthelargenumberofsmallparticlesisreallyadifficulttask.

Consideranotherexample.Duringlunchintervalastudentsaystohisfriend“giveme‘H2O’.Iforgottobringmywaterbottletoday.”Youhavestudiedthat,themolecularformulaofwateris‘H2O’anditisjustonemoleculeofwater.Thoughyouobligehimbygivingwater,doyougivehimjustonemoleculeofwater?Isthereanywaytoknowthenumberofwatermoleculespresentinthequantityofwatergiventohimbyyou?

Inthischapterweshalldiscussregardingmassandcalculationofnumberofsmallparticleslikeatomsandmolecules.

In day-to-day life , we use units like dozen, to deal withquantities. The terms dozen indicate constant number, whatevermay be the items. In a similarmanner to represent the numberof atoms ormoleculesweuse theword ‘mole’. A ‘mole’ is equal to6.023×1023atomsormolecules.Thisisalsocalledavagadro’s number andisrepresentedbyN.

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Avagadro

Know this : “Mole”representsthenumberofatomsor molecules in 22.4 litres of any gas at standard temperature and pressure (STP). (Standard temperatureandpressure)Thevolume22.4 litres isalsocalledgrammolecularvolume.

Importance of gram atomic massGramatomicmassofasubstancecontains6.023×1023atoms.

Forexample,gramatomicmassofoxygenis16g.Thatmeans16gofoxygencontains6.023×1023atoms.Ifweinhale16gofoxygenwewillbebreathing6.023×1023oxygenatoms.Similarly,grammolecularmassofanysubstancecontains6.023×1023molecules.Example:Grammolecularmassofwateris18g.Thatmeansifwedrink18gofwaterwewillbedrinking6.023×1023moleculesofwater.RememberH2Oindicatesonemoleofwater.

Do you know?

LordKelvin

Lord Kelvin inventor of the Kelvin Scale ofTemperature helped in calculating Avogadro’s number.Thisnumberisalsoreferedtoasmole.Moleisahugenumber,6.023×1023

Whichisequalto,

602,300,000,000,000,000,000,000

Moleconceptgivesusamethodofcalculatingthenumberofatomspresentinagivenmassofasubstance.Ithelpsinthecalculationoftheratioofreactantsconsumedandproductsformedquantitatively.Activity 4.2

Calculate the number of moles of water molecules in 1000 cm3 of water.

Know this : CountingbyweightisusedinReserveBanktocountthenumberofcoins.IntheAkbarandBirbalstory,wecanfindthenumberoffoodgrainsbyweighingthebagofjowarandcomparingitwiththeweightofonegrainofJowar.

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problem

Toprepareonegramofhydrogenmoleculesusinghydrochloricacid,howmanygramsofzincshouldbetaken?

Zn+2HCl→ZnCl2+H2↑

Gramatomicmasofzincis65gandthatofhydrogenmoleculeis 2g.Fromtheaboveequationwecanunderstandthat65gofzincgives2gofhydrogenmolecules.Toprepare1gofhydrogenmoleculesweneed32.5gofzinc.

Valency of an elementYouknowthatthemolecularformulaofsodiumchlorideisNaCl,and

thatofcalciumchlorideisCaCl2butnotCaCl.SimilarlythemolecularformulaofferricchlorideisFeCl3butnotFeCl.Thesedifferencesaredue to thecombiningcapacityofatoms.Valencycanbeconsideredas, thecombiningcapacityofanelement.Theknowledgeofatomicstructurehashelpedinbetterunderstandingoftheconceptofvalency.Themodernconceptofvalencyinitssimplestformcanbedefinedasthenumberofelectronsofanelementthattakepartinchemicalreactions.Forexample,valencyofchlorineis1,becauseitcanacceptorshareoneelectrontoformachemicalbond.Thevalencyofcalciumis2,becauseitcandonatetwoelectrons.Thevalencyofoxygenisalso2,becauseitcanacceptorshare2electronstoformabond.Thevalencyofcarbonis4,becauseitcanshare4electronswithotheratoms.Youwillstudymoreaboutchemicalbondsinhigherclasses.

Someelementsdonothaveanaturaltendencytoreactwithotherelements to form compounds. They are called inert gases ornoble gases.Forexample:Helium,Neon,Argon.(Theelementof18thgroupintheperiodictable)Theirvalencyiszero.Theseelementshaveeithercompleted shell of electrons or 8 electrons in the outermost shell (octet structure).

Heliumatomhas1shell(Kshell),thisshellcanaccommodateonly2electrons.Ithasacompletedshell.Itsvalencyiszero,oritischemicallystable.

SimilarlyelectronicconfigurationofArgonis,

K L M

2 8 8

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Ithasoctectstructure,itsvalencyisalsozero.Thusitisstable.Theelectronicconfigurationofchlorineatomis

K L M

2 8 7

It has an incomplete shell. It needs 1 electron, to complete theoctet structure. Its valency is1.Chlorineatomcanalsodonate the7electronsof theoutermostshellandgetoctetstructure.Then itsvalencybecomes7

Nowconsidersodiumatom,ithasoneelectronintheoutermostshell.Itdonates1electronandgetsoctectstructureinthe‘L’shellitself.Itsvalencyisalso1.

K L M

2 8 1

Activity 4.3

Atomic number of Aluminium is 13. find out its valency and valence electrons.

As a special case, some elements havevariable valency. Forexample,ironhastwovalencies-ferrous(2)andferric(3).Itisbecausethenumberofelectronsfromtheironatomswhichparticipateinthechemicalreactionwillbeeither2or3dependinguponconditions.

Activity 4.4

Complete the following table:

Nameoftheelement

Symboloftheelement

Atomicnumber

DistributionofelectronsKLMN

Valenceelectrons

Nitrogen N 7 2 5 5

Oxygen O 8 2 6

Sodium Na 11 2 8 1

Magnesium Mg 12 2 8 2

Silicon Si 14 2 8 4

Sulphur S 16 2 8 6

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exercises :

I. Four alternatives are given to each of the following incomplete statement/question. Choose the right answer.

1. Someelementshaveatomicmassinfractions.Itisduetothe presenceof

a.fractionsofprotons b.fractionsofneutrons

c.isotopes d.valenceelectrons

2. Plantsinagardenmakeuseof22.4litresofcarbondioxideatS.T.P.Thenumbersofmoleculesofcarbondioxideutilisedbytheplantis,

a.6.023×1023molecules b.22.4molecules

c.6.023×1024atoms d.11.2molesofmolecules

3. The atomic mass of Deuterium isotope of hydrogen is 2. The atomicmass of oxygen is 16. Then themolecularmass of heavy waterformedis

a.16 b.18 c.20 d24

4. Someelementscanhavedifferentvalencies.Itcanhappenduetothechangein

a.numberofelectronsthatparticipateinareaction

b.numberofneutrons c.numberofprotons

d.atomicmassnumber

II. Fill in the blanks with suitable words

1. Modernstandardformeasuringatomicmassis______________.

2. Averageatomicmassofchlorineis___________.

3. Molecularmassofwateris________________.

4. GrammolecularvolumeofagasatS.T.Pis________________litre.

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III. answer the following

1. Usingapieceofcalciumsulphateastudentwritestheword“mole”.Explainbrieflythemethodofcalculationoffindingthenumberofcalciumsulphatemoleculesusedtowritethewordmole. (Data: atomicmasses : Calcium= 40, Sulphur = 32, Oxygen=16)MolecularformulaofcalciumsulphateisCaSO4

2. CaCO3 Heat

CaO+CO2↑

Fromtheaboveequationcalculatetheamountofcarbondioxideingramsliberatedbyheating25gofcalciumcarbonate.

3. Astudentwrites“preparationofCO2”inthelaboratoryinhisbook.Fromthepointofviewofchemistrywhatisthemistakemadeinthiswriting?

IV. Match the following : A B

1. grammolecularvolume a. triatomicoxygen

2. ozone b. threeelectrons

3. valenceelectrons c. diatomicoxygen

4. modernstandard d. electronsoftheoutermostofshellatomicmass e. carbon6C

12isotope

f. 22.4liters

g. carbon6C14isotope

A nation’s culture resides in the hearts and in the soul of its people.

-Mohandas Gandhi

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CHAPTER 5STudy of CEllS

After studying this chapter students :• listthemajorpartsofacell.

• statetheroleofeachorganelleofacellfortheoverallactivityofthecell.

• comparethestructureandfunctionofchloroplastswithmitochondra.

• differentiateaplantcellfromananimalcell.

• recognizetheroleofdiffusionandosmosisinthefunctioningofacell.

• developtheskillofdrawingthediagramsofplantandanimalcells.

Study of CellsYouknow,thatallorganismsaremadeupofsmallunits,called

‘cells’.Asarethebrickstoabuilding,soarethecellstothebody.Youhavealreadylearntthatorganismsmaybeunicellularormulticellular.Activity: 5.1

Classify the following into unicellular and multicellular organisms.

Fig.5.1

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Thenumberofcellsinmulticellularorganismsmaybefromafewhundredstobillions.

Know this : Anaverageadulthumanbodyapproximatelyhastrillionsofcells.

1million=106(1000000)1billion=109(1000000000)1trillion=1012(1000000000000)100trillion=1014(100000000000000)

Cells perform activities such as nutrition respiration and celldivision,whichcontributetotheoverallgrowthofanorganism.Hence,cellsarecalledstructural and functional units ofanorganism.

Recall:Anorganismsuchashorsehasanumberoforgansystems.One such system is the circulatory system.Name an organ of thecirculatorysystem.Mentionatissueofthisorgan,andacellofthistissue.Youwillnotethatthecellisthebasicunitofanorganism.

cell tissueorgan organsystemorganism

bonecellbonetissueboneskeletalsystemwolf

Fig.5.2Cellisthebasicunitofanorganism

discovery of the cellManyscientistshavecontributedtothedevelopmentofcytology.

RobertHooke

Robert HookeRobertHookewasanEnglishscientist.Hedesignedamicroscopeandexaminedathinsectionofapieceofdriedcorkunderit.Hesawhoneycomblikestructuresin it. He called them ‘cells’. The word cellmeans‘smallroom’.

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M.J. Schleiden and Theodore Schwann

Schleiden,aGermanbotanistandSchwann,aGermanzoologist,togetherputforththe‘cell theory’ in1839.Celltheorystates

• Thebodyoflivingorganismsisformedofoneormorecells.

• All the cells arise only from preexisting cells throughcelldivision.

Nervecell Redbloodcell

Tracheids Fig5.3TypesofCells

Lookatfig.5.3 andobservethecellsofvariousshapes.Anervecellislongandhasbranchedfibrelikestructures.Anervecellcarriesmessages from one part of the body to another. A red blood cell isbiconcaveandroundinshape.Ittransportsoxygentodifferentpartsofthebodyofanorganism.Thus,cellshavedifferentshapestocarryoutdifferentfunctions.Givesomemoreexamplesofcellstoshowtherelationshipbetweentheirshapeandfunction.

Howsmallarethecells?Mostofthecellsarenotvisibletothenakedeye.Theyneedtobemagnifiedbyamicroscope.Howtoexpressthesizeofthecell?Ascellsareverysmall,ordinaryunitsarenotconvenienttoexpressthesizeofthecells.Micronisthemostcommonlyusedunittoexpressthesizeofthecell.Onemicronisequalto1/1000ofamillimetre.

Think : Isthedifferenceinthesizeofanorganism,duetothelargesizeofthecellsorlargenumberofcells?

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Thecellanditscomponentscanbeobservedclearlywiththehelpofanelectronmicroscope.Electronmicroscopeusesabeamofelectronstogettheimageoftheobject.Itsmagnificationisabout200000timesasagainstthecompoundmicroscope,whichmagnifiesobjectsupto2000times.

Fig5.4.CompoundMicroscopeFig5.5ElectronMicroscope

Know this :ACompoundmicroscopeisamuchimproveddesignoverthemicroscopedevelopedbyRobertHooke.

Howtofindthemagnificationproducedbythecompoundmicroscope?Lookatthecompoundmicroscopeinthefig.5.4.Observetheeyepieceinthecompoundmicroscope.Aneyepiecelensistheone,throughwhichwesee.Anobjectivelensistheone,whichisfacingtheobject.Findthemagnification,writtenontheeyepiecelensandtheobjectivelens.Forexample,inacompoundmicroscope,magnificationofeyepiecelensis10xandthatofobjectivelensis40x.Thetotalmagnificationis400x.Itmeans,theobjectappears400timeslargerthanitsactualsize.Activity 5.2

Find out the magnification power of a compound microscope, that you use in your school.

Howdoyouobserveacellundercompoundmicroscope?

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Activity 5.3

Peel off a thin layer from a piece of an onion. Put this in a watch glass containing water. Take a glass slide, put a drop of water. Transfer a small piece of the onion layer, on to the water drop on the slide. Put a drop of iodine or any suitable staining solution on this piece. Observe the slide, with the guidance of the teacher, under a compound microscope. Under the microscope, you will see the cells, usually as shown in the fig.5.6

Fig5.6Cellsinonionpeel

Observethecellsinfig.5.7,andfig.5.8.Anycell,whenobservedunderacompound.microscope,shows threeprominentparts.Theyarecell membrane,cytoplasmandnucleus.Acellissurroundedbyacell membrane.Itisalsocalledplasmamembrane.Itseparatestheinteriorofthecellfromoutsideenvironment.Cellmembraneformstheboundaryofthecell.Ithelpstomaintaintheshapeofthecell.Itcontrolsthemovementofselectedsubstancesintooroutofit.Hence,cellmembraneisdescribedasasemipermeablemembrane.

Themovementofmoleculesacrossthecellmembraneoccursbytwoprocesses.

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Fig5.7AnimalCell

Fig5.8PlantCell

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Howdotheseprocessesoccur?Letusconductanexperiment.

Activity 5.4

Experiment to demonstrate diffusion

Take some water in a beaker. Drop a crystal of potassiumpermanganateintoit.Observethechangeinthecolourofwater;whetherthechangewasgradualorimmediate.Thechangeisduetothemovementofmolecules. Potassium permanganate has diffused. This process ofmovementofmoleculesiscalled‘diffusion’.Diffusionisaprocessinwhich,moleculesmovefromaregionofhigherconcentrationtoaregionoflowerconcentration.

Fig5.9Experimenttodemonstratediffusion

Think : Howdoesoxygenmovesinandoutofthecell?

Letustakeanothersituation,inwhichthemoleculesmovefromaregionofhigherconcentrationtoaregionoflowerconcentration.We shal l conduct anotherexperiment.

Activity 5.5

Experiment to demonstrate osmosis

Makeacupshapedcavityinapeeledpotatoasshowninfig5.10.Poursugarsolution intothecavity.Placethepotato inacontainerhalfimmersed inwater.Mark the levelof sugarsolution.Leave it forabouthalfanhour.Notetheriseinthelevelofsugarsolution.Whydiditrise?It is due to the movement of water molecules from a region of higherconcentrationtoaregionoflowerconcentration.However,themovementofmoleculesisthroughthesemipermeablemembraneofthepotato.Thisprocess is called ‘osmosis’.Osmosis is a special kindof diffusion. It isthe diffusion of water molecules through a semipermeable membrane.Hence, osmosis is the movement of water molecules from a region ofitshigherconcentrationtoaregionofa lowerconcentration, throughasemipermeablemembrane.

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Fig.5.10Experimenttodemonstrateosmosis

Movement ofmolecules across theplasmamembrane of cells isusually froma regionofhigher concentration to the regionof lowerconcentration. Under certain conditions,moleculesmove from aregionoflowerconcentrationtoaregionofhigherconcentrationwiththe expenditure of energy.For example, inblood, the concentrationofsodiumislessanditismoreinaheartmusclecell.Inspiteofthis,sodium isabsorbed into theheartmusclecell, fromtheblood.Thisprocessrequiresenergy.Thisiscalledactive transport.

Lookatthefig.5.8.Inplantcells,inadditiontothecellmembrane,there is a cellwall. Cellwall is thick, rigid and surrounds the cellmembrane.Itismainlycomposedofcellulose,anonlivingsubstance.Cellwallprovidesshape,strength,protectionandrigiditytothecell.

Cytoplasm isajellylikesubstancefoundwithinthecellmembrane.Nearly80%ofcytoplasmiswater.Itistheseatformostofthecellularactivities.Anumberofsmallercomponentsarefoundinthecytoplasm.They include nonliving substances and living substances called‘organelles’.Nonlivingsubstancesincludeseveralchemicalssuchasstarchgrains,oildroplets,calciumcarbonate,resinandgum.Someofthemareusedasreservefood,somearewasteproductsandtheothersaresecretions.

The living componentsare calledorganelles.Organellesare thespecializedstructuresfoundinthecell.Theycarryoutspecificfunctions.Theyaregroupedundertwocategories.Theyare-

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1. Organellescoveredbymembranescalledmembranous organelles.

Examples:Endoplasmicreticulum,mitochondria,golgicomplex,lysosome,plastids.Lookattheorganellesmarkedinthefig.5.7and5.8.

2. Organelles which are not covered by membranes callednon membranous organelles.Examples:Ribosomes,centrioles.

Membranous organelles

Endoplasmic reticulum :

Fig.5.11Endoplasmicreticulum

Endoplasmicreticulumisanetworkofmembranes.Itextendsfromthecell membrane to the nuclearmembrane.Endoplasmicreticulumformsthesupportingframeworkofthecell. It transportssubstancesfromonepartofthecelltotheotherandfromonecelltoanother.

Mitochondrion: Observethefig5.12.Mitochondriaoccurinvariousshapes, such as, cylindrical, spherical, oval and rod shaped. Eachmitochondrionisboundbyadoublemembrane.Outermembraneissmoothbutinneroneisfolded.Foldsarecalledcristae.Innermembraneencloses a mass known as matrix. Mitochondria are the

Fig5.12Mitochondrion

sites of respiration in a cell.They use oxygen to breakdown glucose into carbondioxideandwater.Thisprocessreleases energy, which isstored in amolecule calledadenosine triphosphate.Thisin short is known asATP.Hence,mitochondriaarecalled‘power houses of the cell’.Normally,acellhas30to40

mitochondria; but the number ofmitochondria in a cell varies anddependsonthefunctionofthecell.

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Think: Flightmusclecellsininsectscontainthousandsofmitochondria.Why?

Golgi complex :Golgicomplexconsists

Fig5.13GolgiComplex

ofdifferenttypesofstructures.Somearetubelike,afewareintheformof granules. Themain function ofgolgicomplexistosecretechemicalsrequiredforcellularactivities.

lysosomes : Lysosomesareusuallyfound in an animal cell. They arespherical,saclikeorganelles.Theycontain a variety of hydrolyticenzymes.Theseenzymeshelpinthedigestionoforganicsubstances,presentinthecell.Theymayalsodestroytheirowncell,whenitbecomesold,weak,damagedordiseased.Hencetheyarecalled‘suicide bags of the cell’.

Know this : Lysosomesuseabout40differenttypesofenzymes,whicharemanufacturedintheendoplasmicreticulumandmodifiedinthegolgicomplex.

Plastids

Plastidsare foundonly inplantcells.Someplastidsarewithoutcolouringpigmentsandarecalledleucoplasts.Theyoccurinregionsofplant,whicharenotexposedtosunlight,suchastenderrootsandstems.Theyaremainlyinvolvedinthestorageofreservefood.Someotherplastidsarewiththecolouringpigments.Theyarecalledchromoplasts.Chromoplastscontainpigmentsthataregreen,yellow,red,orangeincolour.Thegreencolouredchromoplastsareknownaschloroplasts.Inchloroplasts,greencolouredpigment,namelychlorophyllisinlargeramount thanother colouredpigments. Theyare found in the greenpartsoftheplantssuchasleaves.Lookatfig.5.14,tounderstandthestructureofchloroplast.

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Fig5.14Chloroplastinsection

Chloroplast:

Eachchloroplastiscoveredbyadoublemembrane.Theinnermembrane encloses amatrix.Matrix consists of stroma andgrana.Granahas chlorophyll.Chlorophyllplaysanimportantrole in preparing food.Whatexactlyistheroleofchlorophyll?Youwilllearnmoreaboutthis,inthenineteenthchapter.

Think : A tender tomato is whitish in colour. Later it becomes green.Furtheritturnsred.Why?

Non membranous cellorganelles

Ribosomes : Youwillfindsomegrainlikestructuresattachedtotheendoplasmicreticulum.Theseareribosomes.Ribosomesarealsofoundattachedtothenuclearmembrane.Theyarefoundeveninthenucleolus.Theyplayanimportantroleinthesynthesisofprotein.Hence,theyareknownas‘protein factories of the cell’.

Centriole : Lookatfig.5.7,toidentifytheorganellecalledcentriole.Centrioles are found in some algae, fungi and all animal cells. Twocentriolesarelocatedusuallynearthenucleus.Centrioleshelpduringcelldivision.

In the cell, wewill also findmembrane covered cavities calledvacuoles.They are filled with a fluid called cell sap. Vacuoles arestructureswhichstorefood,excesswaterandwasteproducts.

Know this : Mostoftheprotozoanshavevacuoles.Vacuoles,whichstorefoodandhelpindigestion,arefoodvacuoles. Vacuoles,whichhelpintheremovalofexcesswater,arecontractilevacuoles.

Nucleus

Nucleusisasphericalorganellefoundinalleukaryotes.Recallwhateukaryoteis.Nucleusisthelargestorganelleinacell.

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Fig5.15Nucleus

Most of the eukaryotic cellsusuallyhaveonenucleus.Somelikeslimemoldshavemanynuclei.Somemammaliancellslikeredbloodcellsdonothavenucleusatmaturity.

Think : Mammalianredbloodcellsdonotcontainnucleusatmaturity.Why?

Nucleus is covered by adoublemembrane called nuclear membrane.Themembraneencloses

a fluid callednucleoplasm Nucleoplasm has a network of threadlike structures called chromatin. During cell division chromatinundergoescoilingandsupercoilingandbecomesshortandthicktoformchromosomes.

ChromosomescontaingeneticmaterialcalledDeoxyribosenucleicacid.Inshort,itiscalledDNA.DNAhasgenes.Eachgenedeterminesaparticularcharacteristicofanorganism.Forexample,heightofaperson,colouroftheskin,colouroftheeyeslikeblack,blue,greenorbrown.

Normally,everycellofanorganismofaspecieshasadefinitenumberofchromosomes.Everyhumancellhas46chromosomes.Lookatthegiventabletoknowthechromosomenumberofsomeorganisms.

Table 5.1 Chromosome number in some organisms

organism Chromosome Number

RoundwormOnionCatMangoMonkeyDog

21638405478

Lookatthestructureotherthanchromatininthenucleus.Nucleusalso has a dense spherical body callednucleolus. Nucleolus is notcoveredbyamembrane.Nucleolusenclosesribosomesandthusinvolvesinthesynthesisofprotein.

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Nucleusco-ordinatestheactivitiesofthecell.Forinstance,lookatthegivenillustrationsaandbcarefullyinfig5.16.

Fig5.16Illustrationsaandb

Fromtheaboveillustrations,canyouestablishtheimportanceofnucleus?Activity 5.6

List the major differences between a plant and animal cell by looking at the diagrams: 5.7 and 5.8.

PLANT CELL ANIMAL CELL

1 Cell wall

2 Plastids

3 Vacuole

4 Centrioles

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Exercises :

I. four alternatives are given to each of the following incomplete statement / question. Choose the right answer :

1. Acelllackinginnucleus,alsolacks

a.plasmamembrane b.mitochondria

c.chromosome d.vacuole

2. Cellwallisabsentinthecellofthisorganism

a.mushroom b.moss

c.fern d.mosquito

3. Organelleofthecell,whichreleasesenergythroughrespirationis

a.Golgicomplex b.Mitochondria

c.Lysosome d.Chloroplast

4. Whichofthefollowingpartofacellisnon-living?

a.cellwall b.mitochondria

c.cellmembrane d.lysosome

5. Oneofthefollowingisthesmallestorganelleinacell

a.lysosome b.nucleolus

c.ribosome d.chromosome

II. fill in the blanks with suitable words:

1. Theinstrumentthatledtotheunderstandingofcellis___________.

2. Theorganelle,whichcontrolsthevariousactivitiesofthecell,is_____.

3. Theorganelle,whichiscalledthe‘kitchenoftheplantcell’is_____.

4. Thesitesofproteinsynthesisinthecellare_____________.

5. Themainchemicalcomponentofthecellwallis_____________.

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III. Match the following:

A B1. storageroomofthecell a. chloroplast

2. gatewayofthecell d. golgiComplex

3. solarpanelsofthecell c. vacuole

4. packagesofhereditaryinformation d. cellwall

e. chromoplast

f. cellmembrane

g. chromosome

IV. Answer the following questions:1. Whataregenes?Mentiontheirimportance.

2. Which organelle is responsible for the formation of spindle fibresduringcelldivision?

3. Whichisthemostimportanttypeofchromoplast?Why?

4. Which are the organelles that are found more in number in thefollowingcells?

a.musclecells b.whitebloodcells

c.leafcells d.pancreaticcells

5. Listanyfourdifferencesbetweenaplantcellandananimalcell.

6. Diagramsoftwodifferentcellsaregivenbelow.Whichoneofthetwoisaplantcell?Supportyouranswer.

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1. Nametheparts1,2,3and4.

2. Writethefunctionsof1and3.

3. Drawalabelleddiagramof4asseenunderanelectronmicroscope.

7. Drawalabelleddiagramofaplantcell

V. Suggested Activities

1. Putdriedraisins(drygrapes)inadishwithwater.Whatisthechangeinthesizeofraisinsaftersometime?Why?

2. Remove the shell of an egg by dissolving it in dilute hydrochloricacid.AthinouterskinnowenclosestheeggPuttheegginwater.Observeafterafewminutes.Whatisyourinference?

3. Place a similar de-shelled egg in a concentrated salt solution fora few minutes. Observe the changes. Record your observationsgivingreasons.

Habits : Cultivate regular habits of prayer, meditation and reading inspiring and strengthening literature.

-Swami Vivekananda

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CHAPTER 6

ClAssifiCATion of living oRgAnismsAfter studying this chapter students :

• explaintheimportanceofbiologyindailylife.

• describetheneedfortheclassificationoflivingorganisms.

• identify the efforts of scientists, in developing systematicclassification.

• recognizetheevolutionarybasisofclassification.

• note the diversity in the living organisms and the fundamentalsimilartiesinthelifeforms.

• identifytheorganismsthattheyseearound.

• classifythelivingorganismstotheirrespectivekingdoms.

• developtheskillindrawingthediagramsoforganisms.

nature, scope and Branches of Biology

Natureisbeautifulwithawidevarietyofplantsandanimals.Plantsandanimalsdiffer instructure, function,shape,colour, lifeprocessandothercharacteristics.Isitnotniceandinterestingtoknowaboutplants,animalsandotherlivingorganisms?

scope of Biology

Biologyisknownasanaturalscience.Biologyisthestudyoflifeandlivingorganisms.

Thestudyofbiologyhelpsusto,

• answer countless questions related to life, such as, are there plantswhicheat insects? Is a virus livingornon living?Why docellsdivide?Howdocellsage?

• increasethepowerofobservation.

Observethevarietyofleavesofdifferentplants.

• understandtheapplicationofbiologytohumanlifeandsociety.

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Activity: 6.1Civic body carries domestic wastes in vehicles. What do they do with the

waste materials? – collect information.

• knowmoreaboutourselves.Activity: 6.2

During P.T. period, you run in the play ground for about two minutes. What will be the change in the rate of your breathing and heart beat? Why?

• producemorefoodfromplants.• controlanumberofdiseases.

Think : Isitnottheresponsibilityofeveryonetokeepthesurroundingsclean?• createanawarenessaboutconservationofnaturalresourcessuchas

minerals,water,plantandanimallife.• Donotkeepopenthetap,tillyoufinishbrushingtheteeth.• developinterestinghobbiessuchas,vegetablegrowing,petkeeping,

fishrearing.• developaconcernforlife.• understandtheinterdependenceofplantsandanimals.

Activity: 6.3 Make a list of the plant products used by you in a day, from morning till night

Think : Doplantsneedanimalsfortheirexistence?

Branches of Biology Biologyisdividedintoseveralbranchesfortheconvenienceofstudy.• Botanydealswiththestudyofplants.• Zoologydealswiththestudyofanimals.• Microbiologyisthestudyofmicroorganisms.• Cytologyisthestudyofcells.• Histologyisthestudyoftissues.• Physiology deals with the processes and the functions of

livingorganisms.• Biotechnologydealswiththeapplicationoftechnologyinthe

fieldofbiology,forthebenefitofmankind.

Find out : Theothermajorbranchesofbiology.

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Classification of Livng OrganismsEarthisinhabitedbyinnumerableorganisms.Scientistshavefound

anddescribedapproximately1.9millionspeciesonearth.Inadditiontothis,newspeciesarebeingdiscoveredeveryday.Therearemicroscopicorganisms like bacteria and yeast; small plants like coriander andtulasi;largeorganismssuchaselephant,whaleandbanyantree.Someorganismsliveinwater;someonland;afewindesertsandafewothersinthepolarregions.Doyouknoworganismslivinginotherenvironments?

Diversity among the organisms is amazing and beyond ourimagination!Findthereasonsforthedifferencesinshape,size,colourandmodeofnutrition,amonganimals.Weknowthattherearemanyorganisms on the earth. It is very difficult to study each and everyoneofthemtounderstandtheircharacteristicfeatures.Forthesakeof convenience of study, organisms are grouped according to theirsimilarities and differences. A detailed study of a typical organismofthegroup,helpsustounderstandthemaincharacteristicsofthewholegroup.Thus,groupingmakesourstudyeasier.Themethodofgroupingorganisms,accordingtotheirsimilaritiesanddifferencesiscalled‘classification’.Taxonomyisthebranchofbiology,whichdealswiththeclassificationoforganisms.The purpose of classification is

• forconvenience-easytostudy,identifyandremember.• toshowrelationshipsamongvariousgroupsoforganisms.• toshowtheevolutionoforganismsfromsimpletocomplexformsof

life.

Think: How does the knowledge of classification help in your dailyactivities?Howwouldyouusetheideaofclassificationtodothefollowing?

A.arrangingyourbookshelf.B.preparingastudytimetable.

Activity: 6.4

Group the following animals into herbivores and carnivores.

Tiger, cow, elephant, wolf, deer, crocodile, squirrel and parakeet.

Activity: 6.5

Group the following plants under the headings food, furniture and medicine: Tulasi, ragi, honne, garlic, teak and potato.

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Contributions of ancient scientists for the classification of living organisms

Charaka

Charaka : (600 BC) Charaka, an ancient Indian sage, was a

philosopher, astronomer and physician. He hadlistedabout340planttypesandabout200animaltypes in his book ‘Charaka Samhita’. CharakaSamhita is considered as the most ancient andauthoritativewritingonayurveda.Charakaforhiscontributionsisknownas‘Father of ayurveda’.

Know this : CharakaSamhita,mentionsthegradualdevelopmentoffoetuswithin the womb inminute detail. It accurately resembles themodernmedicalversion.

Aristotle : (384-322 BC) Aristotlewas a greatGreek philosopher and a

Aristotle

biologist.Hiswritingscovermanysubjects,suchas, physics, biology, logic,music, and politics.Aristotlefollowedspecificmethodsofinvestigationlikeobservation,description,surveys,comparisonandclassificationinstudyingthelivingorganisms.He dissected many animals to study theirstructure.

Aristotleclassifiedplantsandanimalsintothreegroupseach

Plants: •Herbswithsoftstems. •Shrubswithseveralwoodystems. •Treeswithasinglewoodystem.Animals: •Aquaticanimals,foundinwater. •Terrestrialanimals,foundonland. •Aerialanimals,foundinair.

Aristotle, because of his contributions, is popularly known as‘Father of Biology’.

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Parashara

Parashara: (100 BC.) Parashara, an ancient Indian sage, inhis book ‘Vrikshaayurveda’ had given aclear description of plants and divided theplants intoseveral ‘ganas’. Itwasbasedonthe characteristics of flowers. This type ofclassification, ismuch similar tomodernclassification.Parashara’sanotherbook,‘Krishiparashara’, iswrittenforthebenefitoffarmers.Thebookcanhelpthefarmerstoplanandmanagethe

activityoffarming.AccordingtoParashara,windfromthenorthorthewestbringsrainfallandthatfromtheeastorthesouth,indicatesnorain.

Corolus Linnaeus: (1707-1778 A.D.) LinnaeuswasaSweedishbiologist.Hehad

CorolusLinnaeus

recordedabout6000speciesofplantsinhisbook,‘Species plantarum’ published in1753.Hehadgiven a detailed system of his classification inanotherbook,called‘Systema naturae’,inwhich,hehadclassifiedabout4,400speciesofanimalsand7,700speciesofplants.

Linnaeus had proposed two kingdoms,kingdom Plantae andkingdom Animaliainhisclassification.Heintroducedfourcategoriesfor grouping organisms -class, order, genus and species in eachkingdom.Modern classification adds twomore categories. Theyare-phylum and family. Hence,modern system is an extensionof Linnaeus system of classification. Linnaeus also introducedthe scientificmethod of naming the organisms called, ‘binominal nomenclature’. For these contributions Linnaeus is considered as‘Father of modern taxonomy’.

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Do you know?

CorolusLinnaeuswasthefirstpersontoplacehumansinasystemof biological classification. He placed humans andmonkeys under thesamegroup–‘primates’.Thisclassificationreceivedcriticismfromotherbotanists.Linnaeussilencedthembysaying,“Manlearnstoknowhimself.Let’sgiveupquibbleoverwords.Oneshouldnotgiveventtohiswrathonanimals”.

Kingdom↑

Phylum↑

Class↑

Order↑

Family↑

Genus↑

Species

ModifiedLinnaeanHierarchy

The seven levels of Organization:Youhave already learnt about the

levels of organization in your lowerclass.Youalsoknowthatthebasicunitof classification is species. The nextlevel is genus and then family. Latercomes the order, class, phylum andkingdom. Kingdom forms the highestlevelofclassification.ThisisthemodifiedLinnaeanhierarchy.

Recall : Whatisaspecies?

Binomial nomenclature

Binominalnomenclatureisthescientificmethodofnamingthelivingorganisms.Commonnamesoftendifferfromonepartofacountrytoanotherandcertainlyvaryfromonecountrytoanother.Incontrast,scientific name can be used all over theworld speaking differentlanguages.Itavoidsconfusion.

Activity: 6.6

What is Cat called in Kannada, Tamil, Telugu, Malayalam and Hindi?

Every scientific name has twowords. The first word refers tonameofthegenusandthesecondtonameofthespecies.Scientificnames arewritten in Latin andGreek. In print, they are always inItalics. If handwritten, they are underlined.Ficus religiosa is thebinomialnomenclatureofpeepultree.Equus caballus; isthebinomialnomenclatureofhorse.Thefirst letterof thefirstname, thegenus,

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always beginswith a capital letter and that of the second- species,is a small letter.Scientificnameshaveabackground.For example,scientificnameofmangois‘Mangifera indica’. Mangiferameanssweetfruit;indicaindicatesitsorigininIndia.Man-‘Homo sapiens’. Homomeanshuman;sapiensmeanswise.Dog- ‘Canisfamiliaris’. Canis-havingcanines;familiaris–mostfamiliar.

Activity 6.7

Take up an activity under eco club and try to collect such information about plants and animals found in your school campus.

Think : Donkeybelongstothespecies ‘asinus’.Bothdonkeyandhorseare included in the samegenus.What is thebinomialnomenclatureofdonkey?

Some animals have the same species and genus name. For example cobra- Naja naja.

Do you know an animal, having the same common name, genus name and species name?

Letusunderstandclearlythesevenlevelsofclassificationwithafewexamples.

Systematic position: Itisthedescriptionofanorganismintermsofthevariouslevels,towhichitbelongs.

Systematic position of human

Activity: 6.8

Focus on the given example, ‘human’. You know that there are seven levels of classification. Remember each subsequent level eliminates animals that could be included in the previous level. All of you know, that human is an animal. So, human is included under animal kingdom. Consider some examples for animals. Human has a notochord. So human is placed under the phylum Chordata. Hence, eliminate all the non chordates, if you have given such examples. Now give examples only for vertebrates. Humans belong to the class mammalia, as they have mammary glands, which secrete a nourishing fluid, called milk. Hence, remove all the other vertebrate examples, which are not mammals. Like this, proceed with order, family, genus and species.

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Table 6.1 Systematic position of human

Level Human Characteristic feature

Kingdom Animalia Heterotroph,bodilymovement

Phylum Chordata Notochord

Class Mammalia Mammaryglands

Order Primate Erectposturewithbinocularvision.

Family Hominidae Forelimbsareshorterthanhindlimb

Genus Homo Human-largecranium;toolmakingability

Species sapiens Highlydevelopedbrain,capableofthinkingandspeaking.

Systematic position of mangoDothesameexercisetopresentthesystematicpositionofmango.

Level mango

Kingdom Plantae

Phylum Magnoliophyta

Class Magnoliopsida

Order Sapindales

Family Anacardiaceae

Genus Mangifera

Species indica

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Systems of classificationClassification of living organisms is probably as old as human

civilization.Theearliestclassificationwasprobablyonthebasisofutility,inmeetingtheimmediateneeds.Plantswereclassifiedasedibleandnonedible;animalswereclassifiedasusefulandharmful.Discoveriesofneworganismshave ledtotheperiodicalrevisionofclassificationfrom‘twokingdomsystemtofivekingdomsystem’.Itislikelythatthenumberofkingdomsinfuturemayincrease,becauseofmoreandmorediscoveries.

Ancient system of classificationAncientsystemclassifiesorganismsonthebasisofoneormore

superficial similarities and differences among the organisms. Forexample,plantsweregroupedonthenatureofthestem,intoherbs,shrubsandtrees.Animalsweregroupedonthebasisofhabitat,intoaquaticanimals, terrestrialanimalsandaerialanimals.Thistypeofclassificationledtotheinclusionofunrelatedorganismsinonegroup.Let usunderstand clearly,with the help of an example. Terrestrialanimals includedearthwormandtiger,alongwithotheranimals. Inspiteofmanyotherdifferences,earthwormdiffersfromthetigerinnothavingabackbone.Canyouthinkofsuchotherexamples?

ThesystemofclassificationputforthbyParasharaandAristotlewerebasedmainlyonsuperficialcharacters.Inventionofmicroscopehelpedustounderstandeventheminutesimilaritiesanddifferencesbetweentheorganisms.This,ledtoasystematicandscientificapproachtoclassificationandtothedevelopmentofmodernclassification.Modernclassificationisalsocalledthenatural system of classification.Modernclassificationhassomemerits.Itincludestherelatedorganismsinonegroupandshowsrelationshipswithregardtohabitat,lifeprocessandmodeofreproduction.

Two kingdom classification:Oneoftheearliesttypeofclassificationinthemodernsystemisthetwokingdomclassification,introducedbyCorolus Linnaeus in 1758. It lasted for about 100 years. Linnaeusclassifiedthelivingorganismsundertwokingdoms.Theyarekingdom plantae andkingdom animalia. He included all the plants underplantaeandanimalsunderanimalia.Asthediversityamongthelivingorganismsbecamemoreandmoreevident,Linnaeanclassificationhadtoberevised.

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Know this : Linnaeusincludedmushroominkingdomplantae.Mushroomsdonotpreparefoodlikeotherplants.

Activity: 6.9

Observe the fig. 6.1

List the plant like and animal like parts of Euglena.

Doyouincludeeuglenaunderplantkingdomoranimalkingdom?Discuss.

Three kingdom classification

In1674,Leeuwenhoek,observedprimitive

Fig6.1Euglena

organismsunder amicroscope. Till that time,their existencewasunknown. To give a rightplacetosuchorganisms,Ernst Haeckel in1866,proposed a third kingdom, ‘Protista’, andincludedalltheprimitive,microscopicorganismslikeprotozoa,bacteria,algaeandfungi,underit.

Fig6.2Paramecium Fig6.3Agaricus (Fungus)(Protozoa)

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Four kingdom classificationThedevelopmentofmicroscopeandelectronmicroscopeinparticular,

revealedanimportantdistinctionbetweenorganismscontainingcells,withoutadefinitenucleus(prokaryotes)andorganismscontainingcellswithadefinitenucleus (eukaryotes).Toaccommodate,prokaryotes,Copelandaddedanotherkingdomcalled‘Monera’andproposedfourkingdomclassificationin1966.Heincludedbacteriaandoneofthemostprimitivealgae,calledbluegreenalgaeunderthiskingdom;because,bothofthemexhibitprokaryotictypeofcells.Blue,greenalgaeareplacedunderadivisioncalledCyanobacteria.ThefourkingdomsintroducedbyCopelandare–monera, Protista, Plantae and Animalia.

Fig6.4BacteriumFig6.5Nostoc(bluegreenalga)

Five kingdom classification Plants prepare their own food. But fungi, unlike plants do not

prepare their food. Thus, the difference between fungi and otherplantswas recognized, byRobert Whittaker. He created anotherkingdom,‘mycota’,in1969andincludedfungi,underit.Thissystemofclassificationisnowwidelyaccepted.ThekingdomsintroducedbyRobertWhittakerareMonera, Protista, Plantae, Animalia and mycota.

Know this : WhittakerrevisedthekingdomProtistaandplacedonlysinglecelledeukaryoticorganismsunderthisgroup.

Wehaveunderstoodtheneedforthedevelopmentoffivekingdomclassification.Haveweconsideredalltheorganisms?Aretheregroupsnotincludedinanyofthesekingdoms?Yes,thereare;theyareviruses.Virusescreateaspecialprobleminclassification.

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Fig6.6Fivekingdomsoflivingorganisms

Virusesdonothaveacellularstructureandhence theyarenotconsidered as organisms. They cannot be included either underprokaryotesoreukaryotes.Hence,virusesformaseparate living entity.Have you heard about the viruseswhich attack plants? animals?bacteria?Doyouknowthevariousdiseasescausedbyviruses?

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Exercises :

I. Four alternatives are given to each of the following incomplete statement/question. Choose the right answer :

1. Akingdomconsistingofsinglecelled,prokaryoticorganismsis

a.mycota b.monera c.plantae d.protista

2. Whichoneofthefollowingisthebasicunitofclassificationofthelivingorganisms?

a.family b.species c.genus d.kingdom

3. Mostprimitiveorganisms,amongthefollowingare

a.Monerans b.Protists c.Fungi d.Algae

4. Whichoneofthefollowingshouldbegroupedwithwhales,accordingtomodernClassification?

a.Shark b.Dolphin c.Snake d.Tortoise

II. Fill in the blanks with suitable words

1. Plantswithmanywoodystemsarecalled_________________.

2. Animalswithoutabackbonearecalled_________________.

3. Mostoftheorganismsdependdirectlyorindirectlyupon__________forfood.

4. Group of organisms, that breed among themselves and producefertileoffspringsmakea___________.

III. Match the following

A B

1. familiaris a.class

2. primate b.genus

3. anacardiaceae c.species

4. magnoliophyta d.order

e.family

f.phylum

g.kingdom

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IV. Answer the following 1. Whyareanimalsincludedundereukaryotes?

2. Inwhichkingdomdoyouincludemulticellular,eukaryote,primitive,eterotrophicorganisms?

3. Aristotle’s classification include both fish and whale under onegroup.Howaretheseunrelated?

4. What is thedifferencebetweenplantsandanimalswith regard tonutrition?

5. Place the following organisms in their respective kingdoms. deer,paramecium,mushroom.

6. Howcanyouplayanimportantroleinconservingnaturalresourcessuchasplantsandanimals?Explain.

7. Whichoneofthefollowingisaprokaryotecell?Why?

A B

V. Suggested ActivitiesActivity 1

Divide the class into three groups A, B, and C. Each group should collect the scientific names of five familiar organisms. ‘A’ group for protists, ‘B’ group for kingdom plantae and ‘C’ group for kingdom animalia.

Activity 2

Observe and list out the various kinds of animals around you. Classify them into vertebrates and invertebrates.

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CHAPTER 7

THe wOrLD OF MICrOBeS

After studying this chapter students : • statethemeaningofmicroorganisms.

• recordobservationsmadeusingmicroscope.

• developtheskillofpreparingmicroscopicslides.

• comparethecharacteristicsofdifferentgroupsof

microorganisms.

• reasonouttheneedtobehygienic.

Youfindsomanythingsaroundyou.Ofthosesomearelivingandothers are non living things.Of the living things, youfind varietiesof plants and animals. Yet there are somany organisms whichcannotbeseenthroughournakedeyes.Theseorganismsarecalledmicro organisms. You have read about classification of bacteria,protozoa,fungi,algaeandvirusinanearlierchapter.Allthesearemainlymicroorganisms.

Activity 7.1

Take a small sample of curd. Put a drop of curd on a microscopic slide. Spread the curd drop evenly. Dry the curd smear. Add methelyne blue stain on to the curd smear. Remove excess of stain by washing the slide with water. Now observe the slide under a compound microscope, under oil immersion magnification. What do you observe? Tiny rod like objects which you see are the microorganisms, which have converted milk into curds.

Fromtheaboveactivityitisclearthatmicroorganismscanbeseenonlythroughpowerfulmicroscopes.

Know this : In lightmicroscopy,oil immersion isatechniqueusedtoincreasetheresolutionofamicroscope.Thisisachievedbyimmersingboththeobjectivelensandthespecimeninatransparentoilofhighrefractiveindexsuchaslinseedoil.

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MicrobiologistFig7.1Lactobacilli

Fromwheredidthesebacteriacomeintocurd?Itisobviousthattheyhaveappearedfromthepre-existingbacteria.Thereisafamoussayinglifebegetslife.Letusunderstandthisbyanactivity.

Activity 7.2

Take a bowl of milk. Add a spoon or two of curd into it. Leave this bowl as it is for about eight to ten hours. Now what do you observe? Milk is converted into curds. You can repeat the activity mentioned above taking this curd sample. What do you conclude? You might wonder whether milk did not contain any curdling bacteria. To answer this, let us consider another activity.

Activity 7.3

Take a conical flask whose mouth is plugged with cotton. Keep this conical flask in a pressure cooker. Heat this under pressure just like you cook food using a pressure cooker. Light two spirit lamps which are kept on a table. Place the conical flask between the two spirit lamps. Carefully pour some milk into the conical flask. The milk should be pasteurized and tetra packed. This is easily available in the market. Put a drop of this milk on to the microscope slide. Spread it evenly. Dry the smear. Add a drop or two of methelyne blue stain. Wash excess of stain by water. Now observe the slide under a compound microscope under oil immersion magnification. Do you observe any bacteria?

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Now add a spoon or two of curd into milk sample. Leave this for about 6 – 7 hours. Repeat activity 7.2 What is your inference? Don’t you think life begets life?

ThiswasexperimentallyprovedbyLouisPasteurbyhis famousswan neck flask experiment.ItisevidentfromPasteur’sexperimentandalsofromtheaboveactivitythatlife arises from pre existing life itself.Inearlierdaysitwasbelievedthatlifeemergedspontaneously,fromothernonlivingobjects.ButPasteur’sswanneckflaskexperimentthedisprovedthisandestablishedtheoryofbiogenesis.

Think : Whywastheconicalflaskheatedinapressurecooker?

Whywastheconicalflaskplacedbetweenthetwoburningspiritlamps?

Fig7.2SpirilliBacteria

You have observed the bacteria present in curd. What wastheir shape? How do they really look ? Now look at figure 7.1,they are rod shaped. Rod shaped bacteria are calledbacillus. ThebacteriathatyouhaveobservedinthecurdsampleareLacto bacilli. Aretherebacteriaofdifferentshapes?Yes,somearespherical,somearecommashapedandsomearespiral.

Sphericalbacteriaarecalledcocci.Byobservingthefigure7.2wecanknowthatcoccibacteriamaybesingle,inpairs,inclustersandinchains.Commashapedbacteriaarecalledvibrio.spirallycoiledbacteriaarecalledspirilli.

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Fig7.3TypesOfCocciBacteriaFig7.4Structureofatypicalbacterium

Lookatthefigure7.4wecanunderstandthestructureofbacteriawithitshelp.Youarestudyingthestructureofatypicalbacillus.Thebacteriumhasanoutermostlayercalledcellwall.Nexttothecellwallyoucanobservetheplasmamembrane.Plasmamembraneenclosescytoplasm. Youmay recall that the geneticmaterial of a bacteriumisnot enclosedbyanuclearmembrane.Suchorganismsare calledprokaryotes.Flagellahelpthebacteriumtomove.

Thereisalayerexternaltothecellwall.Thisiscalledthecapsule.Thickerthecapsulemorewillbeitsdiseasecausingability.

Think : Aretherenonmobilebacteria?

Think : Bacteriadonotcontainanymitochondria.Howisenergyreleasedinthem?

There is a groupof viruseswhich infectbacteria. Theseare thebacteriophages. Bacteriophage is a virus. You have already learntthat viruses are living entities. Letusnow study the structure of abacteriophage.

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Fig7.5BacteriophageFig7.6H.I.V.

Lookatthefigure7.5.Abacteriophagehasaheadregioncontaining

thegeneticmaterial.ThegeneticmaterialofabacteriophageisDNA.Thecollarregioncontainsproteinsheath.Lookatfigure7.6howisthisvirusdifferentfromabacteriophage?Aretheredifferenttypesofviruses?Arethereviruseswhichinfectplantsandanimalsincludinghumans?

Think: Canbacteriophagesbeusedtokillbacteria?Cantheyreplaceantibiotics?

Fig7.7Amoeba

Hereisastudentwhoisobservingadropofstagnantwaterunderacompoundmicroscope.Heobservesanorganism.Hedrawsthefigureof

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thatorganisminhisnotebook.Itappearsjustliketheoneshowninthefigure7.7.Hetakesthehelpofhisteacherandidentifiesitasamoeba.

YouknowthatAmoebaisincludedunderthekingdomProtista.Itisaprotozoan.Amoebahasanexternalmembranecalledthecellmembrane.Unlikebacteriaithasanucleuscoveredbyanuclearmembrane.Alsoithasorganelleslikemitochondriaandvacuole.Theseorganellesarefoundinthecytoplasm.

Thecellmembraneallowsmaterialstodiffuseinandoutofthecell.Amoebamoveswiththehelpofpseudopodia.Pseudopodiaalsohelpsamoebatoengulffood.Foodisdigestedinthefoodvacuole.Contractilevacuolehelpsinexcretingexcesswaterandwastes.

While observing amoeba, a student also came across anotherorganism.Hehasdrawnthediagramofthesameinhisnotebook.HelaterrecognizeditasChlamydomonas,analgabelongingtoKingdomPlantae.Youcanobservethediagramofthatorganisminfigure7.8.

Fig7.8Chlamydomonas

HereisAnusha,astudentofeighthstandard.Shelearnssciencebyconductingexperimentsandthroughactivities.Shehascutalemonintotwohalvesandkeptitexposedtoair.Afterabout48hours,shefindsabushymaterialonthefleshysideoflemonpieces.Shepreparesawetmountofthebushymaterialandobservesitunderacompound

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microscope.Sherecognizesthatitisblakishincolour.Sheinfersthatitdoesnotcontainchloroplast,likeChlamydomonas.Shealsoinfersthatitisafungus,calledAspergillus.

Fig7.9FungusgrowingonLemonFig 7.10 Aspergillus

Fungibelong tokingdomMycota.Helpher recall thecharacteristicfeaturesoforganismsbelongingtothiskingdom.Activity 7.4

Make a suspension of yeast using yeast powder and water. Yeast powder is easily available in market. Take a drop of this suspension and prepare a smear on a microscopic slide. You can stain the smear using methelyne blue or saffronin stain. Observe the smear under a compound microscope. An enlarged figure of yeast cell is given below. You can compare this with the yeast cell that you have observed.

Observe the yeast cell and explain the structure of yeast taking the help of your teacher.

Fig7.11Yeast

Most of themicroorganisms are useful to us.Microorganismsareusedinfoodindustry,leatherindustry,dairyindustry,pharmaceuticals,watertreatmentplantsandeveninsewagetreatment.Microorganisms play a very important role inagriculture.Recallthatmicroorganismsplayanimportant role in ecosystems as decomposersHoweversomemicroorganismsareharmfultoo.Theyspoilfood.Theyalsocausediseasesinplantsand animals. You will learn regarding plantdiseases in a later chapter. The following tablekeeps you informed on some of the commonmicrobialdiseasescausedinhumans.

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Table 7.1 Some common human diseases caused by microbes

Name of the

disease

Disease causingmicrobe

Symptoms mode of transmission

Preventive measure

Influenza InfluenzaVirus

Chills,fever,sorethroat,cough,musclepains,severeheadache,

Air,Contaminatedhandkerchiefs,

Avoidbeingclosetoinfectedpeople,Donottouchthenoseandeyeswithcontaminatedhands.

Cholera VibrioCholerae

Vomiting,diarrohea,dehydrationstomachpain

Contaminatedwater,food

Avoidingeatinganddrinkingcontaminatedfoodandwater.Vaccination.

Malaria Plasmodium vivax

Recurringfever,chills,headache,musclepain,tiredness,stomachpain,nausea,vomiting

Biteoffemaleanophelesmosquitoes

Vaccination,controllingmosquitopopulation,usageofmosquito curtainsareadvised.

Aspergillosis Aspergillus niger

Cough,fever,chestpainanddifficultyinbreating

spreadsbyinhalingsporesofaspergillusniger

Avoiddustyandunhygienicplaces.

Youcanlistafewmoremicrobialinfections.Microorganismsarebeneficialtousasstatedearlier.However,ifweneglecthygiene,thenwearepronetomicrobialinfections.vaccines usuallypreventspecificmicrobialinfections.Avaccinetypicallycontainsanagentthatresemblesadisease-causingmicroorganism.Itisoftenmadefromweakenedorkilled formsof themicrobeor its toxins.Thevaccinestimulates thebody’simmunesystemtorecognizethemicroorganismoritstoxinorsometimesbothasaforeignsubstance.Body’sdefencesystemdestroysitandpreventsanyfurtherinfectionfromthesamemicroorganism.ThecreditofdevelopingthetechniqueofvaccinationgoestoscientistssuchasEdwardJenner,LouisPasteur,JosephListerandothers.

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Activity 7.5

Collect information from various sources on the inventions of vaccines. Enact a drama on this subject on the occasions like school day science club activities.

Activity 7.6

Prepare a vaccine chart, taking the help of your parents and family doctor.

Exercises :

I. Four alternatives are given to each of the following incomplete statement /question. Choose the right answer :

1. Oneofthefollowingdoesnotbelongtothegroup

a. Aspergillusniger b. Clostridiumtetani

c. Staphylococcusaureus d. Vibriocholerae

2. Thelocomotorystructureofamoebais

a. cilia b. flagella

c. pseudopodia d. tentacle

3. Chlorophyllispresentin

a. Chlamydomonas b. Mushroom

c. Yeast d. Aspergillus

II. Fill in the blanks with suitable words1. Biogenesiswasestablishedby__________________.

2. Malariaiscausedby___________________.

3. Vibrioare______________________shapedbacteria.

III. Answer the following1. Whataremicroorganisms?

2. Explainthestructureofatypicalbacillus?

3. Drawadiagramofatypicalbacillusandlabeltheparts?

4. Howcanthetransmissionofcholerabeprevented?

5. Whatarevaccines?

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CHAPTER 8 DeSCrIBINg MOTION

After studying this chapter students :

• distinguishbetweendistancetravelledanddisplacement.

• calculatedistancetravelledanddisplacement.

• definethetermsspeed,velocityandacceleration.

• distinguishbetweenuniformandnon-uniformvelocity

• representgraphicallyvelocityandacceleration.

• solvenumericalproblemsonvelocityandacceleration

There is a popularKannada poemwritten byN.R.Hiremath onmoon. The poem starts like this “Why is themoon running awayAmma? Is he afraid of the clouds? [“Chandiranetake oduvanammamodakebedarihane......’’].Youmighthaveexperiencedthesame.Whenthebrightmooninthenightskyisapparentlycoveredbythincloudsandwindblowingacrosstheclouds,themoonappearstoberunning.Whathappenswhentherearenoclouds?

Imaginethatyouaresittinginsidethetrain.Whenthetrainstartsmovingyoufeelthatthepersonsontheplatformaremovingbackwards.Youfeelthatyouandtheotherpersonsinsidethetrainarenotmoving.Butforapersonstandingoutsidethetrain,thefeelingwillbethatthetrain,youandtheothermembersinsidethecompartmentareallmoving.

Aboveexperiencesshowthatmotionisonlyrelative.Canyourecallsomemoreexperiencesaboutrelativemotion?Isrestalsorelative?

Anobjectissaidtobeinmotionifitspositionchangeswithtime,withfixedframeofreference.

Do you Know ?

Restandmotionarerelativeterms.Apenkeptonthetableisatrestwithrespecttothetable.ButyouknowthatEarthisrotating.Theobjectskeptonearthmustalsobemovingwiththeearth.

Inthischapteryouwilllearnmoreaboutmotion.

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Distance and displacementConsidertwoflowers‘A’and‘B’onthesametree.AHoneybeeflies

fromAtoBinacurvedpathasshown.infig8.1

Fig8.1

ThelengthoftheactualpathithastravelledfromAtoBisthedistance.TheshortestdistancebetweenAandBisdisplacement.Displacementreferstodistancetravelledinagivendirection.Ifthehoneybeestartsfrom‘A’reach‘B’andagaincomesbackto‘A’,thedistancetravelledwillbedifferentfromdisplacement.Howeverdisplacementiszero.Whenwillbethedistancetravelledanddisplacementsame?Displacementreferstochangeofposition.TheS.Iunitofbothdistancetravelledanddisplacementis metre.Ifthedisplacementis30metreitiswrittenas30m.

Activity 8.1

Take a railway map of India. Using a thread and scale find the displacement from Bangalore to Delhi. Also find the distance travelled by the train from Bangalore to Delhi. Which is shorter? Can you think why?

Activity 8.2

Fig8.2

AnobjecttravelsfromAtoBandthenfromBtoCasshowninthefigure8.2.Whatisthedistancetravelled?Whatisthedisplacement?

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AnobjectmovesfromAtoBinacircular

Fig8.3

path of radius 7m.What is the distancetravelled?Whatisthedisplacement?Displacement=Diameter =2×radius =2×7=14mDistancetravelled= ×Circumference

speed and velocity

Youmighthaveseensignboards,“speedlimit30kmperhour”,neartheschoolorhospitalzones.Youmighthaveobservedwritingsinsideabus“maximumspeed60kmperhour”.Whatdothesewritingsindicate?

Abusmaybesloworfastduringitsjourney.Whatdoyouunderstandbythewordsfastorslow?

Ingeneralspeedisthedistancetravelledbyanobjectinunittime.

Letustakeanexample.Abuscoversadistanceof30kminonehour.Inthenextonehouritcoversthedistanceof50km.Thetotaldistancetravelledwillbe30+50=80km.Totaltimetakentocoveradistanceof80kmis2hours.

Averagespeed= TotaltimetakenTotaldistancetravelled

= =40kmperhour

Thetermaveragespeedisusedbecausespeedinreality,willnotbethesame.Thetermspeeddescribes‘fast’and‘slow’motionsinrelativecontext.TheSIunitofspeedisms-1(metrepersecond)

Motioncanbeuniformornonuniform.Inpracticalcaseswecomeacrossnonuniformmotion.Similarlyifanobjectcoversequaldistancesinequalintervalsoftime,itissaidtohaveuniformspeed.Weusethetermaveragespeedfornon-uniformmotions.

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Activity 8.3:

An object covers a distance of one metre during first 30 seconds. After 30 second it covers a further distance of 4 metre in 15 seconds. Calculate the total distance travelled and total time taken. Calculate the average speed of the object.

Letusconsideranotherinterestingnumericalproblemaboutaveragespeed.

Abus travels from ‘A’ to ‘B’witha speedof40kmperhour. Ittravels from‘B’ to ‘A’with the speedof60kmperhour.What is itsoverallaveragespeed?Thereadyansweryoumaygettothisquestionis

240 60

2100 50+ = = kmperhour.

A

40kmperhour

60kmperhourB

Butisitcorrect?Letusanalysethisproblem.Youknowthat

Hence time taken to coveradistance fromA toBata speedof40kmperhouris

DistancetravelledfromAtoB

Speed

Inshortspeedis40kmperhour'D'isthedistance

SimilarlytimetakentocoveradistancefromBtoAataspeedof60kmperhouris

Inshort speedis60kmperhour'D'isthedistance

Hencetotaltimetaken=T1+T2=

D D D D40 60 120

524

+ = = T o t a l

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distancetravelled=D+D=2DHenceaveragespeedofthebus=

Activity 8.4

50kmperhour 60kmperhour

100km 180kmA CB

An object moves from ‘A’ to ‘B’ covering a distance of 100 km with a speed

of 50 km per hours. It covers a further distance of 180 km from B and reaches

C with a speed of 60 km per hour. What is the average speed of the object?

Ans : 56 km per hour.

Letusimagineanothersituation.Anobjecttravels5kmperhour.Aftertwohourswhatisthedistancetravelled?Itis10km.Butwecannotsaytheexactpositionoftheobject.Wecansimplysaythattheobjecthascovered10km.Ifthespeedismentionedalongwithdirectioninwhichitmoves,thenitispossibleforustodecidethepositionoftheobjectwithrespecttoinitialpositionaftercoveringadistanceof10km.Thetermvelocityisusedtodescribethemotionswhichrefertospeedaswellasthedirectionofmotion.

Velocityistherateofdisplacementofanobjectinunittime.TheS.Iunitofvelocityismetre per second.Itisexpressedasms-1.Itisourcommonpracticetousethetermsspeedandvelocitywiththesamemeaning.Buttheyaredifferent.

example: Anobjectismovinginacircularpathofradius7m.Totravelfrom‘A’to‘B’alongthecircumferenceittakes2secondwhatisitsaveragespeed?

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Fig8.4

Speed=distancetravelled=halfofthecircumference

timetime

Speedandvelocitycanbeequalforuniformmotionsalongastraightline.

Fig8.5

ImaginethatabusismovingwithuniformspeedfromEasttoWest.YoumaysaythereisdirectionfromEasttoWest.Whycan’tweusethewordvelocityinsteadofspeed?Rememberatanypointoftimeduringitsjourneyfrom‘A’to‘B’,thebusischangingitsdirection,andalsothespeeddependingupontheroadconditions.Thecorrectwordtodescribethemotionofthebusisspeedoraveragespeed.Activity 8.5

An object ‘A’ is moving in a circular path with ‘O’ as centre along the circumference. What will be the direction of its velocity at the positions ‘B’ and ‘C’?

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Fig8.6Objectmovingincircularpath

Activity 8.6

Observe the sparks coming out of a knife sharpening wheel. In which direction will the sparks move?

Youmighthavecomeacrosstheword‘accelerator’whichisusedbypeopleusingautomobiles.Whatisit?Itisusedforchangingspeed.Thatis,itisusedtodecreaseorincreasethespeedoftheautomobile.

Imagine that youhave come to a railway station to say ‘happyjourney’toyourfriendwhoissittinginsidethetrain.Whenthetrainstartsmovingitwillbeslow.Imaginethatinthefirstminuteitsaveragespeedis10kmperhour.Itsaveragespeedwillbecome20kmperhourinthesecondminute.Inthethirdminuteitsaveragespeedwillbecome30kmperhourandinthefourthminuteitwillbe40kmperhourandmoreorlessmayremainthesameafterwards.Here,everyminutethespeedofthetrainischangingattherateof10kmperhour,perminute.Itcanhappenagainstthedirectionofmotionalso,asinthecaseofatrainapproachingastationbeforecomingtorest.

Changes inmotion such as above are described by the termacceleration.Thetermaccelerationisusedbecauserarelywecomeacrossuniformmotion or uniform speed or uniform velocity in ourdailylife.Accelerationalsoneednotbeuniform.Itisusualpracticeincalculationstoconsideritasuniform.

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The conceptwhich indicates thenature of change in velocity isacceleration.It can be defined as the rate of change of velocity or change in the velocity of anobject in unit time.ItsS.Iunitismetrepersecondpersecond.Itisexpressedasms-2.

Find out : Imaginethatanobjectismovingatauniformspeedinacircularpath.Thoughthespeedisuniform,itiscontinuouslyaccelerated.Why?

Find out : Imagine that an object moving with a uniform velocity of7ms-1doesnotchangeitsvelocityforatleast10seconds.Whatwillbeitsaccelerationduring10seconds.?

example : Anobjectatrestgainsanaveragevelocityof40ms-1in5seconds.Whatwillbeitsacceleration?

Itsinitialvelocityiszero.Itsvelocityafter5secondsis40ms-1.

Timetakenbyittochangeitsvelocityfromzeroto40ms-1isfiveseconds.

Thereforetherateofchangeofvelocity= =8ms-2 accleration=8ms-2

Think : Achildthrowsaballupwards.Itgoesup,appearstostopandthenstartsfallingdown.Isthismotionanexampleforacceleratedmotion?Givereasons.

equations of motion: If you are interested, try to know theequationsofmotionofobjectsmovinginastraightline.Theyareusefultocalculatevelocity,acceleration,timeanddistancetravelled.Theyaregivenhereforyourreference.

Theequationsare

Thesymbolsusedare:‘u’forinitialvelocity‘v’forfinalvelocity‘t’fortime‘s’fordistance

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example: 1

Anobjectatreststartsmovingandattainsavelocityof10ms-1

after5seconds.Whatistheacceleration?

Initialvelocityu=0(rest)

Finalvelocityv=10ms-1

Timeintervalt=5seconds

Thereforea

Considertheoppositeoftheaboveexample

Anobjectmovingwithauniformvelocityof10ms-1comesto

restafter5seconds.Whatistheacceleration?

Initialvelocityv=10ms-1

Finalvelocityu=0

Timeintervalt=5s

Accelerationinthisexampleisagainstthedirectionofmotion.

example 2 An object at rest startsmovingwith uniform acceleration of

1ms-2.Calculatethedistancetravelledbyitin4seconds.

Initialvelocityu=0accelerationa=1m s-2

Timeintervalt=4seconds

Distancetravelled=s=ut+½at2

s=0×4+½×1×42

=0+½×1×16

=8m.

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example 3 An object starts from rest and attains a uniformaccelerationof4ms-2.Whatwillbeitsvelocityattheendofhalfametre?

u=0a=4ms-2 s=½mv=?

v2=u2+2as

v2=02+2×4×½

v2=4

v=√4

=2ms-1

graphic representation of motion

Motioncanberepresentedbyline

graphs. We can also obtain certain

desired information from the graphs.

Hereareafewsimpleexamples.

example 1 :Distance-timegraph

situation 1 : Let us consider a bodywhich is covering equal distances in

equal intervalsof time. Ifwerepresent

timeonthex-axisanddistancetravelled

on the y-axis, wewill get a graph as

showninthefigure.

Fromthisgraphwecanfindoutthedistanceatwhichthebodyisat

presentfromitsstartingpoint.Timetakentocoveradefinitedistance

canalsobedeterminedfromthegraph.Sinceitisuniformmotionwe

canalsoknowthespeedofthebody.

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find the following from the graph.

• What is the distance travelledbythebodyin15seconds?

•Whatisthetimetakenbyittocoveradistanceof6m.

•Whatisthespeedofthebody?

situation 2 : Letus considerabodywhichiscoveringdifferentdistancesinequal intervals of time. The resultinggraphwillresembletheoneshowninfigure8.8.

Find the following from the graph

• Whatisthedistancetravelledbythebodyin20sec?

• Whatisthespeedofthebodyinfirst10sec?

• Whatisthespeedofthebodyinsecond10sec?

•Whatistheaveragespeedofthebodyin30sec?

note : If the motion of a body in a straight line is in a particulardirection, thenumericalvalueofvelocity issameasthatof thespeed.Thereforeinsuchcaseswecanalsofindoutthevelocityfromthegraph.

example 2 :Velocity-timegraphorspeedtimegraphofthebodymovinginastraightlineinaparticulardirection.

situation 1 :Considerabodymovinginaparticulardirectionwithuniformvelocity.Atanyunittime-intervalthevelocity of such a body does notchange.ItmeansthattheaccelerationisO.IfitdenotetimeontheX-axisandvelocityontheY-axis,wegetagraph like the one shown in thefigure8.9.Whatisthevelocityofthebodyinmotionasrepresentedbythegraph?Whatisitsacceleration?

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situation 2 :Considerabodymovinginaparticulardirectionwithauniformacceleration.Thegraphofsuchamotionmaybeoneofthetwovarietiesshownin the figure 8.10. Identify the graphrepresentingaccelerationinthedirectionofmotion and the one representingaccelerationinoppositedirection.

Exercises :

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer :

1.Uniformcircularmotioniscalledcontinuouslyacceleratedmotionmainlybecause,

a.directionofmotionchanges

b.speedremainsthesame

c.velocityremainsthesame

d.directionofmotiondoesnotchange

2.Acricketerhitsasixer.Thecricketballmovesupwithavelocityof2ms-1andfallsdown.Itsinitialvelocitywhilefallingdownwillbe

a.1ms-1 b.1ms-2 c.0ms-1 d.2ms-1

II. Fill in the blanks with suitable words

1. SIUnitofaccelerationis______________________.

2. Velocityhasbothspeedand______________________.

3. Ifanobjectstartsfrom‘A’andcomesbackto‘A’,itsdisplacemontwillbe_________________________.

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iII. Solve 1. An object is moving in a circular path of radius 3.5 m. If it

completesonefullcycle,whatwillbethedisplacementandwhatisthedistancetravelled?

2. Anobjectchangesitsvelocityfrom30ms-1to40ms-1inatimein-tervalof2seconds.Whatisitsacceleration?

3. An object at rest starts moving. It covers a distance of 2 min one second. It covers a further distance of 5 m in twoseconds in the same direction. What is its average velocity andacceleration?

IV. Answer the following1. If a body ismoving with uniform velocity in a given direction its

accelerationwillbezero.Why?

2. Distinguishbetweenspeedandvelocity.

3. Distinguishbetweendistancetravelledanddisplacement.

4. Whatareuniformandnon-uniformmotions?

5. Whilementioningaccelerationthetimeismentionedtwotimes.Why?

V. extended activity Representthefollowingmotionbyagraph.

Velocityms-1 40 30 20 10

Timesecond 1 2 3 4

1. Findtheaccelerationfromthegraphand

2. Findthetimetakentotraveladistanceof35mfromthegraph.

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CHAPTER 9

FOrCe AND NewTON’S LAwS OF MOTIONAfter studying this chapter students :

• statetheeffectsofforce

• distinguishbetweenbalancedandunbalancedforces

• definethetermmomentum

• stateNewton’slawsofmotion

• solvenumericalproblems

• giveillustrationsforinertia

• giveillustrationsforthesecondandthirdlawsofmotion

Intheearlierchapteryouhavestudiedaboutmotionoftheobjects.Amarbleatrestcannotmoveuntilitispushed.Thereisanexternalphysicalquantityofenergythatmakesthemarbletomove.Similarlyamovingmarblecanalsobestopped.Afastmovingbuscanbemadeslow.Itispossibletochangethespeedofautomobileswheneverrequired.Thephysicalquantitythatwearereferringtoisforce.Thewordforceisusedinourdailylifeunderdifferentcontext.Considerthefollowingstatements“thecricketerwouldhavescoredasixerifheweretohittheballwithagreaterforce”.

“Ifthefootballplayerhadkickedtheballwithagreaterforcehewouldhavescoredagoal”.Inthesetwoexamplesthereisreferencetotheamountofforce.

forceisaphysicalquantitythatchangesthestateofrestofabodyorthatchangesthevelocityofabody.

Whataretheotherareasinwhichweusethewordforce?

Magneticforceandgravitationalforce,aretwoexamples.Canyougivetwomoreexamples?

Activity 9.1

Take a rubber ball. Press it with both of your palms. The force shows a visible effect on the ball. Press a leather cricket ball. You will not see any visible effect on the ball. Why?

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Forceappliedonanobjectcan• changethevelocityofanobject• changetheshapeofanobject.Intheactivityof9.1whenyoupressacricketballyoucanonly

feelthatyouareapplyingforce,butnovisiblechangeisobservedwithrespecttotheball.

Letusconsideronemoreexample.Inatugofwarwhenthetwoteamspullitwithequaleffort,the

ropeandthetwoteamsremainstationary.Whathappenswhenoneoftheteampullsthetugharder?Thiscircumstanceindicatesunbalancedforces.Howdoyoudefineunbalancedforces?

Theeffectofforcewillbeobservedwhenunbalancedforcesactonanobject.Unbalancedforcesactingonanobject,changeitsspeedordirectionofmotionorboth.

Iftwoormoreforcesactingonthesameobjectkeeptheobjectinequilibriumpositionorinthesamestate,thentheforcesarebalancedforces.

Imagineacaratrest.Itcanbepushedbyagroupofthreeorfourpersons.Ifthecarispushedthenitstartsmoving.Itsspeedordirectionofmotiondependsupontheforceandthedirectionofapplicationofforce.

Continuousapplicationofforceisnecessarytomaintainthemotionofanobject.Isittrue?

Amarblepushedbyyoustartsmoving,slowsdownandfinallystops.Inthiscasefriction force,thatisfrictionbetweenthemarbleandthesurfaceonwhichitismovingthatstopsthemarble.Whatwillhappenifthereisnofriction?

GalileoGalilei

galileo galileiGalileoopposedtheideaofGreekphilosophers

that a moving body comes to rest when noforcesact on them.Galileo’swork inspiredSir.IsaacNewton,whoproposedthelawsofmotionsystematically.

SomeexamplesofmotionstudiedbyGalileoaregiveninthefollowingdiagrams.

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BallmovingdownonBallmovinginahallowinclinedplanehemisphere

Motionofapendulum

Fig9.1Studiesofgalileo

Brief biography of Sir. Isaac Newton. [ 1643-1727 ]

Sir.IsaacNewton

IsaacNewtonwasaphysicist,mathematician,astronomer andnatural philosopher.Hewasoneofthemostinfluentialpeople.Thefamousmathematicsbook“PrincipiaMathematica”waswritten by him. He developed a branch ofmathematics “calculus”. The First reflectingtelescopewaspreparedbyhim.Hedemonstratedvisiblespectrum.

Hisideaaboutlightasstreamofparticlesorcorpuscleshasaminorresemblancetophoton

theoryandquantumtheory.HewasthePresidentofRoyalSocietyofLondonin1703.HewasmemberoftheparliamentofEnglandin1689to1690andin1701.Henevermarried,beinghighlyengrossedinhisstudiesandwork.Hewasreligiousbutunorthodox.Hewasmodestofhisachievements.ThefamousstatementofNewtonis“IfIhaveseenfurther,itisbystandingontheshouldersofgiants”.

Iamasmallboypickinguppebbleshereandthereontheseashoreofknowledge.

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newton’s Laws of motion:

Sir. IsaacNewton studied themotion of objects and the factorsrelatedtothechangeinvelocity.Heidentifiedcertainrelationshipsandstatedthemintheformoflaws.Letusknowmoreabouttheselaws.

inertia:

While travelling inabusyoumighthaveexperiencedthatwhenbrakesaresuddenlyapplied,youleanforward.Whenthebusstartsmovingyouleanbackward.Why?

Fig9.2Inertiaexperiencedinamovingvehicle

Whenwearesittinginsideamovingbus,ourentirebodywillalsobemovingwiththespeedofthebus.Whenbrakesaresuddenlyapplied,thebuscomestorest.Thepartofthebodythatisincontactwiththebusalsocomestorest.However,thepartofourbodywhichisnotincontactwiththebushasatendencytomoveinthedirectionofthebusbeforecomingtorest.Soweleanforward.Similarlywhenabusatreststartsmovingthepartofourbodywhichisnotincontactwiththebushasatendencytoremainatrest.Soweleanbackward.

Activity 9.2

You need a glass tumbler and a square shaped cardboard piece from an old invitation or greeting card to perform this simple experiment. Place the card board on the glass tumbler as in figure No: 9.3 . Place a rupee coin on the cardboard. Flip the cardboard with your fingers.What is your observation?

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Fig9.3Inertia

Activity 9.3

When the pawns in a carrom board game are arranged vertically and the bottom pawn is hit by the striker the pawn at the bottom gets removed and the vertical arrangement of the pawns remains intact. Try to recall your other experiences while playing a carrom board game. The tendency of the objects to remain at rest or in state of motion when no forces act on them is called ‘inertia’. This is stated as Newton’s first law of motion. “Every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed on it”. Newton’s first law of motion is based on the inventions of Galileo. It is also called law of inertia.

The first law of motion has the following point. To accelerate an object an external unbalanced force is necessary. That means, to change the state of rest or state of motion of an object, an unbalanced force must act on it.

Theresistancetochangethestateofmotiondependsuponthemassoftheobjects.Itiseasiertochangethevelocityoflighterobjectsthanofheavierobjects.Massiveobjectshavemoreinertiathanlighterones.Infactmassisameasureofinertia.

Activity 9.4

Two Iron spheres of 2 kg and 5 kg each are dropped from the same height into a sand pit. Which of these two causes deeper sand pit? What happens if the 2 kg Sphere is thrown with a greater speed instead of dropping it?

Force,velocityandmassareallconsideredincomparisonwiththeactivity9.4.

Itisdescribedinthesecondlawofmotion.

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newton’s second law of motion“Theaccelerationgiventoabodybyaforceappliedtoitisdirectly

proportionaltotheforceandisinthesamedirectionoftheforceandinverselyproportionaltothemassofthebody”.

Letthemassofabodybe‘m’,lettheresultantforceactingonitbe‘F’anditsaccelerationbe‘a’.AccordingtoNewton’ssecondlawofmotion,

1.Accelerationinthedirectionofforceisdirectlyproportionaltothe

force.

∴ aaF------(1)

2.Accelerationisinverselyproportionaltothemass

∴aa ------(2)

Bycombining(1)and(2)

Wegetaa

Ora=

here‘K’isaconstant.

IfS.Iunitofmassis1kgandS.Iunitofaccelerationis1ms-2thenthevalueof‘K’willbecomenumericallyone.ThenwecanmathematicallystateNewton’ssecondlawofmotionasF=ma

Unitforceisthatforcewhichproducesanaccelerationof1ms-2inamassof1kg.

S.Iunitofforceiskgms-2ornewtonorN.

example 1.Calculatetheforcerequiredtochangethevelocityofanobjectofmass4kgfrom2ms-2to4ms-2inonesecond.

Solution:F=ma

m=4kg,a=2ms-2F=?

F=4kg×acceleration

F=4×2

=8kgms-2or8newtonor8N.

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Example 2.Anobjectofmass10kgismovingwithinitialvelocityof2ms-1.Tomakeitcometorestinonesecond,whatshouldbetheunbalancedforce?

Solution:initialvelocity=2ms-1

Velocityatrest=0ms-1

timeinterval=1second,massm=10kg.

Changeinvelocityinonesecondoracceleration

F=ma

F=10×-2

=-20kgms-2or-20newtonor-20N

Thenegativesigntellsusthattheforceexertedisoppositetothedirectionofmotion.

example 3.Anobjectofmass20kgismovingwithinitialvelocityof2ms-1.Ifitsvelocitychangesto4ms-1inonesecond,whatshouldbetheforceactingonit?Whatwillbethedirectionofthemotion?

Solution:F=ma

m=20kg

a= =2ms-2

∴ F=20×2

=40newtonor40N

Theobjectcontinues tomove in thesamedirectionas the forceappliedisinthesamedirection.

LetustrytounderstandNewton’sSecondlawofmotioninanotherway.

Itisourexperiencethatitiseasiertostopaslowmovingcricketballthanafastmovingcricketball.Themassofthecricketballisthesame.Itsaveragevelocitymaychange.Recalltheactivity9.4.

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Theironsphereshavedifferentmasses.Theaveragevelocityofboththespheresremains thesamewhendropped fromthesameheight.Anotherphysicalquantity“momentum”isconsideredintheseexamples.

Momentum=Mass×Velocity

OrM=mv

Momentumofanobjectisproportionaltoitsmassandvelocityorspeed.Forceisrequiredtochangethemomentumofanobject.

TheS.Iunitofmomentumiskgms-1.

Newton’ssecondlawofmotioncanalsobestatedas“rateofchangeofmomentumisdirectlyproportionaltotheimpressedforceandtakesplaceinthedirectionoftheapplicationoftheforce”.

Know this : Conservation of momentum

Momentum of a system is always conserved.What does itmean?Whenabulletisfiredfromarifle,bulletmovesfastbuttheriflealsomovesslowlyintheoppositedirectionofthebullet.Inthiscase

momentumofbullet=momentumofrifle.[lawofconservation]

Ifthemassandvelocityofthebulletare‘m’and‘v’respectivelyandifthemassandvelocityoftherifleare‘M’and‘V’respectively,

thenmv+MV=0ormv=-MV.

-MVindicatesthatriflemovesintheoppositedirectionofthebullet.

Thetwolawsofmotiontellushowanappliedforcechangesthestateofmotionofobjects.Thereisyetanotherlawofmotionwhichtellsussomethingmoreabouttheappliedforces.

Newton’s third law of motion:

“Toeveryactionthereisalwaysanopposedandequalreaction”

or

Themutualactionsoftwobodiesuponeachotherarealwaysequalanddirectedinoppositedirection.

Rememberthat‘action’and‘reaction’actondifferentbodies.

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Activity: 9.5

Take a large balloon. Fill it with air. Carefully tie a narrow tube of a discarded ball point pen to the mouth of the balloon as shown in the figure 9.4. Release the air. Air moves downwards. Balloon moves upwards. Try this with different sized balloons. Also try this with balloons of comparable masses. As the mass of the balloon increases its speed decreases . Can you think why?

Fig9.4AirballoonexperimentActivity 9.6

Observe the white stream of the exhaust of a jet plane, if you happen to spot jet planes in the sky. Observe the direction of motion of the jet plane and the exhaust fumes. What is your conclusion?

Activity 9.7

Observe the actions of a swimmer while swimming. Can you give reason for his actions?

Activity 9.8

In the traditional row boat, observe the direction of motion of the boat and the direction of motion of rowing. Can you describe this in terms of Newton’s third law of motion?

Activity 9.9

You might have observed on T.V, the launching of rockets. The exhaust gases travel with tremendous speed downwards. But the rocket that goes up will not be as fast as the exhaust gases. Can you give reason for this?

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Numerical problemAbulletofmass25gisfiredfromarifleofmass2kg.Imaginethatno

otherforcesareactingonthesystem.Ifthebullettravelswithavelocityof2ms-1,whatwillbethevelocityoftherecoiloftherifle?

solution:Momentumoftherifle=Momentumofthebullet

Massoftherifle×Velocityofrecoil=Massofthebullet×Velocityofthebullet

2×Velocityofrecoil

2×Velocityofrecoil

velocityofrecoil

AretheNewtons’lawsofmotionapplicabletocircularmotion?Youwillstudyabouttheminhigherclasses.

Exercises :I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer :

1. Actionandreaction

a.actonthesamebodyb.areequal

c.areopposite d.actondifferentbodies

2. Iftheforcesactingonanobjectarebalanced,then

a.theobjectwillbeaccelerated

b.theobjectwillbeinmotion

c.theobjectwillhavezeroacceleration

d.theobjectlosesitsshape

3. TheS.Iunitofforceis

a.Newtonsb.newtonc.newtonsd.Newton

II. Fill in the blanks with suitable words :1. Inertiaofanobjectisproportionaltoits__________________.

2. TheS.Iunitofmomentumis_________________________.

3. Tocauseaccelerationinanobjectthenecessaryfactorisunbalanced___________________________.

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4. Newton’sfirstlawofmotionisalsocalledlawof________________.

5. Thesuitcaseskeptinamovingbus,moveforwardwhenthebrakesareappliedsuddenly.Thisisdueto_________________.

III. Answer the following

1. Inatugofwargame,ifthetwoteamsexertequalforces,noneoftheteamwins.Why?

2. Whichofthefollowinghasgreatermomentum?

a.Anobjectofmass2kgmovingwithuniformvelocityof2ms-1.

b.Anobjectof1kgmassmovingwithuniformvelocityof3ms-1.

3. Whichofthefollowinghasgreaterinertia?

a.50paisecoinb.onerupeecoin c.fiverupeecoin.

4. StateanytwoillustrationsforNewton’sthirdlawofmotion.

5. Distinguishbetweenbalancedandunbalancedforces.

6. StateNewton’ssecondlawofmotion,intermsofmomentum.

IV. give reasons for the following

1. Itisdangeroustogetdownfromamovingbusevenifthebusismovingslowly.

2. Anathleteinlongjump,runsadistancebeforetakingtheleap.

3. Usuallyafielderinacricketmatch,takesacatchbymovinghishandsinthedirectionofmotionofcricketball.

V. Solve the Problems

1. Calculatetheforcerequiredtochangethevelocityofanobjectofmass8kgfrom4ms-1to6ms-1in2second.

2. Aforceof25newtonisappliedonanobjectofmass10kgmovingwithavelocityof5ms-1.Iftheobjectgainsavelocityof10ms-1,calculatethetimeinterval.

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CHAPTER 10

EnERgy And iTs foRmsAfter studying this chapter students :

• definethetermsforceandwork

• definethetermspotentialenergy,kineticenergyandpower

• giveexamplesforpotentialenergyandkineticenergy.

• distinguishbetweenpotentialandkineticenergy.

• solvenumericalproblemsonpotentialenergy,kineticenergyandpower.

• comparewaysinwhichenergyischangedfromoneformtoanother.

• describethelawofconservationofenergy.

Inafootballmatch,aplayerkicksastationaryball.Theballmovesinastraightline.Anotherplayerdeflectsthemovingballtoanotherdirection.Sometimesaplayersimplypushesthemovingballtoincreaseitsspeedwithoutchangingitsdirection.Inallthesecases,theplayersapplyforcewiththeirlegs.

force

Forceisaninfluencewhichtendstosetastationarybodyinmotionorwhichtendstochangethespeedanddirectionofamovingbodyorwhichtendstochangetheshapeofabody.

Work

Whathappenswhenforceisappliedtoamarble?Ifamarblemovesthenwesayworkisdone.Whathappenswhenforce isappliedtoawall?Ifwallisnotmovedthentheworkisnotdone.Workissaidtobedonewhenthepointofapplicationofaforcemoves.Theworkdonebytheforceonabodydependsontwofactors,magnitudeoftheforceanddistance thatthebodymoves.

Wearenowinapositiontodefineworkandsayhowitismeasured.Workdonebymovingabodyisequaltotheproductofforceexertedonthebodyandthedistancemovedbythebodyinthedirectionofforce.Thatis,Work = force Í distancemovedinthedirectionofforce.

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Unit of workYouhavestudiedthattheunitofforceisnewtonandthatofdistance

ismetre.Thustheunitofworkisnewton metrewhichiswrittenasn m.This,unitofworkiscalled joulecanbedefinedas:whenaforceofonenewtonmovesabodythroughadistanceofonemetreinitsowndirection,thentheworkisknownasone joule.

1joule=1newtonÍ1metre

1 J = 1 n mKarnatakaGovernmentissettinguppowerstationstoincreasethe

productionofelectricity.Ifthisisthenewsitwilldefinitelybeintheheadlinesofthenewspaper.Oneofthemuchdiscussedtopicstodayisenergycrisis.Ifthedemandforenergyismorethanthesupplythenitleadstoenergycrisis.

Youmaywonder,howtherecanbecrisiswhentherearesomanyformsofenergy.Heat,light,soundandsolarenergyaredifferentformsofenergy.Whenwetalkaboutenergywethinkaboutusableformsofenergy.Wethinkabouthowtotransportit,howtoconvertitintootherformsofenergy.

Think : Is the sound energy producedduring the bursting of crackersusefultous?

Canyouconvertallthesunlightwereceivefromthesunintoworkorconvertitintootherforms?

Inyourpreviousclassesyouhavestudiedaboutkineticandpotentialenergywhichareformsofmechanicalenergy.

Activity 10.1

Classify the following into kinetic energy and potential energy.

• Stretched rubber band

• Flowing water

• Compressed spring

• Water stored in a dam

• Wind

• Arrow released from the bow

Inthischapterweshallstudysomefactorsrelatedtokineticenergyandpotentialenergy.

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Activity 10.2

Conduct the activities related to kinetic energy as given in the table 10.1 Table 10.1 illustrations of kinetic energy

Sl.No.

Activities Observation Inference

1 Blow air to a paper

2 flowing water falls on a turbine(wheel)

3 Throw a cricket ball on the stumps

4 Hit the carrom coin with a moving striker

Whatdoyoufindintheaboveactivities?Themovingair,themovingball,theflowingwater,themovingstrickerarecapableofdoingwork.Allmovingobjectshavecapacity todoworkwhichmeans that theypossessenergy.Theenergythatthebodypossessesduetoitsmotioniscalledkineticenergy.

Do this : Listoutatleast5activities,whichinvolvedoingworkwithkineticenergy.

Relationship between mass, velocity and kinetic energy of an objectActivity10.3

Fig10.1

Take a wooden plank of three feet and place it on wooden block. This arrangement is called inclined plane. Mark A,B,C,D as shown in the figure 10.1 .Take a cylindrical tin of medium size(200 g) with a tight fitting lid. Fill it tightly with sand. Put an empty rectangular plastic cube container near the bottom of the inclined plane. Now

release the cylinder from the point A of the inclined plane. The cylinder strikes the plastic cube container which is at rest. The rolling cylinder moves the plastic cube container for some distance. Mark the place where the plastic container rests. Measure the distance between the original position and the new position of the plastic cube container. Repeat the experiment by releasing the cylinder from different heights (B.C.D) and measure the distance.

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Isthedistancemovedbythecontainersameinallthecases?Doesthecylinderstrikethecontainerwiththesamevelocity?

Whatisyourconclusion?Thekineticenergyofabodydependsonitsvelocity.Higherthevelocity,higheristhekineticenergy.

Repeatthesameexperimentusingalargesize(500g)cylindricaltintightlyfilledwithsand.

Comparetheresultwiththeaboveexperiment.Whatdoyouobserve?Whatisyourconclusion?Thekineticenergyofabodyalsodependsuponitsmass.Higherthemassofabody,higherisitskineticenergy.

Thekineticenergyofabodythereforedependson

1.themassofthebody.2.thevelocitywithwhichitismoving.

Abodyofmass‘m’movingwithavelocity‘v’hasthekineticenergyof

21 mv2.Youwillstudy thederivationof this formula in thehigherclasses.

Unit of energy:Energyismeasuredintermsofwork.Theunitofworkis‘joule’.Sotheunitofenergyisalsojoule.

Note : Changeinthekineticenergyofabodyisthemeasureoftheworkdone.

Example 1:Acarismovingwithuniformvelocityof15ms-1.Whatisthekineticenergyofaboyofmass40kgsittinginthecar?

solution:Velocityoftheboy=velocityofthecar

Kineticenergypossessedbytheboy=21 mv2Herem=40kg,v=15ms-1

=21 Í40kgÍ(15ms-1)2

=4500JExample 2 : Iftwobodiesofequalmassesmovewithuniformvelocityof‘v’and‘3v’,whatwillbetheratiooftheirkineticenergies?

Massoffirstbody = mVelocityofthefirstbody = vMassofsecondbody = mVelocityofsecondbody = 3v

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Theratioofkineticenergiesofthetwobodies=secKinetic energes of ond body

Kinetic energies of first body

( )m v

m v

mv

mv

21 3

21

2921

2

2

2

2

= =

91=

Theratioofthekineticenergies=1:9

Potential energyHowdoyoumakeatoydrumbeatertobeatthedrum?Youwindthe

springbeforeitbeatsthedrum.Yourworkdoneonthetoygetsstoredupinthespringintheformofenergy.Observetheshapeofthespringbeforeandafterthebeatsofthedrum.

Astoneislyingontheground.Itcannotdotheworkatthatmoment.Howdoyoumakethestonedowork?Liftthatstoneuptoyourshoulder.Nowtheworkhasbeendonebyliftingthisstoneagainsttheforceofgravity.Thisworkgetsstoredupinthestoneintheformofenergy.Nowthestonehasthecapacitytodowork.Herestonegetsenergyduetoitsposition.Theenergywhichabodypossesseseitherduetoitspositionorduetoitsdeformationiscalledpotential energy.Activity 10.4

Complete the table 10.2

Sl.No.

Object possessing potential energy

energy posessed by the object

due to position

energy possessed by the object due

to shape

1 The wound spring of a watch

2 A stretched rubber band

3 Mangoes in the tree

4 Water stored in the dam

5 Stretched bow

6 A car at the top of the hill

7 Pressed spring

8 Stretched sling of a catapult

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Relationship between mass, height and potential energy of a body

Whatarethe factorsonwhichpotentialenergydepends?Letusexplore!

Lift two shotputs separately of 1 kg and 3 kg eachup to yourshoulder.Inboththecasesworkdoneisstoredintheformofenergy.Inwhichshotput ismoreenergystored?What isyourconclusion?Potentialenergydependsuponthemassofthebody.

Fromtheground,liftashot-putweighing3kguptoyourshoulderlevel.Nowagain lift the sameshot-put from thegroundaboveyourhead.Inwhichpositiondoestheballacquiremaximumenergy?Whatisyourconclusion?Potentialenergydependsupontheheightthroughwhichitisraisedfromtheground.Hencepotentialenergyofabodydependsuponthemassofabodyandtheheighttowhichitisraisedfromtheground.Ifmisthemassofabodyraisedtoaheight‘h’thenitspotentialenergy ( ) .m g h here g Acceleration due to gravity# #= = Youcanstudythederivationofthisformulainhigherclasses.

Examples

1. Ifaccelerationduetogravityis10ms-2,whatisthepotential

energyofabodyofmass1kgkeptataheightof5m?

Potentialenergy ( 1 , 10 , 5 )m g h here m kg g m s h m2# #= = = =-

Potentialenergy=1kgÍ10ms-2Í5m

Potentialenergy=50J

2. Abagofwheatweighs200kg.Towhatheightshoulditberaisedsothatitspotentialenergyis9800joule(g=9.8ms-2)

Potentialenergy ( , . ,m g h here m kg g m s200 9 8 2# #= = = -

potentialenergy=9800joule)

2 .J Kg m s h9800 00 9 8 2# #= -

.

h200 9 89800

#=

h=5m

Thus,thebagofwheatshouldberaisedtoaheightof5m.

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Change of energy

Rub your palm together.Why does palm getwarm?Where didtheheatcome from?Herekineticenergyofyourpalmchanges intoheat energy. Switch on a fan.Which energymakes the fan rotate?Here electrical energy is changed intomechanical energy.Burn themagnesiumstrip.Whatdoyouobserve?Herethechemicalenergyischangedintoheatandlightenergy.Thechangeofenergyfromoneformtoanotherisknownastransformationofenergy.

Activity 10.5

Some activities in your everyday life are given below. Complete the table 10.3

Sl. SituationName the forms of energy beforetransformation

Name the forms of energy after transformation

1 Combustion of Petrol2 Combustion of L.P.G 3 Burning match stick 4 Running toy car5 Photosynthesis6 Falling rain drop 7 Flowing water from dam

Whenyouswitchonthebulb,apartofelectricalenergyisconvertedintolightenergyandsomepartofitisconvertedintoheatenergy.

Find out : To prepare a cup of tea of 100 ml.. joules of energy arerequired. To pumpbloodby anormalheart once.....joules of energy arerequired.

Energycanneitherbecreatednordestroyed.Itcanbeconvertedfromoneformtoanother.Thisisknownasthelawofconservationofenergy.

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Activity 10.6

Sun is the ultimate source of different forms of energy on the earth. Observe figure 10.2 and identify the energy transformation.

Fig10.2Energy

Rate of consumption of energy in relation to timeHave you seen the letter ‘W’ on thebulb?Betweena40Wand

60Wonbulbswhichbulbgivesmorelight?40W,60Wonbulbsindicatetheconsumptionofenergyingiventime.Here‘W’istheunitofpower.Therateofconsumptionofenergyisknownaspower.

,If W is the work done in time t then powertime takenwork done=

P

tw=

Theworkdoneismeasuredinjoulesandtimeinseconds.Sounitofpowerisjoules/second.Thisunitofpoweriscalledwatt.Whentherateofconsumptionishigherthenkilowattisused.

1kilowatt=1000W

1kW=1000W

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Problem

Abodydoes20joulesofworkin5seconds.Whatisitspower?

Powertime takenwork done

Powersj

Power W520

4

=

=

=

( ,

)sec

here work joules

time onds

20

5

=

=

Thus,thepowerofthisbodyis4watt. More activities for you

Activity 10.7

Fig.10.3

This model shows transformation of kinetic energy and potential energy. Take a mudguard and fix it on a wooden block and release the marble as shown in fig.10.3

Prepare a model as shown in the

Fig.10.4

figure 10.4. Wind the thread around the axis of the wheel. The wheel is raised and its potential energy increases. When the disc is released the wheel moves downwards. It acquires kinetic energy and loses potential energy. At the lowest position again it rises.

Activity 10.8

Record the changes that take place when a simple pendulum oscillates.

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Exercises :i. four alternatives are given to each of the following incomplete statement / question. Choose the right answer :

1. Thetypeofenergythatcanbeeasilyconvertedintootherformsis

a.sound b.light c.heatd.electricity

2. Kineticenergyispresentinthefollowing.

a.Waterstoredinadam b.Stretchedrubberband

c.Waterreleasedfromadam d.Compressedspring

3. TheCorrectformulatofindthevelocityofabodywithkineticenergy‘k’is

a.V=mk2 b.V=

mk2 c.V= m

k4 2

d.V= km21

4. The correct sequence of energy changes in hydroelectric powerstationis,

a.kinetictopotential,tomechanicaltoelectrical.

b.potentialtokinetictomechanicaltoelectrical.

c.potentialtoelectricaltomechanical.

d.potentialtoelectricaltokinetictomechanical.

5.Whichofthefollowingobjecthashigherpotentialenergy?

a.mass = 10kg g=9.8ms-2h=10m

b.mass = 5kg g=9.8ms-2h=12m

c.mass = 8kg g=9.8ms-2h=100m

d.mass = 6kg g=9.8ms-2h=20mii. fill in the blanks with suitable words

1. Unitofpoweris_____________.

2. Unitofenergyis_____________.

3. If a candle is burnt, the chemical energy is transformed into________________.

4. Thewaterstoredinanoverheadtankpossesses___________energy.

5. Inacinematheatreelectricalenergyistransformedinto____________and_______________energy.

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iii. Answer the following

1. State whether the energy possessed in the following is kineticorpotential;compressedspring,Stretchedbow,movingarrow,waterstoredinadam,astoneatthetopofabuilding,birdrestingonthebranchofatree,

2. Distinguishbetweenpotentialenergyandkineticenergyofabody.

3. Abusandacararemovingatthesamespeed.Whichofthetwohasagreaterkineticenergy?

4. A ball of mass 200 gram falls from a height of 5 metre?What is its kinetic energy when it just reaches the ground?(g=9.8ms-2)

5. There are a number of devices in common use that changeenergy fromone formtoanother.Namesomedevicesthatchange1. electrical energy into light energy 2. electrical energy intomechanicalenergy3.electricalenergyintoheat4.soundenergyintoelectricalenergy5.chemicalenergyintoelectricalenergy.

6. Describe themode of energy transformation in amechanical andquartzclock.

7. Whatkindofenergytransformationtakesplaceatthethermalpowerstation?

Same - Sightedness : Feel the presence of the Divine in all beings and treat them with the same standard as you treat yourself.

-Swami Vivekananda

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Chapter 11

CheMICaL reaCtIONS aND theIr tYpeSafter studying this chapter students :

• explainthemeaningofchemicalreactions.

• writeequationsoffamiliarchemicalreactions.

• namethereactantsandproductsofachemicalreaction.

• balancetheequationswhenunbalancedequationsaregiven.

• classifythegivenreactionsaccordingtotheirtypes.

• give illustrations from daily life for different types of chemicalreactions.

Chemical reactions and their types

Youmighthaveenjoyedeatingasweetmangooreatinganorange.Haveyouatanypointof time thoughtbeforeeating,howare theseproduced?

Byyourknowledgeyoumaysaythatitisbyphotosynthesis.Yes,photosynthesisisacomplexchemicalreactioncarriedoutbyplants.Itissocomplexthatitisdifficulttodescribeitindetail.

Therearemanychemicalreactionsthattakeplaceinourdaytodaylife.Asaresultofthesereactionsvarietyofsubstancesareformedbyninetynaturallyoccurringelements.

Know this : “Therearemore things inheavenandearthHoratio, thanaredreamtoffinyourphilosophy.”Thisphrase,takenfromShakespearedrama‘Hamlet’,describesthevarietyinnature.

Someofthereactionsthatweobservearecomplexandsomearesimple.Biogeochemical cycles that youhave studied in life sciencearecomplex.Rustingofiron,combustionoffuelsaresimplechemicalreactions.

Whatarechemicalreactions?Howaretheydifferentfromphysicalchangesorreactions?Youhavestudiedaboutphysicalchangesinyourearlierclasses,recallthem.

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Activity 11.1

Classify the following into chemical and physical changes.

1. Rusting of iron 2. Ripening of fruits 3. Magnetizing a steel plate

4. melting of iron 5. combustion of LPG 6. Cooling effect produced by ice

Chemicalchangesleadtotheformationofsubstancesthathelptogrowourfood,makeourlivesmoreproductiveandcomfortable,cureourdiseasesandmuchmore.

In chemical reactions electronsmay get transferred from oneatomtoanotherorsharedbetween twoatoms.Theelectrons in theoutermostorbittakepartinchemicalreactions.Sometimeselectronsin the penultimate orbitmay take part in chemical reactions alongwiththoseintheoutermostorbit.Theseelectronswhichtakepartinchemicalreactionsarecalledvalence eletrons,asyouhavestudiedinchapterIV.

Know this : All atoms like to get octet structure or completed shell ofelectrons. They try to acquire the electronic configuration of neareststable or noble gas. In this attempt atomsmay transfer, gain or shareelectrons.Maincauseofchemicalreactionisthedesireofatomstogetstableelectronic configuration. Rearrangement of the configuration may alsotakeplaceifthereareotherfavourablealternatives.

Chemical equations Consider the example of combustion of carbon in air. Carbon

combineswiththeoxygenoftheairtoformcarbondioxide.Canyouwritethisreaction?

Carbon+Oxygen→Carbondioxide

Thisis‘word’equation.Ithasqualitativemeaningonly.CarbonandOxygenarecalledreactants.Carbondioxideiscalledproduct.

Butthe‘word’equationconveysonlyoneinformationaboutreactantsandproducts.Ittellsus“what”?Butnot“howmuch”?Letuswritetheaboveequationusingformulaeandsymbols.

C+O2→CO2

Thisisthebettermethodofwritingthechemicalequation.Ithasthefollowingadvantage.

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• Qualitative:Helpsinknowingthereactantsandproducts.• Quantitative:Helpsinknowingtherelationbetweenthequanties

ofreactantsconsumedandproductsformedC:O2:CO2=1:1:1 Wecanfurtherimproveupontheequationbywritingtheother

conditions. C+O2

Heat CO2+energy

Remember : Thereactantsarewrittenonthelefthandside.Theproductsarewrittenontherighthandside.

SymbolsandMolecularformulaofreactantsorproductsshouldbeusedtowritetheequations.Consideronemoreexample.

Whenmagnesiumribbonisignitedinoxygen,itcatchesfirewithdazzlingwhitelightformingmagnesiumoxide.Magnesium+Oxygen→Magnesiumoxide(wordequation)(Qualitative)

2Mg+O2→2MgO(formulaequation)(Quantitative)2molesofMagnesium+onemoleofoxygen→2molesofMagnesiumoxide

WhycanwenotwritetheaboveequationasMg+O→MgO?Thisisnotthecorrectway.oxygengasconsistsofdiatomicmolecule.

Theratioofatomsinthemoleculesofreactantsshouldbeequaltotheratioofatomsinthemoleculesofproducts.

Mg+O2→MgOThisiscorrectmethodofwritingthereactantsandproducts

Know this : according to the law of conservation of mass or matter,‘matter canneither be creatednor destroyed’. Thenumber of atoms ofeachelementofreactantsonlefthandsideshouldbeequaltothenumberofatomsofeachelementpresentinproductsonrighthandside.

Thereisone‘Mg’onthelefthandsideandone‘Mg’ontherighthandside.Butthereisone‘O2’onlefthandsideandone‘O’onrighthandsidein‘MgO’.Wecannotwrite‘MgO’as‘MgO2’.AlsowecannotwritetheproductsasMgO+O.

Productsorreactantsshouldbemultipliedbyintegersinordertosatisfythelawofconservationofmatter.IfMgOismultipliedby2,itbecomes2MgO.NowtheOxygenatomsarebalanced.ButwehavetoincreaseoneMgby2MginordertobalancetheMagnesiumatoms.Thebalancedequationis2Mg+O2→2MgO

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Remember : In special cases we represent actual atomic state of anelement.Inthatcasesymboloftheelementiswritteninsquarebracket.

Eg:Hypochlorousacid Hydrochloricacid+NascentOxygen

HClO HCl+[O]

The practice of equalizing the number of atoms of elements onlefthandsidetothecorrespondingatomsonrighthandsideiscalledbalancing of equations.

Consideronemoreexample:H2+O2→H2OInthisexampleequalnumberofhydrogenatomsarethereoneither

sidebutnumberofoxygenatomsareunequal.H2+O2→2H2OThe hydrogen atoms on right hand side are four.Multiply the

hydrogenmoleculeonlefthandsidebytwotobalancethehydrogenatoms.Thebalancedequationnowwillbe

2H2+O2→2H2OActivity 11.2

Balance the following

• Al + Cl2 → AlCl3 [clue: multiply AlCl3 by 2]

• KClO3 → KCl +O2 [clue: multiply KClO3 by 2]

• Pb3O4 → PbO +O2 [clue : multiply Pb3O4 by 2]

• Zn + HCl → ZnCl2 + H2

Thereisnoparticularmethodofbalancingequations.Itshouldbelearntbytrialanderrormethod.Youwillgetusedtoitwhenyoupractisewritingofequationsintheotherlessonsofthistextbook.

types Of Chemical reactionsThechemicalreactionsaremainlyoffollowingtypesbasedonthe

natureofreactantsandproducts.• Chemicalcombination• Chemicaldecomposition• Chemicaldisplacement• Chemicaldoubledecompositionorexchange

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1. Chemical combination

Activity 11.3:

When sulphur is ignited in air on a metal spoon, it buns with pale blue flame, producing sulphur dioxide gas.

S + O2 → SO2

This is combination between two elements.

Activity 11.4:

Bring a glass rod dipped in liquor ammonia near the opened stopper of con-centrated hydrochloric acid. We get dense white fumes of ammonium chloride.

NH3 + HCl → NH4Cl

In this reaction two compounds react to form another compound.

Chemicalcombinationisareactioninwhichtwoormoreelementsorcompoundscombineto formanewproduct.ThisprocesshasanindustrialapplicationnamelysynthesisofammoniabyHaber’sprocess.

N2+3H2→2NH3

(InChemicalcombinationmanyreactantscombinetoformsingleproduct)

Know this : haber’s process: Ammoniagasisarawmaterialformanufacturingfertilizers.Haberdesignedatechnologyofsynthesizingammonia.HewonNobelprize inChemistry for this contribution. In thisprocessNitrogenandHydrogenaresubjectedtohighpressureatatemperatureofabout500ºCinthepresenceofacatalyst.

Activity 11.5

During lightening Nitrogen and Oxygen of the atmosphere combine. Can you list the reactants and products? Write the balanced equation of the reaction.

2. Chemical decomposition

Heatabout5gofpotassiumpermanganateinatesttubeforsometime.Bringaglowingincensesticknearthemouthofthetesttube.Theglowingsplintercatchesfire.ItisbecauseoftheliberationofOxygen.

2KMnO4→K2MnO4+MnO2+O2

Potassiumpermangnate→pot.manganate+manganesedioxide+oxygen.

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TheclassicexperimentofJosephPriestlywhopreparedOxygenbyheatingmercuricoxideinatesttubebyconvergingsunraysusingaconvexlens,isshowninthefigure.

2HgO→2Hg+O2

Inchemicaldecompositionacompoundbreaksupintotwoormorenewsubstances.Normallyenergyhastobeprovidedforthispurpose.

fig11.1Preparationofoxygenbyheatingmercuricoxide

Recall : Whenelectriccurrent ispassed throughacidifiedwater,waterbreaks up into hydrogen and oxygen. Water was considered as singleelement.Fromthisexperimentitcanbeshownthatitisacompound.

InChemicaldecompositionasinglereactantgivesmanyproducts.

3. Chemical displacement

Activity 11.6

Immerse an iron nail in copper sulphate solution for some time. You will observe the deposit of copper on iron nail.

CuSO4 + Fe → FeSO4 + Cu

Note : Coppersulphateispoisonous.

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Activity 11.7

Take Clear bleaching powder solution in a test tube. Add potassium iodide solution. We get a violet coloured Iodine.

Cl2+2KI→2KCl+I2

Intheabovetwoexamplesmorereactivemetalornonmetaldisplaceslessreactivemetalornonmetalrespectively,fromtheircompounds.These are the examples of displacement reaction.Can you arrangeCopper,IronandSilverintheincreasingorderofthereactivity?

Activity 11.8

Observe the following reaction:

Zn + H2SO4 → ZnSO4 + H2 (dilute)

Identify the displaced element and displacing agent in the above reaction.

Inchemicaldisplacementmorereactiveelementdisplacesthelessreactiveelementfromtheircompounds.

Findout : Thoughbydisplacementreactionwecandepositsilveronironorcopper,itisnotusedasamethodofcoating.Forcoatingsilveronor-namentselectroplatingisused.

4. Chemical double decomposition or chemical exchange or chemical double displacement

Activity 11.9

Add sodium carbonate solution to magnesium sulphate solution, in a test tube. We see white precipitate.

MgSO4 + Na2CO3 → MgCO3 + Na2SO4

Activity 11.10

In a test tube add sodium carbonate solution to calcium chloride solution.We see a white precipitate.

CaCl2 + Na2CO3 → CaCO3 + 2NaCl

In the above two examples there is mutual exchange of metallic and the non metallic parts. Such reactions are called double displacement or double decomposition reactions.

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Activity 11.11

In the following example can you write the parts or radicals which are exhanged?

MgCl2 + Na2CO3 → MgCO3 + 2 NaCl

Oxidation and reduction:You know that iron commonly occurs as oxide along with

impurities. One such common oxide of iron is Ferric Oxide(Fe2O3). If Oxygen is removed from this using Carbon we getiron. Substances which remove Oxygen from a compound arecommonly called reducing agents. They easily give up oxygen.Thereducingagentitselfgetsoxidized.TheoldmeaningofoxidationisadditionofOxygen.SimilarlytheoldmeaningofreductionisremovalofOxygen. This concept hasundergonemany changes. In terms ofelectronic theory, oxidation is aprocessof transferringof electrons.Reductionisaprocessofreceivingofelectrons.

Potassiumpermanganate,Potassiumchlorate,PotassiumnitrateandHydrogen peroxide are some commonly used oxidizing agents.Theyeasilygiveupoxygen.Carbon,Magnesium,HydrogensulphideandSulphurdioxidearesomecommonlyusedreducingagents.Theyeasilytakeupoxygen.

exercises :

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Balancingofequationsisbasedon,

a.avogadro’snumber

b.principleofconservationofmomentum

c.conditionsforachemicalreactiontotakeplace

d.lawofconservationofmassormatter

2. Identifythebalancedequationinthefollowing.

a.SiO2+Mg→Si+MgO

b.SiO2+2Mg→Si+2MgO

c.SiO+Mg→Si+MgO2

d.SiO2+Mg→SiO+2MgO

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3. Correctstatementaboutchemicaldisplacementis,

a.lessreactiveelementdisplacesmorereactiveelement

b.anon-metaldisplacesmorereactivenonmetal

c.morereactiveelementdisplaceslessreactiveelement

d.evolutionofheatwhencarbonisburntinair

4. Dissolvingofsugarinwaterisnotanexampleforchemicalreactionbecause,

a.thereisnochangeinenergy

b.sufficientheatisnotproduced

c.nonewsubstancesareformed

d.nogasesareevolved

5. Whichofthefollowingrepresentscombinationoftwocompoundsforminganothercompound?

a.2SO2+O2--→2SO3

b.CaCO3→CaO+CO2

c.H2O+SO2→H2SO3

d.2Na+2H2O→2NaOH+H2

II. Fill in the Blanks with suitable words :

1. Chemicalequationshavebothqualitativeand_________significance

2. Zn+2HCl-→ZnCl2+________________.

3. 2Mg+O2-→2MgOInthethisreactionthereactantsare_______and________________.

4. CopperSulphate+Iron-→IronSulphate+________________.

5. 2Al+3Cl2-→________________.

III. Balance the following reactions :

1. Cu+H2SO4-→CuSO4+SO2+H2O

2. Fe+H2O-→Fe3O4+H2

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IV. Match the Following

A B

1.chemicalcombination a.Fe+H2SO4→FeSO4+H2

2.chemicaldecomposition b.FeS+2O2→FeSO4

3.chemicaldisplacement c.AgNO3+NaCl→AgCl+NaNO3

4.chemicaldoubledisplacement d.2Pb3O4→6PbO+O2

V. answer the following

1. Classify the following into chemical combination, decomposition,displacementanddoubledisplacementreaction.

a.CaCO3→CaO+CO2 b.2AgNO3+Cu→Cu(NO3)2+2Ag

c.2SO2+O2→2SO3 d.NaCl+AgNO3→AgCl+NaNO3

2. State the advantages of writing a chemical equation usingformulaeandsymbols.

3. Mentiononeexampleeachforthedifferenttypesofchemicalreac-tions.

4. In chemical equations if Oxygen or Chlorine is one of thereactantstheyarerepresentedas‘O2’and‘Cl2’butnotas‘O’or‘Cl’.Why?

5. Duringwintermanyplant leaves fall on the earth.But itwillnotcausepollution.Plasticpaperswhicharestrewnontheearthcausepollution.Namethetypeofchemicalreactionassociatedwiththisobservation.

6. L.P.Ggascontainsbutane.ItsmolecularformulaisC4H10.Namethepossibleproductswhenitundergoescompletecombustion.

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CHAPTER 12

CHEMICALS IN OUR DAILY LIFE-1After studying this chapter students :

• listthephysicalandchemicalpropertiesofchlorine,sulphurdioxideandbakingsoda.

• namecommoncompoundscontainingchlorineandsulphur.

• draw neat diagrams showing experimental set up of laboratorypreparationofchlorineandsulphurdioxide.

• listtheusesofchlorinecompounds,sulphurdioxide,bakingsodainourdailylife.

• explainthemethodsofmanufacturingsulphurdioxide,bakingsoda.

• compare the bleaching action of sulphur dioxide with that ofchlorine.

• explainthemethodsofmanufacturingofsoapsanddetergents.

• statethedifferencesbetweensoapanddetergent.

• listouttheadvantagesanddisadvantageofdetergents.

Chlorine Preparation, Properties and Uses

Commonsaltisoneofthechemicalsubstanceswhichgivestastetoourfood.Whatisthechemicalnameofcommonsalt?Haveyouseenthebleachingpowder?Canyourecognizebleachingpowderusedatyourhomebythepungentsmell,whenitisbeingused?Whichisthecommonelementpresentinbleachingpowderandcommonsalt?Thecommonelementischlorine.Letuslearnmoreaboutchlorine.

Minerals of Cholrine : Haliteorrocksalt,sylvite,camallite,chlorapatitearethemostcommonmineralsofchlorine.

ChlorineoccurscommonlybothintheEarth’scrustandinseawater.

Find out : AnatomofChlorinehas17electrons.Findoutthenumberofprotonspresentinanatomofchlorine.

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Activity 12.1

When you purchase medicines,read the constituents of medicine on its wrapper and list out the chlorine compounds used for the preparation of medicine.

Chlorineisusedforvariouspurposes.Nowletuslearnabouttheprocessofmanufactureofchlorineonlargescale.

In industry,chlorine isproducedbypassinganelectriccurrentthrough an aqueous solution of sodium chloride or throughmoltensodiumchloride.Theproductsproducedalongwithchlorinearesodiumhydroxide(NaOH)andhydrogen(H2),duringtheelectrolysisofaqueoussodiumchloridesolution.

Know this : Solutionsmadeusingwaterarecalledaqueoussolutions.Thesolid stateofmatterbecomes liquidwhensufficientlyheated.The liquidstateofmatteriscalledmoltenstate.Insolublesubstancethatisformedinareactioniscalledprecipitate.

CarlWilhelmScheele

Carl Wilhelm Scheele

In1774,SwedishchemistCarlWilhelmScheeletriedthereactionofhydrochloricacidonmanganesedioxide.Heobserveda greenish gas. He thought that theliberated gas was oxygen. But it wasnot oxygen ashe thought.Until 1810,nobodyknewthatthe libratedgaswaschlorine.Butin1810SirHumphreyDavyidentifiedthegasasadistinctchemicalelement, andnamed it “chlorine”. Thename chlorine is originated from theGreek word ‘chloro’. Chloromeaning‘pale green’.

We can also prepare chlorine in a small quantity in laboratory. Method 1

Setuptheapparatusasshowninfigure12.1.Takenearly20gofmanganesedioxideintheflask.Addconcentratedhydrochloricacidtoitthroughthistlefunnelsothattipofthethistlefunnelisdippedintheacid.Heattheflask.

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Fig12.1PreparationofChlorine

Nowobservethecolouroftheliberatedgasintheflask.Thisgasiscollectedinthejarbytheupwarddisplacementofair.

MnO2+4HCl→MnCl2+Cl2 +2H2O

Method 2

Fig12.2PreparationofChlorine

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Whenconcentratedhydrochloricacidisaddeddropbydroptosolidpotassiumpermanganate,chlorinegasisliberated.Theliberatedgasiscollectedinseparatebottlesbytheupwarddisplacementofair.

Theapparatusissetupasshowninfigure12.2.

Think : The liberated gas is collected using gas jar by the upwarddisplacementofair.Why?Thistlefunnelshouldbedippedintheacidwhy?Theliberatedgasispassedthroughthewater.why?Thechlorinegaspassedthroughthewoulfeebottlecontainingconcentratedsulphuricacidwhy?

Know this : One can get chlorine gas by using vinegar and bleachingpowder.

CollectchlorineinfivejarsandconductthefollowingActivity

Activity 12.2

Experiment Observation Inference

Introduce a burning candle into a jar of chlorine gas

burns with dull flame and sooty flame

supporter of combustion(but not like oxygen)

Introduce a few rose petals soaked in water in a jar of chlorine.

decolourisation bleaching property

Introduce rose petal into another jar of chlorine without soaking in water

colour does not disapper quickly.

In the abscence of water bleaching action will not take place.

Hold wet blue litmus separately in chlorine jar.

blue litmus becomes red

acidic property

Collect chlorine in a jar pale greenish yellow

chlorine gas has colour.

Onthebasisoftheaboveactivitieslistthephysicalpropertiesofchlorine.

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Chemical properties

Letuslearnchemicalpropertiesofchlorine.

1. Introduceaburningmagnesiumribbonintoajarofchlorinewiththehelpofapairoftongs.Whatdoyouobserve?Whatisthecolourofmagnesiumchloride?Writethechemicalequation.

Mg+Cl2→MgCl22. Chlorine reacts with hot red phosphorus giving phosphorus

pentachloride 2P+3Cl2→2PCl3 [limitedsupplyofchlorine]

2P+5Cl2→2PCl5 [excesssupplyofchlorine]

3. IntroduceasmallpieceofdrysodiumintoajarcontainingChlorine.Whatdoyouobserve?Nametheproductformedinthejar.Writethechemicalequation.Sodiumburnsvigorouslywithgoldenyellowflame.

[Caution:Conductthisexperimentcarefully]

2Na+Cl2→2NaCl4. Sprinkleheatedaluminumpowderintoajarofchlorine.Whatdo

youobserve?Nametheproductformedinthejar.Writethechemicalequation.

2Al+3Cl2→2AlCl3Aluminumparticlesburnwithbrightflashesoflight.

5. When chlorine gas is dissolved in water hypochlorous acid isformed.ThisHypochlorousacidreleasesnascentOxygen[O]andbecomeshydrochloricacid.NascentOxygenisapowerfuloxidisingagentwhichisresponsibleforbleachingandsterilizingpropertyofchlorine.

Historical use of Chlorine : Chlorinewasfirstused in thesterilisationofdrinkingwaterinthe19thcenturytocontrolthespreadofwater-borndiseases suchas typhoid, cholera, dysentery and gastro-enteritis,whichkilledpeoplemorethanthepeoplewhowerekilledinallwarsinhistory.

Know this : Inadditiontosterilisationofwater,chlorinecontrolsthegrowthofslimeandalgaeinmainpipesandstoragetanks,andhelpstoremoveunwantednitrogencompoundsfromwater.

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Find out : Collect informationabout themethodof sterilizationwithoutusingchemicals.

Note : Use of excess of chlorine should be avoided in the treatment ofpotablewater.

Uses 1. Chlorineisusedinthemanufactureofbleachingpowder.2. Chlorineisusedinthemanufactureofhydrochloricacid.3. Itisusedinpaperandpulpindustry.4. Fordomesticpurpose,itisusedasbleachingagentandinpurification

ofwater.

5. It is used in themanufacture of Polyvinylchloride (P.V.C) andchlorofluorocarbons(C.F.C.)

6. Chlorine is used in the preparation of pesticides likebenzene hexachloride commonly calledBHC, dichloro diphenyltrichloroethane(D.D.T).

7. Medicalapplications

• Common salt is the basic component of intravenous salinesolutions.

• Itisusedinthepreparationofchloroformwhichisusedasananaesthetic

Think : Overuse of bleaching powder should be avoided in toilet pitsystem.Why?

Know this : Whenchlorinegasispassedintoslakedlimeat4000C,bleachingpowderisformed.

Ca(OH)2+Cl2 CaOCl2+H2O

(calciumoxychloride)

Know this : Bleachingistheprocessofwhiteningorremovingthenaturalcolourof textilefibre, yarnsand fabrics,organic substanceandofwoodpulpbytreatmentwithchemicals.

Know this : C.F.C.usedinrefrigerator,isharmful.Whyisitharmful?Collectinformation.

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Know this : D.D.T.wasfirstpreparedin1873,butwasnotusedasapes-ticideuntilWorldWarII.(1939-45)

Public health officials were at first delighted to learn that D.D.T. killsdisease-carryinginsectsveryefficientlyandtheyfounditcouldkillmanyofthepeststhatattackedcrops.Bytheendofthe1950s,manyfarmersweresprayinghugeamountofD.D.T.ontheirlandtogetridofpests.

TheadverseeffectofD.D.T.onhumanhealthisnowscientificallyestablished.(Fordetailsreferchapter2).

Sulphur dioxide: preparation, properties and uses

Eggyolk,cauliflower,raddish,onionandgarliccontainsulphur.Ourhair,nailsandskinalsocontainsulphur.Whentheyareburntyougetapeculiarsmell.Thepeculiarsmellisduetothepresenceofsulphurdioxide.Letuslearnmoreaboutsulphurdioxide,acompoundofsulphur.

Know this : During the extraction of copper and mercury fromcopper pyrites and cinnabar respectively, sulphur dioxide is released.In the purification of petroleum, sulphur dioxide is released. Sulphurdioxideisreleasedfromcoalinpowerplantandduringvolcanicerruption.

Discovery of Sulphur Dioxide: Priestleypreparedsulphurdioxideintheyear1774byheatingconcentratedsulphuricacidwithmercuryandcalledit“Vitriolicacidair”.ButitwasLavoisier,whoprovedthatitwasanoxideofsulphur.

Let us learn themethods by which sulphur dioxide can bemanufacturedonlarge-scale.

1. Sulphur is present inmanyminerals. One of theminerals ismercuroussulphide.Itiscommonlycalledcinnabar.Thesulphideoreburnsinthepresenceofairandsulphurdioxideisobtainedasbyproduct.

HgS+O2→Hg+SO2

2. Duringtheextractionofzincfromzincblende.Sulphurdioxideisobtainedasbyproduct.

2ZnS + 3O2 → 2ZnO + 2SO2

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3. Letusstudythelaboratorymethodofpreparationofsulphurdioxideandstudysomeoftheproperties.Setuptheapparatusasshowninfigure12.3.Copperturningsandconcentratedsulphuricareusedinthepreparationsalphurdioxide.

Theheatingofconcentratedsulphuricacidwithcopperturningsyieldcoppersulphate,sulphurdioxideandwater.

Cu+2H2SO4→CuSO4+SO2+2H2O

Observefigure12.3;describethearrangementoftheapparatusinyourownwords.

Fig12.3PreparationofSulphurdioxide

Youcanalsopreparesulphurdioxidewiththehelpofyourteacherbyusingsodiumsulphatecrystalsanddilutehydrochloricacidordilutesulphuricacidbyusingsameapparatussetupasgivenabove.Thechemicalequationisgivenbelow.

Sodiumsulphate+dil.Hydrochloricacid Sodiumchloride+Water +Sulphurdioxide

Collectsulphurdioxideintwojarsandconductthefollowingtests

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Activity 12.3

Experiment Observations Inference

Introduce a burning candle into a jar of sulphur dioxide gas

Flame is extinguished.

Not a supporter of combustion

Pass sulphur dioxide for about five minutes into a 400 ml beaker half filled with water. Dip wet blue litmus.

Blue litmus turns red.

Solution is acidic.

Based on the above observations, list the properties of sulphurdioxide.Inadditiontothis,notethatsulphurdioxideiscolourlessandhasapungentsmell.Donotsmellthegasdirectly.

Activity 12.4

Heat sulphur in a spoon. Hold wet and blue litmus paper separately on the liberated gas. What do you observe?

Now let us study about the action of sulphur dioxide onwater,moistureandmagnesium.

1Sulphurdioxidereactswithwatertogivesulphurousacid.

SO2+H2O→H2SO3

Acid rain: Water molecules in the atmosphere react with sulphurdioxidetoformacidrain.Thisacidraincorrodesmonuments,statuesandbuildings.Itaffectstheoffertilitythesoilandaffectsplantgrowth.Incertainindustrialregions,theatmospherecontainssulphurdioxidealso.

Find out : Whatisthedifferencebetweensulphuricacidandsulphurousacid?

Collectsulphurdioxideinthreejarsandconductactivity12.5tostudythepropertiesofsulphurdioxide.

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Activity 12.5

Experiment Observation Inference1. Introduce a few petals of rose flowers soaked in water in a jar of sulphur dioxide.

1. Decolourisation takes place.

2. Acts as bleaching agent.

2. Take out the petal from the jar and expose it to air.

1.Colour is regained. 2. Bleaching action is temporary.

3. Introduce a few petals of rose flowers in to another jar of sulphur dioxide without soaking in water.

1. No change. 2. Dry sulphur dioxide is not a bleaching agent.

1. Sulphurdioxidebleachesbyreductionprocess.Itistemporary.

2. Keepaburningmagnesiumribboninsidethesulphurdioxidejar.Whatdoyouobserve?

Magnesiumcontinuestoburndisplacingsulphurparticleswhichsticktothejar.

2Mg+SO2→2MgO+S

Think: Sulphurdioxidedoesnotburnandalsodoesnothelpinburning.Thenhowdoesmagnesiumburn?

Uses of sulphur dioxide1. Sulphurdioxideisusedinthemanufactureofsulphuricacid,which

istherawmaterialforthemanufactureofdetergents,fertilizersandmanymedicines.

2. Itpreventsthegrowthofbacteriaandfungus;henceitisusedtoincreasetheshelflifeoffoods.

3. InsugarindustrySulphurdioxideisusedtoremovecolouringmatterfromsugar.

4. Itisusedtopreventdecolourisationofdriedfruits.

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Know this : Sulphurdioxide isoxidized tosulphur trioxideand treatedwith water to form sulphuric acid. Commonly used fertlizer ammoniumsulphateisobtainedbytheactionofsulphuricacidonammoniagas.

Sulphuric acid is one of the important industrial products thatdeterminestheprosperityofacountry.

Sodium bicarbonate (Baking soda)

Youmighthaveheardaboutusingsodiumbicarbonatewhilecookingsome food items.What is the scientificbackgroundofusingbakingsoda in preparing different types of food items? Let us learn aboutmanufactureofbakingsodaonlargescale

Activity 12.6

• Place a bottle on the table and remove the lid. Carefully pour 2 tablespoons of vinegar into the bottle.

• Put 1 teaspoon of baking soda into the balloon using a separate spoon.

• Without spilling baking soda, stretch the mouth of the balloon over the mouth of the bottle.

• Turn the balloon completely upright so that baking soda inside the balloon pours into the bottle on the vinegar. Watch!

• What happens inside the bottle?

• What happens to the balloon? Why?

Activity 12.7

Prepare solutions of the following substances:

washing soda, calcium hydroxide, lemon juice bleaching powder vinegar, detergent, baking soda, and Soda water.

Put a drop of each of the above solutions on a watch-glass and test by dipping red and blue litmus paper in it.

What happens? Why?

Baking soda is manufactured by passing carbon dioxide through saturated sodium carbonate solution in water.

Na2CO3 + CO2 + H2O → 2NaHCO3

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Activities 12.8

• Take a spoon of baking soda. Observe its colour and physical state

• Put blue and red litmus into the solution of baking soda. What happens? What do you understand?

• Take aqueous sodium bicarbonate in a test tube and heat it. The evolved gas is passed through lime water. What do you observe? which is the gas liberated?

• Squeeze a piece of lemon on sodium bicarbonate in a test tube. What happens? Pass the gas through lime water. What happens?

Based on the above activities list out some properties of baking soda.

Uses of baking soda• Bakingsodaisthecomponentofbakingpowderusedinbakeryto

makethebakeryitems.• Sodiumbicarbonateisusedinmedicinewhichactsasantacid,to

treatexcessofacidformedinthestomach.• Itisusedasamildcleaningagent.• Itisusedtoprepareaeratedwater(sodawater)

Soaps and detergentsWearefamiliarwiththeuseofsoapinourdailylife.Cleanliness

isoneof thegoodhygienicpractices.Youare familiarwithdifferenttypesofcleaningmaterialslikeshampoo,shavingsoap,washingsoap,toiletsoap.Acleaningsubstancemadefromanimalfatsorvegetableoiliscalledsoap.Acleaningsubstancewhichismadeusingpetroleumis calleddetergent.Wash the clothes inhardwaterusing soapanddetergent.Whatdifferencedoyoufind?Soapdoesnotgivelatherwithhardwatereasilywhy?Therearedifferentformsofsoapsavailableinthemarket.Nowletusdiscussthemanufactureofsoap,detergentandliquidsoapindetail.

Why are detergents called soapless soaps?

Detergentactslikeasoapinthecleansingproperties,theydonotcontaintheusualsoapslikesodiumstearate.

Thekettlemethodofmakingsoapisstillusedtodayonasmallscaleincottatgeindustries.Therawmaterialsusedareoil,sodiumhydroxideorpotassiumhydroxideandcommonsalt.

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The mixture of fats and sodium hydroxide are allowed to boil in the kettle using the steam coil within the kettle. After boiling, the mass thickens as the fat reacts with the sodium hydroxide producing soap and glycerine. Salt is added to separate soap from glycerine. The soap forms its layer at the top and the glycerine settles at the bottom. The glycerine is taken out from the bottom of the kettle. Soap is taken off from the top. The soap is then cooled.

Oil/fat + sodium hydroxide → soap + glycerol

Know this : glycerol or glycerine is a sweet viscous liquid soluble in water. It is used in the manufacture of explosives, plastics and pharmaceuticals.

Activity 12.9

Are you interested in preparing soap? Take 30 ml of vegetable oil in a beaker. Dissolve 20 grams of sodium hydroxide in 100 ml of water in another beaker. Take 60 ml of this solution and add this to 30ml of oil. Heat the mixture slowly until the mixture boils. After 15-20 minutes of boiling, add about 5 grams of sodium chloride to the mixture. Stir well. What do you observe? Take soap out of the beaker and spread it on a tray and allow it to dry. Now soap is ready to wash.

During the World War I, Germany developed detergents in response to the shortage of fats for making soaps. Let us consider a method of manufacturing detergents. Long chain hydrocarbons obtained from petroleum are treated with concentrated sulphuric acid. Then it is neutralized with sodium hydroxide. The sodium salt thus obtained is detergent.

Think : Overuse of synthetic detergents cause water pollution. Why?

Now-a-days we use liquid soap in our daily life. Let us consider a method of manufacturing liquid soap. Heat the mixture of oil and potassium hydroxide solution. . Stir well. As the soap cooks, it will be converted to gel phase. Add distilled water and stir well. Add little scent. Liquid soap is ready.

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Exercises :

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1.Chlorineispreparedinthelaboratorybytheactionof,

a.ZnandHCl b.MnO2andHCl

c.CaCO3andHCl d.Pb(NO3)2andHCl

2.Thechiefsourcesofoilsusedtomakesoapare,

a.petroleumproducts b.coalandcoke

c.animalsandplants d.soapsanddetergent

II. Fill in the blanks:1.MnO2+HCl→MnCl2+___________+____________.

2.Commonnameofsodiumchlorideis___________________.

3.Chemicalnameofbakingsodais___________________.

III. Answer the following :1. Pureanddrychlorinegasiscollectedbytheupwarddisplacementof

air.Givereason.

2. Namethecompoundofchlorine1.whichisananaesthetic2.whichisusedasarefrigerant3.whichisadisinfectant4.whichisusedtomakepipesandtubes5.whichliberateschlorineonexposuretoair.

3. Mentionfourusesofchlorine.

4. Namethemetalandtheacidtobeselectedtopreparesulphurdioxideinthelaboratory.

5.Nametheacidformedwhensulphurdioxidedissolvesinwater.

6. Givetwousesofsulphurdioxide.

7. Mentionanytwodifferencesbetweensoapandsyntheticdetergent

8. Howisdetergentindustriallymanufactured?

9. Whyisdetergentbetterthansoapincleaningaction?

Project Work : Visit a water treatment plant and collect information about

purificationofwater.

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CHAPTER 13

CHEMICALS IN OUR DAILY LIFE - II After studying this chapter students :

• recallbiologicalsignificanceofwater.

• conductexperimentstoknowtheactionofmetalsandnonmetalsonwater.

• writethechemicalformulaeandbalancethegivenequations.

• arrangethegivenmetalsintheorderofreactivitywithwater.

• statethechemicalpropertiesofwater.

• classifythegivensubstancesintodeliquescentandefflorescentsubstances.

• identifythehardnessofwaterthroughexperiment.

• explainthemethodsofremovalofhardnessofwater.

Youknowthat,waterisoneofthemostabundantandimportantcompounds in the world. It is themajor constituent of all livingorganisms.Someplantscontainmorepercentageofwater.Thehumanbodyhasabout65%ofwater.Neitherplants,animalsnorhumanbeingscansurvivewithoutwater.

Recall : Thebiologicalsignificanceofwater.Holywater,Ab-e-zam-zam,Gangajalaretraditionallyusedwordsinourculture.Riversarerespected.Thesethingshaveinherentbiologicalsignificanceofwateranddepictwaterasapreciouscommodity.

Waterismadeupofelementshydrogenandoxygen.Onemoleculeofwatercontainstwoatomsofhydrogenandoneatomofoxygenwhicharechemicallycombined.

Fromtimeimmemorial,waterhasbeenthedrivingforceofeverycivilizationandpeopleattachedgreatimportancetoanadequatesupplyofwater for different, purposes like agriculture, cooking, drinking,washing.

Inayurvedawaterhasbeengivenanimportantplace.WateralsoisusedtoTreatcommonhealthproblems.ItiscalledHydrotherapy.

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Purification of water :

Do you know ? Traditionalmethodsofobtainingpotablewaterincludethefollowing.boil-ing,makingsunlightfallonthewater,addingTulasileaves,camphor,drop-pingredhotironballs.

Therearemethods for removalof colour,odour, suspendedmatterandmicrobesfromthewater.Aslotherearemethodsofremovalofhardness.Water treatments include stages of coagulation or sedimentation,filtraton, decolourisation, deodourization and sterilisation. Alum is usedfor sedimentation. Some of these practices have been used in ancientcivilizationalso.

Whyisceramicfiltercandleusedinwaterpurificationequipment?

Waterisaverygoodfireextinguisher.Thoughitcontainscombustiblehydrogen and supporter of combustion oxygenwater is neither asupporterofcombustionnoracombustiblesubstance.

Find out : Whydoeshydrogenloseitscombustibilityafteritcombineswithoxygen?Whydoesoxygenloseitsabilitytosupportburning?

Waterisacompoundandbehaveslikeasinglesubstance.

Theburningofhydrogenisthereactionofcombustionofhydrogenwithoxygen.

Know this : Fishlivinginwaterabsorbdissolvedoxygenforrespiration,notoxygenfromthecompound‘water’.

Youhavestudiedphysicalpropertiesofwaterinthepreviousclasses.Nowletuslearnmoreaboutthechemicalpropertiesofwater.

Chemical Properties Of Water

Fig.13.1Structureofwatermolecule

YouknowthatchemicalformulaofwaterisH2O. Inawatermoleculeoneatomofoxygenisboundtotwoatomsofhydrogen.asshowninfigure13.1.

Wateriscalledthe“universal solvent”becauseitdissolvesmoresubstancesthananyothersolvents.

Find Out : Seawaterissalty.Why?

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Activity : 13.1

Dip a piece of blue or red litmus paper in pure water. What inference do you draw from this activity?

Action of water on metalsWestorewaterindifferentmetalliccontainers.Wealsoboilwater

inmetalliccontainers.Doeswaterreactwiththemetalliccontainer?

Metalslikecopper,aluminiumandtinshownoactionwithwateratordinarytemperature.

Manymetalsandtheiralloysareusedtoprepareutensils,buckets,kitchenwareandotherarticles,becausetheydonotreactwithwaterundernormalconditions.

Sodiumandpotassiumaresoftmetalsandcanbecutwithaknife.They reactwithwater, forming their respective hydroxide liberatinghydrogengas.

Metalslikepotassiumandsodiumarekeptinkerosene.Why?Activity 13.2:

Take a clean piece of sodium. Dry it using blotting paper. Cut a small piece of it about the size of a green gram dhal. Drop it in water kept in a beaker carefully. Notice that the sodium piece rushes here and there reacting with water violently. It gradually diminishes in size and finally disappears. It reacts with water forming sodium hydroxide and hydrogen .Test the

resulting liquid in the beaker with blue and red litmus papers. The solution is basic.

Note : Sodiumistobekeptunderkeroseneasitcanreactwithoxygenandwater vapourspresent inair.Themetal shouldalwaysbehandledwithapairoftongsbecauseitcanevenreactwithmoistureonthehandandcauseblisters.Kerosenehasnoaffinitytowardssodium.

Metals like sodium potassium react with cold water formingrespectivehydroxidesliberatinghydrogengas.

2Na +2H2O→2NaOH+H2

Fig.13.2

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Activity : 13.3

Write the equation for the reaction between potassium and water.

Recall : Metals like Iron formrust.Theprocessof rustingwillbequickduring rainy season. Rust is hydrated oxide of iron. How can this beprevented?

Othermetalsalsoreactwithwateratdifferentconditions. Ca+2H2O→Ca(OH)2+H2 (Roomtemperature) Mg+2H2O→Mg(OH)2+H2(boilingwater)

Whensteamispassedoverredhotmetalslikezinc,iron,magnesiumwegetrespectiveoxidesandhydrogengas.

Zn+H2O → ZnO+H2 3Fe+4H2O→ Fe3O4+4H2 Mg+H2O → MgO+H2

Action of steam on non-metals:

1.Whensteamispassedoverredhotcoke,Mixtureofcarbonmonoxideandhydrogenisformed.

C+H2O→ CO+H2

Mixture of carbon monoxide and hydrogen in the ration of 1:2 is called water gas. Uses of water gas:

. asanindustrialfuel.

. usedinthemanufactureofhydrogen(Boschprocess)

2.Whensteamispassedoverredhotsilicon,whichisanonmetal,silicondioxideandhydrogengasareformed.

Si+2H2O→ SiO2+2H2

Reaction of water with non metallic oxides:

Generallywhenanonmetallicoxidedissolvesinwater,acidisformed.

CO2+H2O→ H2CO3(Carbonicacid)

Carbonicacidispresentinsoftdrinks.

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Acid rain

When nitrogen dioxide, and sulphur dioxide present in theatmosphereofcertainindustrialregions,dissolveinrainwater,theycauseacidrain.

Find out : Mathuraoil refinery is situatedvery close toTajMahal.Thesupremecourtissuedanordertoshiftittoafarawayplace.Why?

Reaction of water with metallic oxides

Whencalciumoxidereactswithwateritformscalciumhydroxide.

CaO+H2O→Ca(OH)2youmighthaveseenthisreactionwhenapasteforwhitewashingisbeingprepared.

Generallymetalicoxidesarebasic.

Deliquescent Substances

Youmighthaveseenjaggerybecomingmoistwhenexposedtoairforsometime.Therearemanysuchsubstanceswhichabsorbmoisturesuchasmagnesiumchloride,solidsodiumhydroxide,solidpotassiumhydroxide, anhydrous calcium chloride, calciumnitrate and Ferricchloride.

Activity 13.4

Take a dish and put some sodium nitrate and keep it exposed to air for 5-10 minutes. Observe the changes, Write your observations. Sodium nitrate becomes wet.

Potassium nitrate does not become wet when exposed to air. Can you give reason for this?

Definition

Certainwater-solublesubstances,whenexposedtotheatmosphereat ordinary temperature, absorbmoisture from the atmospheric airtobecomemoistandultimatelydissolveintheabsorbedwater.Suchsubstancesarecalleddeliquescentsubstancesandthephenomenoniscalleddeliquescence.

Trytheaboveactivitybyusingcausticsodaoranhydrouscalciumchlorideorwithsomechemicalfertilizers.Writeyourobservation.

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Examples of Deliquescent substances

Find out : Deliquescenceismorecommonincoastalarea.Why?

Know this : Compoundsthatcanremovewaterfromthesurroundingairarecalled ‘desiccants’ordryingagents.Concentratedsulphuricacidandcalciumchloridemonohydrateareexamplesfordesiccants.Weoftenfindsmall packs of solid desiccants placed inside electronic equipment or inmedicinetabletbottles.

Efflorescent substances

Certain hydrates lose water when exposed to air ofmoderatehumidity.An example is sodiumsulphate (Na2SO4.10H2O). The lossof water from hydrated compounds to the surroundings is calledefflorescence.Commonlyusedwashing soda is another example forefflorescentsubsranceRemoval of Hardness of Water

Water is a very common and suitable solvent. Some impuritiesdissolveinitveryeasily.MostlysolublesaltsofCalciumandMagnesiummakewaterhard.Asthepercentageofcalciumandmagnesiumincreasesinwater,thedegreeofhardnessalsoincreases.

Hard water

Hardwater doesnot producemuch latherwith soap.Generallywaterfromregionshavinglimestoneandothermineralrocksishardwater.calciumandmagnesiumbicarbonates,sulphatesandchloridesingeneralcausehardnessinwater.

Thesaltscausinghardnessarewatersoluble.Calciumcarbonatedoesnotcausehardnessbecauseitisinsolubleinwater.

Soft water

Softwaterproducesarichlatherwithsoap.Rainwaterandspringwaterareexamplesofsoftwater,sincetheycontainsmallamountofdissolvedsaltsinthem.

Think : Whyishardwaternotusedinindustrialboilers?

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Hardwatercontainscalciumandmagnesiumsalts.Ifitisusedinindustrialboilers,itformsinsolublesaltsofcalciumandmagnesium.Theyproducescaleon the innerwallsof theboilers,whichreducesheatingefficiency.Therearechancesof theexplosionof theboilers.Alsotherewillbecorrosionoftheboiler.

Soapwillbewastedinhardwater.

Methods of Removal of Hardness of WaterHardnessofwatercanberemovedbytwomethods:-

• IfhardwatercontainsCalciumandMagnesiumbicarbonates,itcanbemadesoftbyboiling.

Inthisreaction,Calciumbicarbonatedecomposestoinsolublecalciumcarbonateandcarbondioxide.

Example:Ca(HCO3)2heat CaCO3+H2O+CO2

• Hardnesscanberemovedbytheadditionofwashingsoda(Na2CO3)towater.Inthisreaction,thesolublesaltsofcalciumandmagnesiumareconvertedintoinsolublecarbonates.Thesolublesodiumsaltsdonotcausehardness.

Recall : Yourknowledgeofchemicaldoubledecompositionorexchange

Examples: CaCl2+Na2CO3→CaCO3+2NaCl

Ca(HCO3)2+Na2CO3→CaCO3+2NaHCO3

CaSO4+Na2CO3→CaCO3+Na2SO4

Activity 13.5

Write the equation of softening of water showing magnesium salts and sodium carbonate.

Activity 13.6

Experiment to show the removal of hardness by washing soda

Materials required :

1. beaker 2. glass rod 3. washing soda (sodium carbonate) 4. hard water

Take some hard water in a beaker and add a small quantity of washing soda to it. Stir it with a glass rod. Allow the insoluble carbonates to settle down or precipitate. Filter or decant the liquid.

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Water,soobtainedissoftwater.Butitisunfitfordrinkingasitcontainsexcessofwashingsodaandexcessofsodiumsalts.

Desalinisation plant : Desalinisation is an artificial process by whichsaline water (generally sea water) is converted into fresh water. It issuitable forhumanconsumption.Sometimes theprocessproduces tablesaltasaby-product.Thismethodwasinventedduringsecondworldwar.

Activity 13.7

Behaviour of Soap with hard water and Soft Water

Materials required: Hard water, 1 g of soap (from any transparent soap), 200 ml warm distilled water, 0.5 g of Epsom salt and washing soda. (Na2CO3)

Procedure: 1. Makeasoapsolutionbydissolvingabout1gofsoapin100mlof

warmdistilledwater.Allowthesolutiontocool.

2. Prepareasolutionofreallyhardwaterbydissolvingabout0.5gofEpsom(MgSO4)saltin100mlofdistilledwater.

3. Inatesttube,takeasmallquantityofhardwaterandaddthesoapsolutiontoitdropbydrop.Stiritwell.Whatdoyouobserve?Youmayobserveverylittlelatherbeingformed.

4. Inanothertesttube,takethesamequantityofthehardwaterandaddapinchofcrushedwashingsodaandshakevigorously.Allowtheprecipitatetosettle.Tothis,addthesoapsolutiondrop-by-dropandstir itwell.Whatdoyouobserve?Youwillfindthata largeamountoflatherisformed.

Dependingontheexactconcentrationsofyoursolutions,youwillfindthataftertheadditionofwashingsoda,latherisformedrelativelyeasily.Washingsodasoftenedthehardwater.

Allsaltywaterisnothardwater.Tryactivityno13.7withasolutionofsodiumchloridesolution.Youwillcometoknowthatsodiumsaltsdonotcausehardness.

Think : A person who is living at Kolar is using one kind of soap forwashing theclothes.Thesoap lasts foraweek.Anotherperson living inShimogaisusingthesamekindofsoap.Thatsoaplastsfor15-20days.Givereasons.Remembertheconditionsarethesamebutthekindofwaterusedisdifferent.

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Exercises :

I. Four alternatives are given to each of the following incomplete statement/question. Choose the right answer:

1. Magnesiumsulphatecrystalsarecommonlycalled.

a.gypsumsalt b.epsomsaltc.greenvitriol d.alum.

2. Whenyoubuywashingsodafromthemarket,youwillgetitinpowderformbecause

a.thecrystalsofwashingsodaquicklylosewatermolecules

b.theshopkeeperpreferstopowderthecrystals.

c.washingsodadoesnotformcrystals.

d.washingsodaisadryingagent.

3. Asampleofhardwaterisheatedinanutensil.Awhitedepositofcalciumcarbonateisformed.Thisisduetothepresenceof

a.calciumchloride b.magnesiumsulphate

c.calciumbicarbonate d.calciumhydroxide

4. TheSalt that causeshardness inwaterand that liberatescarbondioxideonheatingis,

a.magnesiumbicarbonate b.calciumchloride

c.magnesiumsulphate d.calciumsulphate.

5. When steam is passed over red hot iron we get the followingproducts.

a.ferrichydroxideandhydrogen

b.ferricoxideandhydrogen

c.ferroushydroxideandhydrogen

d.ferrousoxideandhydrogen

II. Fill in the Blanks with suitable words :

1. ChemicalnameofEpsomsaltis_________________.

2. Thechemicalusedtosoftenhardwateris_________________.

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III. Match the following : A B

1. causes scale a. calcium oxide

2. basic oxide b. soap

3. test for hardness of water c. sulphur dioxide

4. acidic oxide d. calcium bicarbonate

e. neutral oxide

f. does not react with water

IV. Answer the following :1. Water is tasteless, but we experience different tastes of water in

different places. Why?

2. Write balanced equations for the reaction of sodium, potassium and calcium on cold water.

3. What happens when steam is passed over red hot iron? Write the equation.

4. Definethetermsefflorescenceanddeliquescence.

5. Give two reasons to prove that water is a compound and not an element.

6. Name three metals which do not react with water, under normal conditions.

7. Name the products formed when the following oxides are dissolved in water. Write balanced equation.

a. Sulphur dioxide c. Carbon dioxide

b. Potassium oxide d. Calcium oxide

8. State the reasons for hardens in water.

V. Give reasons for the following :1. Sodium metal should be stored under kerosene.

2. Washing soda loses its crystal structure quickly.

3. When calcium nitrate crystals are exposed to air, a solution is formed.

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Chapter 14WOrLD OF SOUNDS

after studying this chapter students :• performexperimentstoshowthatsoundisproducedbythevibration

ofbodies.

• listthevariousfunctionsofsoundinourlife.

• describethemechanismoftransferofsoundthroughair.

• givejustificationtosaythatsoundisamechanicalwave.

• describeanexperimenttoshowthatsoundrequiresamaterialmediumforitspropagation.

• comparethespeedsofsoundthroughsolids,liquidsandgases.

• definethetermswavelength,frequency,amplitudeandvelocitywithrespecttoasoundwave.

• citeinstancestoshowthatsoundgetsreflectedfromsurfaces.

• describetheimpactofnoisepollutiononhumansandotherorganisms.

As you know,we see,we smell, we feel andwe taste.We alsohear.Everydaywehearahugevarietyofsounds.Soundallowsustocommunicatewithothers.Itcanbeasignalofdangerorsimplyanenjoyableexperience.Doallanimalshearsoundthesamewayaswedo?Itmaysurpriseyouthatwecannothearsomesoundswhichdogsorotheranimalscan.Whatissoundthen?Wecansaythatsoundisaphysicalsensationsensedbyourears.Whatourearscannotsenseisnotsoundforus.However,itmaybe‘sound’forotheranimals!

Think : There are many sounds, which we normally do not hear.The sounds of heartbeat, bowel, and air movement inside the lungsare examples of such sounds. Do you know what the doctors do tohear those soft sounds? How does the hearing of these sounds help?

Sound as a form of energy: Youhavelearntinyourearlierclassesthatsoundisaformofenergy.Whendowesaythatsomethinglikelightorsoundisaformofenergy?Youmayrecallthatenergyistheabilitytodowork.Cansounddowork?Ifitcan,then,wemaysaythatsoundisaformofenergy.Letusdosomeactivitiestoseewhetherornotsoundcandowork.

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Activity 14.1

Take a thin strip of paper. Hold it against sound from a loud speaker. Do you see any movement in the paper? What inference can you draw about sound from this activity? Think of more activities to show that sound does work.

Activity 14.2

Fig14.1Apersonusingamicrophone

If sound is a form of energy, it should be possible for us to convert it into other forms of energy. It should also be possible to convert other forms of energy into sound. Think of such situations in daily life. Have you seen a microphone? Figure 14.1 shows a common type of microphone. We speak into a microphone while addressing a large gathering. You feed energy into the microphone in the form of sound. What does a microphone do? What happens to the

sound inside a microphone? What happens in a loudspeaker? Do you know another device that transforms energy involving sound? Chapter 21 may help you answer some of these questions.

What conclusions can you draw from activity 14.1?

Functions of sound:While somesoundsarepleasing, someothersirritate.Therearesoundswecannothear!Imagineasilentworldwithoutanysound-noanimalsounds,birdcalls,nomusic,nogushingwater,nosoundofblowingwind.Wouldyoulovesuchaworld?Whataretheusesofsoundtousandtootheranimals?Makealist.Forinstance,howwillsoundhelpanimalstofindtheirfood?Howdoanimalsusesoundtoescapefromenemies?

Mimicry : Trytoimitatethesoundofdifferentanimals.

Soundcanbeasignalofalarmordanger.Soundmaybeareminderofsomethingweneedtodo.Itmaybeawayofdrawingattention,anexpressionofanideaoremotion.Itcanhelptograspideas.Listafewinstancesaboutfunctionsofsoundfromyourdailyexperience.Thinkofotherpurposesservedbysound.

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Nohornplease

Know this :Soundcandisturbothers.Haveyouseensignboardsliketheoneshowninthefigure?Wheredotheydisplaysuchboardsandwhy?Whyisitinhumannottofollowtheinstruction?

production of sound: Doyouknowhowweproducesoundwhenwetalk,whistleorsing?Howdoesabellproducesound?Whatcausesthesoundofathunder?Letusinvestigate.

Activity 14.3

Sit comfortably in a chair. Place one of your hands firmly midway on the throat. Say ‘ahhhh....!’ as long as you can. Do you sense anything at the fingertips? How does it feel to the hand while you produce the sound? Now change the kind of sound you produce. Instead of ‘ahhhh...’ you may now say ‘Uhhhhh....’. Make different kinds of sounds-loud, faint, shrill and soft. Feel the changes in the region of the throat. Did you notice any movements inside?

Activity 14.4

We have observed people play on instruments like veena, guitar, sitar and violin. How do these musical instruments produce sound? Make a list of musical instruments you know. Collect pictures of these instruments. Find out how each one of these produce sound. Record your observations in a suitable table.

Activity 14.5

Some of you may have music systems with box speakers at home. Take some ragi or mustard grains in a plate and place it on top of the speaker. Turn the music system on and observe the grains. What happened? Why did it happen? Steadily increase the volume and note the changes. What conclusions did you come to? Repeat this activity by placing the grains on a vibrating drum.

Activity 14.6

Take a rubber string. Stretch it tightly between two supports. Pluck the string. The string begins to vibrate. Note whether you can hear some sound. Stop the movement of the string. Did the sound also stop? Repeat this activity as many times as required. Try the activity with a metal wire. What inference can you draw from this experience?

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Activity 14.7

Start blowing air into a balloon. The balloon

Fig14.2Boyblowingaballoon

becomes bigger and bigger as in figure 14.2. Continue to blow until the balloon bursts. You suddenly hear a loud sound. From where did this sound come?

Whendomaterialsproducesound?Asyouknow,materialsgenerallyproducesoundwhentheymovebackandforthrapidly.Wecallsuchmotionas ‘vibration’.Therefore,wemaysaythatsoundisproducedwhenobjectsvibrate.Therecanbenosoundwithoutvibration.Thinkofsomemoreactivitiestoshowthatvibratingobjectsproducesound.Youmaynoteherethatsoundisproducedwhenthereissuddenexpansionorcompressionofgases.Forinstance,theburstingofaballoonmakesa loudsound.Thinkofothersituationswheresuddenexpansionofairoranygasproducessound.Asmoothflowofgasesaroundbluntobstaclescanalsoproducesound.Forinstance,wegetsoundwhileblowingatrumpet.Inanycase,somethingwillvibratetocausesound.

Nowletusunderstandhowweproducesoundwhenwespeakorsing.Wehaveaspecialapparatuscalled‘voicebox’.‘Larynx’istheothernameforvoicebox.Thissystemhelpsustoproducesound.

Fig14.3PositionofLarynxinourbody

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Voiceboxislocatedattheupperendofthewindpipe.Therearetwomembranesinthevoicebox.Thesemembranesarecalledvocalcords.Theystretchacrossthevoicebox.Thestretchingleavesasmallgapbetweenmembranesintheformofanarrowslit.Theslitcontrolsthepassageofair.Whenwewishtoproducesound,wepushairthroughtheslit.Thiscausesthevocalcordstovibrate.Thevibrationsofthevocalcordsproducesound.Themusclesattachedtothevocalcordshelptoloosenortightenthevocalcords.Thisenablesustoproducesoundsofvariousqualities.Theactualmechanismismorecomplicatedthanthis.

Find out : Youmighthavenoticedthechangeinvoiceduringcoughandcold.

how does the sound reach us from the source?

Fig14.4Propagationofsound

How does sound travel from thesource towards our ears? Tounderstand this, let us recall anexperience familiar to all. Let usimaginethatwehavethrownastoneinto a pool of still water. Circularwavesspreadrapidlyoverwaterandtheytravelinalldirections.Dowaterparticlestravelawayfromthepoint

ofdisturbance?Youcancheckbyplacingafewgrainsofsawdustoverthesurface.Theydonottravelaway.Instead,theymerelymoveupanddownintheirownposition.Soundtravelssimilarlyintheformofwaves.Seefigure14.4.However,thevibrationofparticlesofthemediumwillbeinthedirectionofthesoundwaveitself.

Nature of sound:We have learnt that vibrations can producesound.Therefore,soundisakindofmechanicalenergy.Whatmoveswhensoundtravelsthroughamediumsuchasair?Anyenergymovesthroughamediumbycreatingadisturbanceinit.Thesedisturbancesmayrepeatthemselvesatregularintervals.Suchperiodicdisturbancesconstituteapattern.Wecallthispatternofdisturbanceaswaves.Soundalsotravelsthroughamediumintheformofwaves.Whatisthenatureofsoundwaves?Letusdoanactivitytounderstandthis.

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Activity 14.8

You might have played with a toy spring. We call it ‘slinky’. Fix one end of a slinky firmly to a support on a table or floor. Hold the other end in your hand. Now give pushes to the slinky back and forth along its length. Observe the pattern in the slinky. Refer figure 14.5 to get an idea of the pattern you see in the slinky. You observe, in some places of the slinky, the rings coming closer. We call this as compression.

Between two compressions, you also see the rings moving apart. We call this rarefaction. You observe alternate compressions and rarefactions all along the slinky. Observe the movement of the compressions and rarefactions. It appears as though the compressions and rarefactions are moving away towards the other end. Is it really so?

Check by tying a thread to one of the rings. Is the thread moving towards the other end? Then what is moving here?

Fig14.5Alternatecompressionsandrarefactionsallalongtheslinky

Fig14.6Propagationofsoundthroughairandrepresentaionofasoundwave

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Observetheslinkyagain.Thethreadtiedtooneoftheringsmovesbackandforthalongthelength.Anymotionofthistypeislongitudinalmotion.Awavecausedbysuchmotionofparticles isa longitudinalwave.Letusnowreturntosoundwaves.

Imaginethatyouarelisteningtomusicfromaspeaker.Thesoundfromthespeaker transmitsenergyto thesurroundingmedium.Thesurroundingmediumhereisair.Theenergycausestheairparticlestocompress.Thecompressedparticlestransmittheirenergytothenextneighbouringparticles.Theprocesscontinues.Thus,therewillbeseveralcompressionsandrarefactionsinairbeforethesevibrationsreachyourear.Observefigure14.6togetanideaastohowthishappens.Youmaynotehereagainthatthevibrationofparticlesisparalleltothedirectionofsound.Fromthis,wemayconcludethatsoundisalsoalongitudinalwave.Soundisamechanicalwaveasitinvolvesvibrationofparticles.fig.14.6showsthetypicalwayofrepresentingawave.

Wejustlearntthatwhensoundtravels,theparticlesofthemediumvibrate.Whathappenswhenthereisnomediumatall?Cansoundtravelintheabsenceofamedium?Letusexplorethisthroughanactivity.

Know this : Thereare transversewavesalso. In this typeofwaves theparticlesofthemediumvibrateperpendicularlytothelineofpropagation.Examplewaterwaves.Youwillstudymoreaboutsuchwaves inhigherclasses.

Activity 14.9

Suspend a mobile phone inside an

Fig14.7Experimenttoshowthatsoundcannottravelinvacuum

airtight glass bell jar as shown in figure 14.7. Connect the bell jar to a vacuum pump. When you call the phone number you can hear the ring tone. Now remove the air from the bell jar by using the pump. Observe the phone and the changes in the sound. What happens to the strength of sound? Why cannot you hear the sound after some t ime? What conclusion can you draw from this experiment?

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We have learnt that sound travels through gases. Can sound travel through solids and liquids too? In which of these media does the sound travel better? Let us investigate.

Activity 14.10Place your ears firmly on a wooden table. Ask a friend to scratch the table

at the other end. Did you hear the scratching? Raise your head so that the ear is about 10 cm above the table. Now ask the person to scratch again. Did you now hear the scratching? In which case do you hear the scratch loudly? Which medium conducts sound better: air or wood? Think of an activity to find out whether sound travels through a liquid medium such as water.

How do Dolphins and whales which live in water communicate? They produce and use different kinds of sounds and whistles. These sounds travel through water and pass on messages to others. Some species of dolphins send special sounds to identify themselves.

Description of a sound wave:Allsoundwavesaresimilarincertainrespects.However, theymay differ in certain characteristics. Howcanwedistinguishbetweenthemanddescribethem?Weusecertaincharacteristicsofawavetodescribeit.Thisistrueofallwavesincludinglight andwater waves. These characteristics include wavelength,frequency, amplitudeand speed. Letusunderstand themeaningoftheseterms.Wavelength:Wehavelearntthatsoundisalongitudinalwave.Thismeansthattheparticlesofthemediumthroughwhichsoundtravelswillshowaseriesofcontractionsandrarefactions.Theparticlesofthemediumvibratebackandforthinthedirectionofthesounditself.

Fig14.8Wavelength

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The distance between two successive compressions is thewavelength ofthesoundwave.Seefig.14.6Thiswillbesameasthedistancebetweentworarefactions.Ithelpstorepresentthewavelengthbyasymbol.Themostcommonlyusedsymbolforwavelengthisλ.ItisaGreekalphabet.Wemustreadthissymbolas‘lamda’.Wavelengthactuallyrepresentsthelengthofonewave.Differentsoundsmayhavedifferentwavelengths.Frequency:Thenumberoftimesanobjectvibratesinonesecondiscalledfrequency.Frequencyofasoundwaveissameasthefrequencyofthesource.Fasteranobjectvibrates,higherwouldbeitsfrequencyandthefrequencyofsounditproduces.

Letusunderstandfrequencyinanotherway.Thepropagationofsoundinvolvesthetravellingofadisturbanceintheformofcompressionsand rarefactions. Thenumber of compressions that pass throughapoint inonesecondwillalsogive the frequency. If40compressionspassthroughapointinonesecond,then,wesaythatthefrequencyis40hertz.Thismeansthat40wavelengthsarepassingthroughagivenpoint inonesecond. If200compressionspassthroughapoint in2second,whatwillbethefrequency?Howmanywavelengthswouldbepassingthroughinonesecond?Theinternationalunitoffrequencyis‘hertz’.Weusethesymbol‘Hz’torepresentit.

1hertz[Hz]=1wavepersecondorcyclepersecond

Know this : Theproductof frequencyandwavelengthofawave is thevelocityofthewaveinthemedium.

Velocity=frequencyÍ wavelength

amplitude: Amplitude is another important physical quantity of allwavesincludingsound.Thehighestdisplacementofaparticlefromitsrestpositionistheamplitudeofthesound.

Amplitudeofanywaveincludingsoundisthe‘height’ofthewave.Youunderstandthiswellwhenyoureferfig.14.8.Higheramplitudescausehighervolumeofsound.ReferChapter21.Amplifierisadevicethatincreasesamplitudeofawave.Activity 14.11

Look at fig.14.9. It shows three waves A, B and C of different amplitudes. Assume that these are sound waves. Which of them has the highest amplitude? Which of them has the lowest amplitude? Which one of these waves is the loudest?

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Fig14.9Waveswithdifferentamplitudes

Speed of sound: Youhave studied elsewhere that light travelsmuchfasterthansound.Youmayrecall that lightningandthunderoccursimultaneously.However,weseethelightningfirstandhearthesoundofthunderalittlelater.Howfastdoessoundtravelthroughamedium?Weexpressthis intermsof ‘speed’.Speedofsound is thedistancetravelledbyitinonesecond.TheS.I.unitofspeedis‘metrepersecond’.Wewritethisasms-1.

Know this : Thespeedofsoundthroughairat250Catsealevelis346metrepersecondor0.346kmpersecond.Evenmostjetairplanesdonottravelthatfast.Whenaplanetravelsfasterthanspeedofsound,theplanebreaksthesoundbarrierandproducesaloudsound.Thisissonic boom.OnOctober14,1947,ChuckYeagerdidjustthatinasmallplanecalledtheX-1.Hewasthefirstpersontoflyfasterthanthespeedofsoundandthelistenersonthegroundwerethefirsttoheartheloudshockwaveofthesonicboom.

echo:Whathappenswhenlightfallsonanobstacle?Atleastapartofitundergoesreflection.Whathappenswhensoundwavesstrikeanobstacle?Dotheyalsocomebackfromthesurfacethewaylightdoes?Letusinvestigate.

Activity 14.12

Have you heard an echo? Sometimes it happens in big rooms and near the hillside. If you have visited Gol Gumbaz, in Bijapur of Karnataka you will surely appreciate echo effect. How does this happen? Look at figure 14.10. There are two identical

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cardboard tubes P and Q. Place tube P at an angle to a metal surface AB. Place a screen S between the two tubes. Keep a small clock at the other end of tube P. Place the other tube Q close to the metal surface at an angle. Bring your ear near the free end of tube Q. Do you hear the tick-tak of the clock? If not, slowly change the position of the tube Q. At some fixed position, you will hear the sound of the clock clearly. How could you hear the sound through tube Q? Recall a similar experiment you did while studying about light.

Find out : What should be the minimum distance between a personshoutingandreflectingsurfacetoheartheecho.?

Fig14.10Reflectionofsound

Whenyoushoutinsideanemptyhall,youhearyourownsoundaftersometime.Thisisduetoreflectionofsound.Surfaceofobstaclessuch aswalls,mountains, clouds or land reflect soundwaves. The‘rolling’ of thunder is largely due to successive reflections from theclouds.Whathappensinsidebuildings?Furniture,windows,curtainsandothermaterialsabsorbsoundtosomeextentandreducereflections.Itisimportanttoavoidsuchreflectionsinsidetheatresforclearsound.Reflectionofsoundfindssomewonderfulapplicationsinfieldssuchasindustry,medicineandentertainment.Youmaybeexcitedtoknowaboutthem!

Noise and its hazards:Wedonotlikeallsounds.Somesoundscausedisturbancetohumansandotheranimals.Wecallallsuchunwantedsoundsasnoise.Anyexcessivesoundthatcausedisturbancetohumanandanimallifeleadstonoisepollution.Suchsoundsmaycomefromone

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ormoreofseveralsourcessuchaspeople,machinesoranimals.Motorvehicles, horns, loudspeakers, construction and transport systems,aircraftmovements,railnoisemaybequiteunpleasant.Sirens,musicsystems,radioandfireworksmayalsocausesoundpollution.

Loud sounds may cause irritation, headache and loss ofconcentration.Longexposuretosuchsoundsmayleadtolossofsleep,tensionandstress,highbloodpressure,heartproblemsandhearingloss.Noisecausesmanyadverseeffectsonanimals.Forexample,noiseisadisadvantageforbirdsthatrelyonhearingtolocateprey.

Find out : Collect information about methods of prevention of noisepollution.

Soundispresenteverywhere.Wereallytakenoteofitandcomplainaboutitonlywhenitistooloudortoosoft.

exercises :I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Imaginethatyouarelisteningtoapopularsongfromaradio.Usingvolumecontrolknob,youslightly increase thevolume.The factorrelatedtosoundwaveinthisprocessis,increasein

a.frequency b.velocity

c.amplitude d.bothfrequencyandwavelength

2. Thevelocityofsoundishighestin

a.air b.water c.glass d.vacuum

3. Inanunoccupiedhallofachoultryyouwillexperiencetheechoeffectofsound.Ifthesamehallisfurnishedwithalmirahs,tables,chairs,andothercommodities,youmaynotexperiencetheechoclearly.Itisbecause,

a.soundwavesgetabsorbedbytheobjectsinthehall.

b.theareaofreflectingsurfacedecreases

c.reflectedsoundisreflectedagain.

d.sounddoesnotgetreflected

4. Thefactorthatistransmittedinwavemotionis,

a. particlesofthemedium b.vibrationsofparticles

c. energyofthecauseofthewaved.electronsofthemedium

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II. Fill in the Blanks with suitable words :

1. Theproductoffrequencyandwavelengthofasoundwaveisequaltoits____________________.

2. TheSIunitofwavelengthis___________________.

3. Thevelocityofsoundinairat250Cisapproximately_____________.

III. answer the following :

1. Whyissoundalongitudinalwave?

2. Explainanactivitytoshowthatsoundcandowork.

3. Describeanactivitytoshowthatsoundisproducedbyvibrationofmaterials.

4. Make a list of fivemusical instruments. State how each of themproducesound.

Musicalinstrument Thewayitproducessound

5. Listtwoapplicationsofreflectionofsound.

6. Describeanactivitytoshowthatsoundrequiresamaterialmediumforitspropagation.

7. Representawavegraphically.Showinthediagram,the wavelengthandamplitude.

think :

1. Whyissoundbothaboonandbane?

2. Whatmeasureswouldyoutaketominimizethesounddisturbancecausedtoothers.

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Chapter 15 heat

after studying this chapter the students :• definethetermsheatandtemperature.

• describetheeffectofheatonsolids,liquidsandgases.

• mentiontheapplicationofexpansionofsolids,liquids,gasesindailylife.

• namethedifferenttypesoftemperaturescales.

• listtheadvantagesofmercuryinthermometers.

• convertCelsiusscaleoftemperaturetoFahrenheitscaleoftemperatureandvice-versa.

Youhavestudiedearlierthatheatisaformofenergy.Weuseitforseveralpurposes.Forinstance,weuseheatforcookingfood.Forwhatelsedoweuseheat?Makealistofactivitiesthatrequireheat.Letusstudymoreaboutheatenergy.

Activity 15.1

Take a cup of water. put a drop of ink into the water. What happens? Why does the ink spread? It is due to the movement of the molecules.

Activity 15.2

Open the cap of a perfume bottle in the corner of a class room. How does the fragrance spread all over the room?

Youknowthatallmatterismadeupofatomsandmolecules.Theyarealwaysinmotion.Hencetheyhavekineticenergy.Thetotalkineticenergyofallthemoleculesinasubstanceiscalledheat.TheS.Iunitofheatisjoule(J).Ifweheatthesubstance,weareaddingenergytothesubstance.Thisaddedenergycanberealisedasan increase intheaveragekineticenergyof themolecules.Themoleculesnow,onanaverage,havemorekineticenergy.Thisincreaseinaveragekineticenergyiscalledtemperature.temperature

Wehavebeenfamiliarwiththesensationsofheatandcoldsincechildhood.Insomesituationsbytouchingtheobjects,wefindoutwhichoneisrelativelyhot.Torealizethis,letusperformthefollowingactivity.

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Activity 15.3

Pour hot water,water at room temperature and ice cold water into three separate glass tumblers. Dip the index finger of one hand in the ice cold water and that of the other hand in the hot water. Hold the fingers in the water for some time say about a minute. Then dip both the index fingers into the water at room temperature.

Is the water hot or cold? You will observe that the finger which was previously in contact with hot water will now feel cold. Whereas the other finger feels hot.It shows the sensation of degree of heat or cold. The measure of degree of heat or cold of a substance is called temperature.

Activity 15.4

Take 100 cm3 of water and 200 cm3 of water at the same temperature in two separate beakers. Which has more heat? The heat depends on the mass of the substance. Boil the water in both the beakers. Note the temperature. Are the temperatures in the two beakers the same?

Temperature does not depend on themass of the substance atagiven temperature.But it isanumber that is related toa typeofenergy possessed by themolecules of a substance. Temperature isrelatedtothekineticenergyofthemolecules.Afterunderstandingheatandtemperature,nowletusstudythedifferencesbetweenheatandtemperature

table 15.1 Difference between heat and temperature

heat temperature

Heatisaformofenergy Temperatureisameasureofthedegreeofhotorcold.Itisanumberthatisrelatedtoenergy,butitisnotenergyitself.

Heat energy depends upon thespeedoftheparticles,thenumberofparticlesandthesizeormassand the type of particles in anobject.

Temperature does not depend onthesizeormassofanobject.Forexample, temperature of a smallcup of water is the same as thetemperatureofatubofwater,Butthe tub of water hasmore heatbecauseithasmorewaterandthusmoretotalthermalenergy

S.IunitofheatisJoule S.IunitofTemperatureisKelvin

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effects of heat:Ifweprovideheattoasubstanceitstempeatureincreases. Now let us study more about the effects of heat.

Activity15.5

Fig15.1Expansionofgases

Take an injection glass bottle and insert a pen refill as shown in fig 15.1. Put a drop of water at the top of the refill. Hold the bottle tightly. What do you observe? Why is water pushed out from the tube?

Activity15.6

In this chapter you will come across the measurment of temperature using

thermometer. Why does the mercury level rise above the red mark in case of a person having fever ? Can you give reason ? This is the best example to show that liquids expand after heating .

Activity15.7

Take two aluminium rods measuring 7 cm

Fig15.2ExpansionofSolid

each. Fit it and connect it as shown in fig.15.2. Keep paper thin gap between the rods. Now heat the rod. What happens? Why does the bulb glow? Remove the flame. What happens? Why does the light go off?

Whatisyourconclusiononthebasisofaboveactivities?Heatenergyresultsintheexpansionorcontractionofsolids,liquidsandgases.

Letusstudytheothereffectsofheat

Activity15.8

Take a block of ice in a 20 cm3 beaker. Heat it. What is the change observed? Continue heating till water begins to boil. Observe that the level of water decreases. What can we conclude?

Activity 15.9

Take 10 g of wax in a 20 cm3 beaker and do the experiment as explained above. What conclusion do you draw? Heat energy can bring about a change in the state of a substance.

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Activity 15.10

Take one spatula of potassium permanganate in 20 ml test tube. Heat it. Introduce a glowing splinter inside the tube. What do you observe? Why is the glowing splinter rekindled?

Activity 15.11

Take a cup of water. Note the temperature. Heat the cup for 10 minutes. Note the temperature. What is your conclusion? Heat energy brings about a change in temperature

Expansionofsolidsonheatingplaysanimportantroleinourlife.Insomecasesitisdisadvantageouswhereasinsomecasesitisveryuseful.

problems caused by the expansion of solid by heating1. Ifweputboilingwaterinathickglasstumbler,itcracksimmediately.

Thisisduetothefactthatglassisapoorconductorofheat.Whenboilingwaterisputintheglasstumblertheinnersurfaceoftheglassbecomeshot.Sothewallexpands.Buttheoutersurfaceoftheglasswalldoesnotexpandquickly.Thisunevenexpansioncrackstheglass.Thisproblemcanbeovercomebychoosingaverythinglasstumblerwithlowexpansioncapacity(Pyrexglassorborosilicateglass)

2. Haveyouobservedcementedroads?Whyisthespaceleftbetweenthesmallstretches?

3.

Fig15.3Loopofmetalpipe

Inindustries,hotwaterormoltenliquidistransferredfromoneplacetoanotherthroughmetalpipelines.The expansion and contractionmightbendorbreakthepipe.Toover come this, these metalpipelinesareprovidedwithloopsatregularintervals.Theexpansionofpipelinecausesthesizeoflooptoincreaseslightly.Sopipedoesnotbreak.Seefig15.3.

Listsomeoftheotherproblemscausedbytheexpansionofsolids,liquidsorgases.

Expansionofsolids,liquids,gasesplaysanimportantroleinourlife.

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Let us see some of the useful applications

• Thermalexpansionofbimetallicstripsfindmanyapplications.

It is used as aheat operated switch in the circuit of automaticequipmentslikeironbox(fig15.4)firealarms,electricheaters,microwaveoven,refrigerators,incubators

Fig15.4Ironbox

andairconditioners.

• Somethermometersworkontheprincipleofexpansionofliquids.

• In automobile engines usefulworkisdonebytheexpansionofgases.

anomalous expansion of water

Wateroncoolingcontractsupto40C.Afterwardsitstartstoexpandtillitfreezesintosolidiceat00C.Thisunusualpropertyofwaterbetween00Cto40Ciscalledanomalous expansion.Insimplewordswaterat40Cexpandswhenheatedandexpandswhencooledalso.

Incoldcountriesasthetemperatureofairfallsbelow00Cthewaterinponds,lakes,riversandseafreezeatthetoptoformsolidice.Butbeneath,theicewaterstaysat40C.Sofishandotheraquaticlifecaneasilysurviveinwaterevenwhenthetemperatureofairfallsto00C.Theexpandedwaterwhichwillbeintheformoficehascomparativelylowerdensityandfloatsonwaterandactslikeinsulatortomaintainthetemperatureofliquidwater.

Wehavealreadystudiedaboutheatandtemperature.Nowwelearnabout themeasurement of temperatureusing an instrument calledthermometer.

thermometer: Thermometer is an instrument thatmeasures thetemperatureofasystemquantitatively.

Youmighthaveobservedamothersensingthetemperatureofherbabybygentletouchofhand.Thispracticedoesnotgivequantitativemeasurementoftemperaturebutgivesanapproximatecomparison.

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Measurement of temperature

Most of the thermometersmeasure temperature bymakinguseofpropertyofexpansionofliquidsonheating.Agivenlengthofliquidnamelymercury column increases with increase in temperature.Thermometersarecommonlyusedinourdailylife.Nowadays,therearedigitalthermometersalso.

Laboratory thermometer

Fig15.5Laboratorythermometer

Laboratory thermometers areused tomeasure temperatures ortemperaturechangeswithahighdegreeofprecision.Theyaremadeofmetalorglassandstrengthenedthroughprocessessuchasthermaltemperingorannealing.Severaltypesoflaboratorythermometersarecommonlyavailableinthemarket.Liquid-in-glassthermometersaremadeofsealedglassandcontainafluid,usuallymercuryorredcolouredalcohol,whosevolumechangesrelativelytoitstemperature.Bimetallicstripthermometersincludetwodifferentmetalsthatarebondedtogetherandexpandatdifferentratesastheywarmup.Often,longbimetallicstripsarewoundintoacoilandusedwithadial.

Clinical thermometer

Aclinicalthermometerisdesignedforclinicaluseinhumansoranimals.Itismadeofafinecapillarywithabulbfilledwithmercuryatoneend.Nearthebulb,ithasanarrowbendknownasconstriction.Clinicalthermometerscanbeinsertedintothemouthorarmpit.Itcanpreventthebackflowofmercurywhenit istakenoutofapatient’smouthorunderarm.Beforeuse,thethermometerisjerkedsothatthemercuryflowsbackintothebulb.

Toreducetheriskofcross-contaminationbetweenpatientsithastobesterilisedaftereachuse.

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Fig15.6Clinicalthermometer

Observe the fig. 15.6 andnote two special features of a clinicalthermometer.

Thenormaltemperatureofthehumanbodyisabout370Cwhichisequivalentto98.60F.Ourbodytemperaturecannotfallbelow350Corriseabove420C.Hence,therangeofclinicalthermometerisbetween350Cand420C.

Think : Watercannotbeusedasaliquidinathermometer.Why?

precautions to be taken while using a clinical thermometer:• Thermometer should be washed before and after each use,preferablywithanantisepticsolution.

•Donotwashthethermometerwithhotwater.•Ensurethatbeforeusethemercurylevelisbelow350C.•Readthethermometerkeepingthelevelofmercuryalongthelineof sight.•Handle the thermometer with care, as you handle any glass articles.•Don’tholdthethermometerbythebulbwhilereadingit.

Activity15.12

Measure the body temperature of some of your friends (at least 10) with a clinical thermometer. Record your observations. (do this activity by keeping the thermometer under arm pit)

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Think : Whyshouldwekeepthethermometerunderarmpitforinfants,oldagepeopleandpeoplewithmentaldisabilities?

temperature scales

Therearethreecommonlyusedscalesoftemperature.

• Celsiusscaleoftemperature

• Fahrenheitscaleoftemperature

• Kelvinscaleoftemperature

The temperature is generallymeasured in degreeCelsius. It isdenotedas0C.

Thereisanotherunitoftemperaturenamely,degreeFahrenheit,whichisdenotedas0F.

TheS.I.unitoftemperatureisKelvin(K).

Diagram showing comparison of temperature scales

Fig15.7Comparisonoftemperaturescales

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InCelsiusscale,oftemperaturethemeltingpointoficeistakenaszerodegreeandtheboilingpointofwateris100degreeandthedistancebetweenthetwoisdividedinto100equalparts.

On theFahrenheit scale of temperature themeltingpoint of iceistakenas32degrees.Theboilingpointofwater is212 0Fandthedistancebetweenthetwoisdividedinto180equalparts.Eachdivisioncorrespondsto1degree.

InKelvinscaleof temperature, themeltingpointof ice is273Kandtheboilingpointofwateris373K.AsintheCelsiusscalethereare100gradationsbetweenthesetwopoints.HencetheKelvinscaleoftemperatureissimilartoCelsiusscaleoftemperature.

anders Celsius (1701-1744) TheCelsius sacle of temperaturewas earlierreferredasthe“centigrade”scale.TheCelsiusscalewas developed by Swedish AstronomerAnders Celsius. It has 100 equal divisionsbetween the freezing point (0 0C) and boilingpoint (100 0C)ofwater.Therefore it isknownas centigrade scale. The term “Celsius” wasadoptedin1948byaninternationalconferenceonweightsandmeasures.

AndersCelsius

Think : Mercury thermometer is not suitable for measuring very hightemperature why? Alcohol is used as thermometric liquid to measuretemperaturebelow380Cwhy?

Conversions• ToconverttheCelsiusscaleoftemperatureintoKelvinscaleof

temperature,wehavetoadd273totheCelsiusscaleoftemperature.Forexample,00Cisequivalentto0+273=273K.

• ToconverttheKelvinscaleoftemperaturetoCelsius,wehavetosubtractgivenKelvinscaleoftemperaturefrom273.

Forexample77Kisequivalentto77-273=-1960C

Letusstudyhowtousethethermometertofindtheboilingpointofwaterandmeltingpointofice.

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Activity 15.13

To find the boiling point of water.

Fig15.8Boilingpointofwater

Takeabout50cm3ofwaterinaround-bottomflaskandaddafewfragmentsofbrokenporcelain.Heattheflaskandnotethetemperaturewhenboilingbegins.Takereadingseverythirtysecondsforfiveminutes,i.e.tenreadingsinall,andtaketheaverageastheboilingpoint.

Do this : Addsodiumchlorideandfindtheboilingpointinthisactivity.

Presence of soluble salts inwater increases the boiling point.Similarlypressurealsohasaneffectonboilingpoint.Tomaintainthepressureatsamelevelsteamoutletisnecessary.Usuallyadditionofsolublesaltincreasestheboilingpointofthesolvent.

Inpressurecookerstheboilingpointofwaterincreasesduetothepressurecreatedbyblockingofthesteambyweight.Theweightrisesupandletsoutthesteamifpressurecrossescertainlimit.

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Activity 15.14

To find the melting point of ice :

Fig15.9Experimenttofindmeltingpointofice

Smallicecubesaretakeninafunnel.Funnelisfixedtoastandasshowninfig.15.9Thermometerbulbiskeptinthefunnelsuchthatitissurroundedbyicecubes.Keepaglassbottlebelowthefunnel.Icebegins tomeltutilising theheatof thesurroundingair.Water thusformeddropsoutofthefunnel.After10minutesnotedownthelevelofmercuryinthethermometerandtakethereadingwhichshowsthemetingpointofice.

Averagemeltingpointandboilingtemperaturesofsomecommonsubstancesareindicatedinthetablebelow:

Find out : Arethereanyfactorswhichinfluencethefreezingpointofasubstance?ConductactivityNo15.14byaddingcommonsalttoice.Whatisyourconclusion?

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table 15.2. Melting point and Boiling point

SubstanceMeltingPoint

Temperature(oC)BoilingPoint

Temperature(oC)

Aluminum 659 2,327

Copper 1,083 2,595

Gold 1,063 2,600

Mercury -38.8 357

Nitrogen -210 -196

Oxygen -219 -183

Water 0 100

Convert the boiling and themelting points of the above givensubstancesintoKelvinscaleoftemperature.

exercises :

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Whenanobjectisheated,themoleculesthatmakeuptheobject

a.begintomovefaster b.loseenergy

c.becomeheavier d.becomelighter

2. Thetemperatureofabodyisanindicatorof

a.Thetotalenergyofthemoleculesofanobject

b.Theaverageenergyofthemoleculesofanobject

c.Thetotalvelocityofthemoleculesoftheobject

d.Theaveragekineticenergyofthemoleculesofanobject

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3. AandBaretwoobjects.ThetemperatureofAisgreaterthanthatofB.Thismeansthat

a.themoleculesofAmovefasteronanaveragethanthemoleculesofB

b.thetotalenergyofAisgreaterthanthetotalenergyofthemoleculesofB

c. the average potential energy of A is greater than the averagepotentialenergyofB

d.theheatcontentofAwillalwaysbegreaterthanthatofB

II. Fill in the blanks with suitable words:

1. Thedegreeofhotorcoldofabodyiscalled_________________(heat/temperature)

2. Temperatureisexpressedin___________(degreecentigrade/joule)

3. Whenabodychangesfromliquidtogasatconstanttemperature,itiscalled_______________________(condensation/boilingpoint)

4. ThetemperatureofboilingwaterintheCelsiusscaleoftemperatureis_____________0C(100/373/212/32)

5. TheS.Iunitofheatis________________(Joule/Celsius)

III. State whether the following statements are true or false :

1. Liquidsexpandonheating.

2. Theunitofheatandtemperaturearethesame.

3. Bimetalstripisusedinfan.

IV. answer the following :

1. Distinguishbetweenheatandtemperature.

2. Mentionthreedifferenteffectsproducedbyheat.

3. Giveoneexampletoillustratethatheatcanbegeneratedfromtheenergyofmotion.

4. Describeanexperimenttoprovethatsolidsexpandonheating.

5. Nametwodeviceswhichusebimetallicstrip.

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6. Athickglasstumbleroftencrackswhenboilingwaterispouredintoit.why?

7. Statesimilaritiesanddifferencesbetweenthelaboratorythermometerandtheclinicalthermometer.

8. Convert1000FintoCelsiusandKelvinscaleoftemperature.

V. Match the following :

A B

1. formationoficebergs a. kelvinScale

2. riseofmercurylevelin b. suddenContractionthermometer

3. automaticelectriciron c. celsiusScale

4. crackingofhotglassplate d. boilingPoint

whentouchedbycoldobject. e. bimetalStrip

f. thermalexpansion

g. anomalousexpansionofwater

project Ideas :1 Meetaveterinarydoctor(adoctorwhotreatsanimals).Discussand

findoutthenormalbodytemperatureofdomesticanimalsandbirds.

2 Collectinformationaboutthefollowingmeasuringinstruments:micrometer, screw gauge, vernier callipers, spring balance, barometer,ammeter, voltmeter, hygrometer and lactometer.Write a reportexplainingtheuseofeachoftheseinstruments.

4 Writeareportonthehistoryofmeasurementsystemsusingbooks/internetforreference.

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Chapter 16

StateS OF Matterafter studying this chapter students :

• classifymaterialsintosolids,liquidsandgases.

• statethecharacteristicfeatureofaphysicalchange.

• appreciatemoleculararrangementingases.

• givereasonastowhywaterandoildonotmixwitheachother.

• definethetermdensity.

• conductsimpleexperimentsrelatedtodensity.

• definethetermspecificgravity.

Lookattheobjectsaroundyou.Someareinsolidstate,afewareinliquidstateandafewothersareingaseousstate.Whatarethesemadeof?Alltheseobjectsandmaterialsaremadeofmatter.Whatismatter?

Youareawarethat“Anythingthatoccupiesspaceandhasmassiscalledmatter.”Activity 16.1

Make a list of materials around you. Classify them as solids, liquids and gases as shown in the table.

Sl. No. Solids Liquids Gas

1 Brick Milk Air

2

3

4

5

Howcanweknowthatmatteroccupiesspace?Letusdosomesimpleactivitiestoexplorethis.

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Activity 16.2

Keep a glass tumbler in a plate. Fill the tumbler with water up to its brim. Lower gently a stone into the tumbler. Observe the water in the tumbler. What happened? Why did the water spill out of the tumbler?

Activity 16.3

Take water in a trough. Invert a glass tumbler in water and hold the glass pressed inside water. Observe whether there is water inside the tumbler. Now slightly tilt the tumbler. Observe the water level inside the tumbler. Keep on increasing the tilt of the tumbler and note the gradual increase in the water level. What does this activity demonstrate?

Fig16.1Diagramshowingthatairoccupiesspace

Dogasesoccupyspacejustthewaysolidsandliquidsdo?Letusexplorewiththehelpofanactivity.

Blowaballoon.Airblownoutofyourmouthhasfilledintheballoon.Sogasesalsooccupyspace.

Whatcanweconcludefromtheaboveactivities?Allmatteroccupiesspace.Itistooobviousthatsolidsandliquidshavemass.Dogaseshavemass?Letusfindoutwiththehelpofanexperiment.

Activity 16.4

Take two identical football bladders. Blow air into one of them with the help of a pump. Keep one of the bladders on a pan of a sensitive balance. Keep the bladder bloated with air on the other pan. Compare the masses. Which of them is heavier?

Basedontheactivitieswehaveconducted,wecangeneralizetwopropertiesofmatter.Matterhasmass,occupiesspaceandhasweight.Thisistrueforsolids,liquidsandgases.

Canwechangethephysicalstateofasubstance?Canwechangeasubstanceinsolidstatetoliquidstateorvapourstate?Isthischangereversible?Tounderstandthis,weshalldoanactivity.

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Activity 16.5

Take a few ice cubes and heat them in a container. Ice changes into liquid state and becomes water. On further heating, water changes into steam. Steam is water in vapour state. What happens if steam is cooled?

Hence,watercanbechangedfromitssolidstatetoitsliquidstateandlatertoitsgaseousstate.Thisisareversibleprocess.Inthisactivity,nonewsubstanceisformed.Onlythephysicalstateischanged.Thusthechangeofphysicalstateofasubstanceisaninstanceofphysicalchange.Werepresentthischangeasfollows:

Ice water steam

Canyou thinkof other substanceswhosephysical state canbechanged?Howcanyouachievethis?Canwechangethephysicalstateofagas?Howdoweachieveit?

Weallknowthateverymatterismadeupofminuteparticlescalledatomsandmolecules.Letusseehowthemoleculesarearrangedinsolids,liquidsandgases.

Fig16.2Arrangementofmoleculesinsolids,liquidsandgases

Observe the above figure, closely look at the arrangement ofmoleculesinsolids,liquidsandgases.

Theintermoleculardistanceisleastincaseofsolids.Thereisnotmuchspacebetweenthemolecules.Hence,moleculesdonothavemuchfreedomtomove.Theymerelyvibrateintheirownposition.Therefore,moleculeshaveleastkineticenergy.

Theintermoleculardistanceishigherinliquidsthaninsolids.Themoleculesofmatterinliquidstatehavemorefreedomtomoveabout.Theycanmovewithintheliquidquitefreely.Therefore,moleculesinaliquidhavehigherkineticenergythanthoseofsolids.

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The intermolecular distance is highest in gaseous state. Themolecules have more kinetic energy than in liquids or solids.Inotherwordsmoleculesinasolidareclosetoeachotherthattheyhardlymove.Incaseofliquidsmoleculesmove,butdonotgetseparatedfromeachother.Theyhavefreedomtomovewithintheboundary.Ingases,moleculesareliterallydetachedfromeachother.Gasmoleculesdonothaveaspecificboundarytomoveabout.

Duetothismoleculararrangementsolidshaveadefiniteshape.Whereasliquidstaketheshapeofthecontainer.Gasesdonothaveanyshape.Solidscanbeheaped.Liquidsandgasescannotbeheaped.

Do this : Putadropofinkonthewoodentableandalsointoabeakercontainingwater.Whatdoyouobserve?Whatinferencecanbedrawn?

Howdomoleculesinagasmove?Letusexplorethisbyanactivity.

Activity 16.6

Light an agarbathi in any corner of the room. You can smell its fragrance in the whole room. How is this possible? Molecules are freely suspended in case of gases. This helps the molecules to get dispersed to all corners of the room. Gasesdonothavedefiniteshapebuttheycanbecompressed.Thispropertyofgascompressionisusedinoureverydaylife.Hereisoneexample.

You might have seen the LPG cylinder at home. What is the expansion of LPG? Shake the cylinder, taking the help of elders at home. Listen to the sound carefully. You will feel that the material in the cylinder is a liquid. LPG - Liquified petroleum gas is in the liquid state in the cylinder. Why does it change to gaseous state once it comes out of the cylinder? Gases when compressed, change to liquid state. Once the pressure is released it changes into gaseous state.

Think : WhydoesLPGcontainboththetermsliquid and gas in its name?

Activity 16.7

Take three syringes of 10 ml each without needles. Fill one of the syringes with sand, the second one with water and the third with air. Hold your thumb at the mouth of the syringe. Press the piston. Which material can be compressed easily? In which of the materials molecules can be brought closer more easily?

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Drop a few cubes of ice into fruit juice. Ice cubes though being in solid state float on the surface of juice. Why is this so?

Take a beaker. Fill it with 20 mL (20 cm3) of water. Add 20 mL (20 cm3) of groundnut oil to it. What is your observation? Why does oil float on water?

Cookingoilislighterthanequalvolumeofwaterandsofloatsonit.Inotherwordsdensityofoilislessthanthedensityofwater.

Thedensityofamaterialisdefinedasitsmassperunitvolume.Thesymbolmostoftenusedfordensityist.ItisaGreekletterandispronouncedasrho.

/ .Densityvolumemass SI unit of density is kg m3

=

Note:Onemliswrittenas1ml.Thisisalsoequalto1cm3.

Activity 16.8

Take an empty injection bottle. Measure its weight using a physical balance. Now fill the bottle with water and weigh it. Note the weight of water. Empty the bottle, dry it and fill it with sand. Now note the weight of sand. Also note the weight of materials like iron filings, raw rice, kerosene. What inference can be drawn?

Take a cubical box of 1 cm length. Fill it with water. Find its weight using a physical balance. Repeat this activity taking oil, milk and other materials which are easily available. Fill in the table as shown below.

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table 16.1-to Find the density of given materials.

SlNo

Material Volumeofthecube

Weightofthematerialtakeninthebox(ing)

Densityofthematerial(ing/cm)3

1 Water 1cc 1 1

2 Milk 1cc 1.020 1.020

3 Groundnutoil 1cc 0.91 0.91

4

5

Hereisapersonwhohasgonetoashoptopurchaseanegg.Hehascarriedabottleofwateralongwithhim.Afterpurchasinganegg,thepersonpoursthewaterthatwascarriedalongwithhimintoacontainerandimmersestheegg.Theeggfloatsonthesurfaceofthewater.Theshopkeeperismadetobelievethattheeggisrotten.Isthereanysciencetrickbehindthis?Findoutandmakealistofsimpleactivitieslikethesewhichinvolvesscientificfacts.Rememberscienceistohelppeopleanduplifthumanity.Scienceshouldnotbeusedtocheatpeople.

Think : Canpurityofmaterialsbetestedbasedonitsdensity?

Take1kgrawriceinonebagand1kgpuffedriceinanotherbag.Whichofthebagsisfilledmore?Theweightisthesame,butthevolumeofthematerialstakenisdifferent.Hencedensitiesofdifferentmaterialsaredifferent.

Hereisanactivitywhichyoucandoinsciencefairsandexhibitions.Activity 16.9

Take 20 cm3 of water in a beaker and add a few drops of white water paint to it and stir well. Like wise take 20 cm3 of white kerosene in another beaker and add a few drops of saffron oil paint and stir this too. Take 20 cm3 of carbon tetrachloride in another beaker and add a few drops of green oil paint and stir this also. Now pour all the three mixtures into another 100 cm3 beaker. Close the mouth of this beaker with the help of a watch glass and shake the beaker vigorously. Keep the beaker aside for about 20 minutes. You find three different layers in the beaker. Green in the bottom, white in the middle and saffron on top. Wow ! hats off to the tricolour that has been formed by the principle of science. There is a question that needs to be answered. Why did the three mixtures not mix with each other though they were mixed vigorously?

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Theanswerissimple.Thedensitiesofwater,keroseneandcarbontetrachloridearealldifferent.Incomparisonwithwaterwhichoftheseliquidshasmoredensityandwhichofthesehasleastdensity?Herearefewliquidslikehoney,water,saturatedsaltsolution.Tryfindoutwhichofthesehaslessdensity.

Find out : Intheaboveactivitytheliquidsdonotdissolveinoneanother,whathappensiftheliquidsweretodissolveinoneanother?

table 16.2 Density of some Materials

Material Density in g / cm3

Waterat40C 1.0000

Mercury 13.6

Milk 1.026

Magnesium 1.7

Aluminium 2.7

Gold 19.3

Iron 7.8

Lead 11.3

Platinum 21.4

Uranium 18.7

Iceat00C 0.92

Air 0.001293

Carbondioxide .001977

Carbonmonoxide 0.00125

Hydrogen 0.00009

Helium 0.000178

Nitrogen 0.001251

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AsyouallknowSIunitofdensityiskg/m3.Densityofwateris1000kg/m3.Likewisedensityofmilkis1026kg/m3.NowreferringtotheabovetableexpressthedensitiesofatleastfivesubstancesinSIunits.

Know this : Sometime around 250 B.C., the Greek mathematicianArchimedeswasgiventhetaskofdeterminingwhetheragoldsmithhaddefraudedtheKing.Thekinghadprovidedagoldsmithwithgoldtomakeacrown.Thekingsuspectedthatthegoldsmithhadaddedlessvaluablesilvertothecrownandkeptsomeofthegoldforhimself.Thecrownweighedthesameasothercrownsbutduetoitsintricatedesignsitwasimpossibletomeasuretheexactvolumeofthecrowns,soitsdensitycouldnotbedetermined.ThekingchallengedArchimedestodetermineifthecrownwaspuregold.

Onedaywhileenteringabathtub,henoticedthatwaterspilledoverthesidesofthetub.Herealizedthattheamountofwaterthatspilledoutwasequalinvolumetothespacethathisbodyoccupied.Hewasawarethatagivenmassofsilverwouldoccupymorespacethananequivalentmassofgold.Archimedesfirstweighedthecrownandweighedoutanequalmassofpuregold.Thenheplacedthecrowninafullcontainerofwaterandthepuregoldinacontainerofwater.Hefoundthatmorewaterspilledoverthesidesofthetubwhenthecraftsman’scrownwassubmerged.ItturnedoutthatthegoldsmithhadbeendefraudingtheKing!LegendhasitthatArchimedeswassoexcitedabouthisdiscoverythatherannakedthrough the streets of Sicily shoutingEureka!Eureka!Which inGreekmeans“Ihavefoundit”ThisledtothediscoveryofconceptscalledDensityandSpecificgravity.

Inmilkcollectingcentresofyourvillage,thepersoninchargewillbetooconcernedtoknowwhetherthemilksuppliedbyproducersisadulterated.Heusesadevicetotestthis.Thedeviceisalactometer.Basedonthereadingsofthelactometermilkmaybeacceptedorrejected.Whatisalactometer?Itisadeviceusedtofindthespecificgravityofmilk.Whatisspecificgravity?

Specificgravityistheratioofdensityofasubstancecomparedtothedensityoffreshwaterat4°C.

Specific Gravity :Itistheratioofthedensityofthesubstancetothedensityofwaterat40C.

Specificgravity=.

tanof water at Cof subs ce

4ct

t

Referringtothetable16.2findoutthespecificgravityofatleastfivematerials.Anexampleisgivenbelow.

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Densityofwateris1000kg/m3.IfdensityofPlatinumis21400kg/m3thenitsspecificgravityis

21.4.Specificgravityisnotexpressedinanyunits.Itisjustanumericalvalueindicatingtheratio.

Find out : Adoctorhasadvisedapatienttogethisurinetestedforitsspecificgravity.Inadulthumansnormalspecificgravityvaluerangeofurineisfrom1.010to1.020.Whathappensifthevalueislessormore?Doesitindicateanyhealthproblems?

exercises:I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Theexpressionfordensityis

a.massb.mass–volumec.mass+volumed.mass÷volume

2. Theintermoleculardistanceishigherin

a.solidsb.gasesc.liquidsd.plasma

3. Oilfloatsonwaterbecause

a.densityofoilismorethanthatofwater

b.densityofwaterismorethanthatofoil

c.densitiesofwaterandoilareequal

d.Oildoesnotdissolveinwater

II. Fill in the blanks with suitable words1. Deviceusedtomeasurethepurityofmilkis_____________.

2. S.Iunitofdensityis__________________.

3. Densityofdistilledwateris______________.

III. answer the following1. Namethethreestatesinwhichmatterusuallyexists.

2. Definedensityofasubstance.

3. Whatisspecificgravity?

4. Whydoesaneggimmersedinsaturatedsaltsolutionfloat?

5. Findthedensityofasubstanceifitsmassis180ganditsvolumeis45cc.ExpresstheanswerinSIunits.

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Chapter 17OUr COLOUrFUL WOrLD

after studying this chapter students :

• distinguishbetweenregularandirregularreflections.

• statethelawsofreflection.

• representimageformationinaplanemirrorgeometrically.

• statetheusesofconcaveandconvexmirrors.

• calculatethefocallengthwhenimagedistanceandobjectdistancearegivenforaconcavemirror.

• tabulatethedataofexperimentalobservations.

• draw diagrams showing convergence and divergence of parallelraysoflightwhenincidentonconcavemirrorandconvexmirror.

• definerefraction.

• statetheeffectsofrefraction.

• explainthemeaningoftheterms

1.totalinternalreflection2.criticalangle

• explaintheeffectsoftotalinternalreflection.

• nameopticalinstrumentscontainingconvexlensandconcavelens.

• definedispersionoflight.

• illustratebyexamples,thedispersionoflightindailylife.

• givereasonsfortheformationofmirages.

Light

Lightisaformofenergy.Energyistheabilitytodowork.Canlightdoanywork?Yes,lightcandowork.Itcanactivateyoureyes.Plantscarryoutphotosynthesiswiththehelpoflightenergy,andpreparefood.Youknowthatfoodgivesusenergyforallouractivities.Lightenablesustoseetheobjectssurroundingus.Oureyessensetheobjectsbythelightreflectedbythemorwhentheobjectsemitlight.Inphotocellslightcanbechangedintoelectricalenergy.Lighthasallthecharacteristicsofenergy.

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Know this : Lightissoimportantthatmanyparentsgivethenameoflighttotheirchildren.Ex:Prakash,Roshan,Noor,Jyothi.

Do you Know ?

Manyprayersongscontainthemeaningofmovingfromdarknesstolight.Lighthasanothermeaningofknowledge.Ex:Sentenceslike“Pleaseenlightenusabouttheworkingofhumaneye”.

MajorsourceoflightistheSun.Wealsoproducelightwiththehelpofcandles,bulb,fluorescentlampsandgaslamps.

Objectswhichhavetheirownlightareselfluminous.Sunandstarsareselfluminous.Moonappearsbright.Butitdoesnothaveitsownlight.Whathappenswhenlightfallsonasurface?Itgetsreflected.Weseethemoonbythereflectedlightofthesun.

Refl ection: You are familiarwithusing ofmirrors, seeing yourimagesinnewsteelplates,tumblersorspoons.Youhaveseenmultipleimagesinahaircuttingsaloon.Youhaveseenimagesintherearviewmirrorofmotorvehicles.

Fig17.1Reflectionoflightindifferentsituations

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Fig17.2Imagesinwaterbodies[Recallpanchatantrastoryofalionwhichgetsfrightenedbyseeingitsownimage]

Youcannotseeyourimageonawall.Butyoucanseeyourimageinamirror.Inboththecasesthereisreflection.Whatisthedifference?

Regular reflection:Inaperfectlyflatsurfaceorpolishedsurfacethereisregularreflectionwhichenablestoformanimage.Inregularreflectionthepatternofincidentlightispresentinreflectedlightalso.

Irregular or diffused reflection:Objectshavingroughsurfacereflectlightinalldirections.Lightgetsscatteredandimagesarenotformed.

Anewsteelplatewhichwillbelikeamirrorbecomesroughaftermanydaysofusingandyoucannotseeyourimageclearlybecausethesurfacelosesitspolishduetothescratchesformedduringwashing.

Fig17.3Raysreflectedfromirregularorroughsurface

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Fig17.4Regularreflection

Fig17.5Experiment:Lawsofreflection

Toknowmoreaboutthepatternofreflectionletusdoanactivity.

Activity 17.1

Obtain a rectangular piece of plane mirror from a photo frame shop. We can also get such small mirrors from street vendors. Be careful about the edges of newly cut mirrors. You can fasten paper strips along the sharp edged border of the mirror. Take a cardboard and make a slit at the centre as shown in fi g. 17.5.

You can use the back of a ready made shirt box or banian box as the stand.

Keep a white sheet of paper on one side of the hollow box and pin it at the four corners. Make incisions on the box to the size of the cardboard slit and mirror and keep it on the table. Fix the mirror strip and the cardboard slit perpendicularly in the incisions made. Pass light from a torch through the opening of the cardboard slit, in an oblique manner. We can see light ray, getting refl ected after striking the mirror.

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Thelightraywhichstrikesanysurfaceiscalledtheincidentray.Theraythatcomesbackfromthesurfaceafterreflectionisknownasthereflectedray.

Think : Ifthewallsofyourroombecomeperfectlypolishedlikemirrors,what will happen? Both regular and irregular reflections have theiradvantages.

Arayoflightisanidealization(approximation).Inrealitywehaveanarrowbeamoflightwhichismadeupofseveralrays.Weusethetermrayforanarrowbeamoflight.Abeamisacollectionoflightrays.

Now carefully draw a line on the paper with the help ofa pencil to mark the position of the mirror, the incident rayand the reflected ray. Remove the mirror, comb and torch.Draw perpendicular line to the mirror at the point where theincidentraystrikes themirror.This line iscalled thenormal to thereflectingsurfaceatthatpoint.

Fig17.6Lawsofreflection

table 17.1

Sl.No.

Angleofincidence(∠i) Angleofreflection(∠r)

1.

2.

3.4.5.

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Theanglebetweenthenormalandtheincidentrayiscalledtheangleofincidence(∠i).Theanglebetweenthenormalandthereflectedrayisknownastheangleofreflection(∠r).Measuretheangleofincidenceandtheangleofreflection.Repeattheactivityseveraltimesbychangingtheangleofincidence.Tabulatethemeasurements.

Comparetheangleofincidenceandangleofreflection.

Whatisyourconclusion?

Whathappensifalightrayisincidentalongthelineofnormal?

Activity 17.2

In the activity of 17.1, insert a scale below the white paper in the path of reflected ray slightly to raise that part of the reflected ray. The reflected ray does not appear in the raised plane or part. This means incident ray and reflected ray lie on the same plane.

Laws of reflection:

•Angleofincidenceisequaltotheangleofreflection. •Theincidentray,thenormaldrawntothemirroratthepointof

incidenceandthereflectedrayalllieonthesameplane.

Laws of reflection are valid for all types of surfaces.Howisimageformedinaplanemirror?Whatwillbeitsnature?

Asourceof light ‘O’ isplacedinfrontofaplanemirrorPQ.Two raysOAandOCareincidentonit.

Rememberingthelawsofreflectiondrawthedirectionofthereflected rays.

Drawnormals to the surface of themirror PQ, at the points AandC.ThendrawthereflectedraysABandCDatthepointsAandC respectively. Extend them further. Do theymeet? Extend thembackwards.Dotheymeetnow?Markthispointas‘I’.

Foraviewer’seyeat‘E’thereflectedraysappeartocomefromthepoint‘I’.ThereflectedraysappeartomeetatI.Itisavirtualimageandcannotbecaughtonascreen.The image isalso laterally inverted.Thatmeansleftoftheobjectwillbecomerightoftheimageandrightoftheobjectwillbecomeleftoftheimage.Theimageonaplanemirroriserectanditisasfarbehindthemirrorastheobjectisinfrontofit.In irregular reflection though the lawsof reflectionare followed, thereflectedraysarescatteredandimageisnotformed.

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LateralInversion

Fig17.7Imageformationinaplanemirror

Do this : Intheoldmethodofprinting,orthelettersonarubberletterheadseal, thealphabetswillbe latterly inverted.Holda rubberseal infrontofamirrorandfindout.

Think : Virtual imagescannotbecaughtonascreen.Thenhowis thevirtualimageformedbyamirrorcaughtontheretinaofoureyes?

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Know this : InthestoryofMahabharata,ArjunawasabletoaimattheeyeofthetoyfishbylookingatitsimageintheoilandwontheMatsyaYanthracompetition.Washeawareoflateralinversion?

Do you know ?

YoumighthaveheardaboutwhisperinggalleryofGolgumbazwhereoriginalsoundisreflectedseventimes.Thisiscalled‘echo’.RollingThunderisalsooneeffectofmultiplereflectionofsound.

Echo of light or multiple refl ections :Multipleimagesareveryfamiliartothepeoplewhovisithairdressers

shop.Youhavestudied inearlierclassesaboutmultiple reflections.RecallyourexperienceofconstructingaKaleidoscopeorPeriscope,inyourpreviousclasses.Refl ection in a curved mirror:

Youmighthaveseenmanycurvedreflectingsurfaces.Mainlytherearetwotypesofcurvedsurfaces,concaveandconvex.

Anewstainlesssteelspoonwillbeenoughtoseethepatternofimages.

Fig17.8Fig17.9Reflectioninastainlesssteelspoon

Holdthespoonasinthefigure17.8infrontofyourface.Youseeyourimage.Holdthespoonatdifferentdistancesfromyourface.Whatisyourobservation?

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Holdthespoonasinthefig17.9infrontofyourface.Youseeyourimage.Whatisyourobservation?

Spherical Mirrors: Sphericalmirrorisapartofaspherewithpolishedsurfaceononeofthesides.Therearetwotypesofsphericalmirrorsconcavemirrorandconvexmirror.

ConcavemirrorConvexmirrorThepointofconvergenceis`F’

Fig17.10Sphericalmirrors

Sphericalmirrorsalsoobeythelawsofreflection.Eachpartofthesphericalmirrorcanbeconsideredasstripsofsmallplanemirrors.Activity 17.3

Repeat the activity 17.1. This time insert a concave mirror first and after removing it insert convex mirror in the incision made for plane mirror. In place of the slit place a comb such that only 4 to 5 teeth of the comb are exposed to torch light. This can be done by covering the rest of the comb by a piece of black paper. Observe the pattern of reflected rays.

Fig17.11Fig17.12Reflectioninconcavemirror Reflectioninconvexmirror

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Concavemirrorsareusedbydentistsand insolar furnace,andinheadlightsofmotorvehicles.Convexmirrorsareusedasrearviewmirrorsinautomobiles.

Know this : Convexmirrorsalwaysproducediminishedvirtual imagesof an object. The principal focus ‘F’ of a convexmirror lies behind thereflectingsurfaceontheprincipalaxis.(fig:17.10)

Mouthmirrorusedbydentists

EnlargedviewofvehicleheadlightSolarfurnaceFig17.13Usesofcurvedmirror

Image formation in a concave mirrorYouneedtoknowthefollowingtermstostudythenatureofthe

imageformedbyaconcavemirror. 1.pole of the mirror:usuallythepoleofthemirrorislocatedat

themidpointofthecurvedsurfaceofthemirror.Therayoflight alongtheprincipalaxiswhichisincidentonthepoleofthemirror retracesitspath,alongtheprincipalaxis.Itisthecentreofthe reflectingsurface.

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2.principal focus:Itisthepointofconvergenceofaparallelbeam of lightwhich isalsoparallel toprincipalaxis,after reflection fromthemirror.Lightfromadistantsourcesuchassunraysaresourcesofparallelbeamoflight.Itisdenotedas`F’.

3.Focal length:Thedistancebetweenthepoleofthemirrorand the point of focus of reflected parallel rays of lightwhich are incidentonthemirroriscalledfocallength.Itisdenotedby‘f’.

4.Centre ofcurvature: Itisthecentreofthesphereofwhichthe mirrorisapartitisdenotedbytheletter‘C’

5. radius of the curvature:Theradiusofthesphereofwhichthemirror isapartiscalledradiusofcurvature.Itisdenotedby‘r’.Radius ofcurvaturewillbetwicethefocallength.r=2f.

6.principal axis: Theimaginaryextendedlineonwhichthepoleof themirror,thepointoffocusandthecentreofthecurvatureare located,iscalledprincipleaxis.

7.Object distance:Thedistanceoftheobjectfromthepoleofthe mirroriscalledobjectdistance.Itisdenotedby‘u’.

8. Image distance: Thedistancebetweenthemirrorandtheimage iscalledimagedistance.Itisdenotedby‘v’.

Experiment: To know the nature and position of the image formed by a concave mirror. You need a lighted candle as the object and a mirror stand and a screen.

Fig17.14Imageformationinaconcavemirror

Keepthecandleinfrontofthemirroratdifferentplacesontheprincipleaxisandadjustthescreenbymovingittoandfrotogetaclearimageofthecandleonthescreen.

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Finding the approximate focal length of a concave mirror

First find out approximate focal length by focusing a source ofparallelbeamoflight.MarkthepositionasF.Atadistanceof2ffromthemirrormarktheradiusofcurvatureofthemirroras’C’.Keepthecandleon theprincipleaxisat the followingplacesandrecordyourobservations.

1.BetweenPoleofthemirrorandF2. AtF3. BetweenFandC

4. OnC

5. Beyond‘C’

record your observations in the table

table 17.2

Position and distance of the object

Position and distance of the image

Nature of the image (Inverted or diminished or same size or enlarged)

1.BeyondC,........cm

Youhavetoadjustthescreenbetween‘F’and‘C’.......cm

2.AtC.......cm

Youhavetoadjustthescreenneartheobject......cm

3.Between‘C’and‘F’...cm

YouhavetoadjustthescreenbeyondC......cm

4.At‘F’ Youwillnotgettheimage,why?

5.BetweenthemirrorandF

Youwillnotgettheimageonthescreen.Youwillnotbeabletomeasurethedistanceoftheimage,why?Butyoucanseeitsvirtualimageonthemirror.

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Fromtheaboveexperimentcanyouanswerthefollowing?

1. Whereshouldtheobjectbeplacedtogetadiminishedimageoftheobjectonthescreen?

2. Whereshouldtheobjectbeplacedtogetaenlargedimageoftheobjectonthescreen?

3.Whereshouldthecandlebeplacedtogetaparallelbeamoflight?

Fromthetable,ifthefocallengthis‘f’,imagedistanceisv,objectdistanceis‘u’youwillnoticethat

f u vor f

v uuv1 1 1= + =+

tan tantan tan

or focal lengthSum of image dis ce and object dis ce

product of image dis ce and object dis ce=

Refraction: You have studied about opaque and transparentsubstances.

Glass and clear water are familiar examples of transparentsubstances.

Whathappenswhena ray of light passes fromone transparentmediumtoanothertransparentmedium?

Recallyourexperiences.1.Thebottomofawatertankappearstoberaised.2.Pencilpartiallyimmersedinanobliquemannerinwater

appearstobebent.3.Acoininacupwhichisjustinvisiblecanbemadevisibleby

pouringwaterinthecup.

Fig17.15Refractionoflightrays

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Thebendingoflightwhenitpassesfromonetransparentmediumtoanotheriscalledrefraction.

Likelawsofreflection,isthereanyrelationshipbetweentheangleofincidenceandtheangleofrefraction?

ABisnormalatthepointofincidence,Oispointofincidence,MOisincidentrayandONisrefractedray.

Waterisadensermediumthanair,whenanobliquerayoflighttravels from rarermedium to densermedium it bends towards thenormal.Thatmeansangleof incidencewillbegreater thanangleofrefraction.

ImagineNOasincidentrayandOMasrefractedray(seefig17.15).Thenwecansaythatwhenlightpassesfromdensermediumtorarermediumitbendsawayfromthenormal.Thatmeansangleofincidencewillbesmallerthantheangleofrefraction.

Activity 17.4

Preparation of Refraction bottle:

Fig17.16PreparationofRefractionbottle

Obtain a flat bottle, like used perfume bottles or honey bottles. Such other clear plastic bottles can also be used. Cover the bottle with brown paper, cutting out a circular piece on one of its flat side. Follow the diagram.

Pour water until half of this circular opening is filled up. Add two drops of milk to water. Through a small opening at the top corner, pass powerful beam of torch light. A key chain laser torch can also be used. When you use laser torch be careful about it. Avoid direct contact of laser light with the eyes.

Compare angle of incidence and angle of refraction, using a thin stick as normal at the point of incidence.

Anothereffectof refractionof light is illustrated in the followingfigure.Twinklingofstarsisduetothiseffect.

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Fig.17.17Thebeamsoflightdeviatefromtheirpathduetorefraction.

Total Internal reflection: If youobservecarefullyanaquariumwhichcontainsalightsourceatthebottomoftheaquarium,youmayprobablyobservetheeffectoftotalinternalreflection.

ImagineraysoflightOA,OB,OCandODfromadensermediumstrikingwatersurfaceatA,B,C,andDrespectively.AA1/,BB1/,CC1/arerefractedrays.ButDD1isreflectedray.Thisiscalledtotalinternalreflection.

Fig.17.18TotalInternalreflection

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The angle of incidence (∠OCN) forwhich angle of refraction is900(∠MCC1) iscalledcriticalangle.Rememberthatfortotal internalreflectionsthefollowingconditionsarenecessary.

1.Lightrayshouldpassfromdensermediumtorarermedium.

2.Theangleofincidencemustbelargerthanthecriticalangle.

Effects of total internal reflectionMirages : Peopleinhotdryareausuallyobservethisfrequently.Deserttravellerssometimesseetheimageofpalmtreesunderitasifthereiswaternearthetree.

Fig17.19Mirage

Intheabovediagramwhichpartoftheairthatislowerorupperisararermedium?

Miragelikeeffectcanalsobeseenonveryhotdaywhichgivesanillusionofpoolofwateratthefarendofthesightwecanseetheillusionontheupperpartofahotplatealso.Lightfromthesunisbentbythehotairneartheearth.Thesparklingofdiamondisalsoaneffectoftotalinternalreflectionoflight.

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Optic fibresYouhavestudiedthatlighttravelsinastraightlinebutyoucan

makeittravelasyouwish.Youmighthaveobservedthedecorativeopticfibreswhicharesoldintoyshopsandfancystores.

Fig17.20Decorativeopticfibres

Youmighthavecomeacrossthewordendoscopyinthemedicalfield.Withthisinstrumentdoctorscanreallyseetheinsideofyourstomach.Thisinstrumentconsistsofopticfibres.How does an optic fibre work?

Todayweareusingopticfibresinsteadoftraditionalmetallicwiresforlayingtelephonecables.Howdoesitwork?

Theprincipleistotalinternalreflectionoflight.Amagnifieddiagramofanopticfibreisgivenbelow.

Fig17.21Totalinternalreflectioninopticfibres

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refraction of light through curved transparent medium

Activity 17.5

Take a glass plate; place a drop of clear water on it. Observe the letters of a newspaper through the water drop. The letters appear big.

Activity 17.6

Take a glass tumbler with clean water in it. Dip your finger and ask your friend to observe the finger from the side of the tumbler. The finger appears big.

Likecurvedmirrorstherearecurvedtransparentmedia.

Lenses : Anycurvedpieceoftransparentmediumiscalledalens.Theyarepartofasphericaltransparentmedium.Theycanbecurvedononesideorboththesides.Theyareusefulforbendinglightinspecialways.

Fig17.22Fig17.23Fig17.24

EffectofaconvexlensEffectofaconcavelensEffectofaconvexlens

TherearetwotypesoflensesconvexandconcaveSeethefig17.23and17.24.

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Activity 17.7

Use a card board readymade shirt box like the one used to study the laws of refl ection using a comb and torch. You can perform the following experiment to know that convex lens converges the light rays and concave lens diverges the light rays.

Fig17.25Lightrayspassingthroughconvexandconcavelens

Like concavemirrors we can use convex lens to get inverted,diminishedorenlargedimagesofanobjectwhichcanbecaughtonascreen.

Concavelensneverformsrealimages.Theyformdiminishedimagesofobjects.Thisisusefulinviewfinderofcameraswherewecanseelargeareainsmallspace.

Commonly used thingswhich contain lenses are given in thefollowingdiagram.

Fig17.26Thingswhichcontainlenses

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Doyouhaveaconvexlenswithyou?

Yes youdohave.Your eyes contain convex lens.Howdoes thislenshelpustosee?Thislensisnotmadeofglassbutasoftjellylikesubstance.

Dispersion of light : Youare familiarwithmost spectacular eventrainbow. You have seen rainbow like colours in soap bubbles, infountains,andcompactdiscofcomputerdevices.Sometransparentplastic ball points,whichhave hexagonal or octagonal shapes alsoproducerainbowlikecolours.

Fig17.27Dispersionoflight

White light ismadeup of ranges of colours ofwhich seven arenotseeninaseparatedpattern.Thesplittingupofwhitelightintoitsconstituentcoloursiscalleddispersion.Intherainbowyoumaynotseeallthesevencolours.Itisduetooverlappingofcolours.

Withthehelpofanarrowbeamoflight,glassprismandarrangementoflensesitispossibletoproducethebandofsevencoloursusingwhitelight.Thisbandiscalledspectrum.Therearemanytypesofspectrum.

Itisnotnecessarythatthesourceoflightshouldalwaysbewhitetogetaspectrum.Compositelightwhichcontainsarangeof3to4coloursalsoproducesabandof3to4colours.Aglowing40Wtungstenfilamentbulbdoesnotproducepurewhitelight.Itisasourceofcompositelight.Itwillalsoproduceaspectrumbutthespectrummaynotbethesameasthespectrumofwhitelight.Thetypeofspectrumdependsuponthenatureofsourceoflight.

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Activity 17.9

produce a band of colours:

Immerse a plane mirror in an

Fig17.28Splittingofwhitelight

inclined osition in a bowl containing water. Let the reflecting surface be partially or fully be immersed in water as shown in the figure. Allow sun rays to fall on the reflecting surface of the mirror immersed in water. Catch the reflected rays on a screen of white paper. You will see band of colours like rain bow. You will study more about lenses and dispersion of light in higher classes.

exercises :

I. Four altertnatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Rearviewmirrorofmotorvehiclescontain

a.planemirror b.convexmirror

c.concavemirror d.convexlens

2. Ifarayoflightistravellingfromdensermediumtorarermediumandiftheangleofincidenceisgreaterthancriticalangle,thenthefollowingtakesplace

a.reflection b.refraction

c.dispersion d.multiplerefraction

3. Aconcavemirrorformsmagnifiedinvertedimagewhentheobjectisplacedat

a.‘F’b.‘C’c.between‘F’and‘C’d.beyond‘C’

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4. Onanewstainlesssteelspoonifyouseetheimageofyourfaceupsidedown,thenthatpartofthespoonactslike,

a.convexlens b.concavemirror

c.convexmirror d.concavelens

5. Youcanseetheimageofyourfaceonthesurfaceofstillwater.Butifthewaterisdisturbedyourimagewillnotbeclear,becauseof

a.totalinternalreflection b.refraction

c.irregularreflection d.dispersion

II. Fill in the blanks with suitable words :

1. Theletter“P”lookslike__________________inaplanemirror.

2. Watchrepairersusethelensofthetype__________________.

3. Bendingoflightwhenitpassesfromonetransparentmediumtoanotheriscalled________________________.

4. Formationofrainbowisdueto_______________________.

III. answer the following:

1. Giveonereasontoprovethatlightisaformofenergy.

2. Whatisthedifferencebetweenregularandirregularreflection?

3. Statethelawsofreflection.

4. Mentiontheusesofconcavemirrors.

5. Whyisconvexmirrorusedasrearviewmirrorinmotorvehicles?

6. Mentionanytwoeffectsofrefractionoflightindailylife.

7. Whataretheconditionsfortotalinternalreflectiontotakeplace?

8. Writediagramstoshowtherefractionofparallelraysoflightin(i)convexlensand(ii)concavelens.

9. Mentionanyfourdevicesthatcontainconvexlens.

10. Drawraydiagramsofconvergenceanddivergenceoflightraysinaconvexandconcavelens.

11.Whatisdispersionoflight?

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IV. Match the following:1. dispersion a.planemirror

2. diminishedimage b.concavelens

3. enlargedimage c.mirage

4. totalinternalreflection d.convexmirror

e.rainbow

f.multiplereflections

g.glassslab

extended learning activities. preparation of multipurpose beam box

Fig17.29Beambox

Youneedthehelpofacarpenterforthis.Arectangularshoeboxtypewoodenboxandphoto frame cardboardswith thewhitepaperpastedonitarerequired.Alsoa40to60wattbulbandbulbholder,acombareneeded.Thediagram17.29willmakeitclear.

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Chapter 18

FOOD aND ItS CONStItUeNtS after studying this chapter students :

• describetheimportanceoffood.

• listthemajorconstituentsoffood.

• statetheimportanceofeachofthemajorconstituentsoffood.

• classifythefoodintovariousgroupsbasedonitspredominantconstituents.

• giveexamplesforfoodrichincarbohydrates,fatsandproteins.

• describetheimportanceofroughagesandwaterinourfood.

• conductsimpleteststodetectthemajorconstituentspresentincommonlyknownfooditems.

• appreciatetheimportanceofbalanceddiet.

Allorganismsrequirenumberofthingstosurvive,growandremainactive.Theyincludeair,waterandfood.Noorganismcansurviveforlongwithoutfood.Oneoftheseveralthingsthatarecommontoalllivingbeingsisthattheyallneedfoodtosurvive,remainhealthyandtocarryoutvariousactivities.Humansarenoexceptiontothis.Howlongcanapersonsurvivewithoutfood?Notlong!

Food becomes your blood and bones, brain andmuscles. Foodbecomesyoursizeandstrength,energyandstamina.Foodcontributestoyourphysique,effectivenessandemotionalstability.

Weknowsomuchabout food.What is foodthen?Wetake foodthroughthemouth.Canwecalleverythingthatweconsumethroughourmouthasfood?Whentakeninthroughthemouth,itshoulddigesteasily andprovide thenecessarymaterials and energy to the body.Further,itshouldnotcauseharmtothebody.

Think : Are there any items in your viewwhicharenot foodalthoughtheymayprovideenergytoourbody?

Waterdoesnotprovideanynutrients.Howeverwaterishighlyessentialtoourbody.Canweconsiderwateraspartofourfood?Ourbodyrequiresiron.Canironnailsbeapartourfood?

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General Functions of foodEvery living organism including humans needs energy. Energy

enablesustomove,grow,andreproduce.Isthistheonlypurposeoffood?Thepurposesoffoodaremainlythreefold.Foodpromotesgrowth,suppliesenergyandfurnishesmaterialsfortherepairofbodyparts.Everybreath,everythought,everymovement,wearsoutsomeportionofourbody.Variousvitalprocessesremovethewornanduselessparticles.Thebodycompensatesfortheselossesbyconstantrenewedsupplyofmaterialsthroughfoodanddrink.

Fig18.1Variousfunctionsoffood

Our body has to carry outmany functions.Different functionsrequiredifferentmaterials.Evenifwegetenoughfoodtofillourstomach,wecanbeunhealthy.Thisisbecausewedonotgetallessentialelementsfromjustonetypeoffood.Hence,weneedtoeatdifferentkindsoffoodtogetallofthethingsweneedforthebody.

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Activity 18.1

Is there variety in the food you eat? What are the various types of food items normally used in your home? Do all families use the same types of food? Find out. What factors determine the type of food we eat?

Find out : What happens, if we do not get any or adequate food?Discuss the problems that arise out of hunger. Hunger is not gettingenoughof the rightkinds of food tomeet ourneeds.All countries andregions have atleast some people who are hungry. Is it fair? Does itnot reflect that we are living in an unequal society? What are yourviews on this?Discuss how the people in theworld canwork togetherso that everyone will have enough and the right kinds of food to eat.

Constituents of food: Foodcontainsnourishingsubstancescallednutrients.Nutrientsaretheultimatenourishingchemicalsfoundinfood.Theykeepourbodyfitandactive.Differentkindsoffoodcontaindifferentthingsessentialtoourbody.Thefoodmayalsocontainconstituentsthatdonotsupplyanynutrients.Thesenon-nourishingmaterialsarehoweveressentialtoourbody.Hence,theyshouldformanintegralpartofourfood.Theyincludefibresandwater.

Fig18.2Majorconstituentsoffood

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Scientistshaveidentifiedmanynutrientsinourfood.Eachofthesehasspecificfunctions.Therearethreemajornutrients.Theseareenergygivingnutrients,protectivenutrientsandbodybuildingnutrients.Youhavestudied inyourearlierclassesabout thesenutrients.Knowingaboutnutrients,theirsourcesandfunctionsaddspurposetooureatinghabits.Further,ithelpsustochoosethekindsoffoodweeat.

energy giving food

Allouractivitiesrequireenergy.Ourbodyneedsenergyevenwhenwearesleeping.Ourenergysupplycomesfromtwomajorsources.Ourmajorsourcesofenergyarecereals,sugar,jaggery,somekindsoffruitsandpotatoes.Thesefoodscontainlargequantityofchemicalscalledcarbohydrates.Thesearethecompoundsmadeofcarbon,hydrogenandoxygen.Wealsogetenergyfromtheoils,butterandghee.Manyofthenutsandmeatalsocontainfairquantityofoilsandfats.Wesometimesrefertooilsandfatsas lipids.Theyserveasconcentratedenergyfood.

Fig18.3Somefooditemsrichincarbohydrates

Carbohydrates ondigestion turn into glucose.Glucose gets intotheblood.Thebloodsuppliesglucosetoeachlivingcellsofthebody.Any inadequacy or excess of glucosemight lead to adverse effects.Insufficientsupplyofglucosemayleadtotiredness,weaknessandlackofconcentration.Excessofglucosecanaddtoourweight.Hence,wemusttakecarbohydratesinmoderatequantity.

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Carbohydrates help in the regulation of sugar in the bloodstream.Thisensuresadequatesupplyofcarbohydratestoeverycell.Thus, carbohydrates act as a shield and protectmuscles.Complexcarbohydratessuchascelluloseareexcellentsourceoffibre.Fruits,dairyproducts,jaggery,sugarandvegetablesprovidesimplecarbohydrates.

Activity 18.2

Figure 18.3 shows some sources of carbohydrates. Observe the figure and make a list of food items rich in carbohydrates.

personwithintenseandactivelifestyleneedsmorecarbohydrates.Unusedcarbohydratesinthebodyarestoredupasfats.Personswithsedentarylifestylemustbecareful.Excessivecollectionoffatsinthebodymayresultinoverweightandobesity.Thismayinturnleadtomanyotherhealthproblems.

Think: Athletesandsportspeopleafteran intenseactivityeatglucose.Howdoesthishelp?Whichisbetterinsuchsituations:glucosecommonsugarorbakedpotatoes?Whydoyouthinkso?

Asyoualreadyknowcarbohydratesandlipidssupplyenergytoourbody,whoneedshigheramountofcarbohydratesintheirdiet?

The functions of carbohydrates aremultiple. Therefore, it isnecessarytoincludefooditemswithcarbohydratesinourmeal.Forinstantenergygeneration,sugarsandstarchareperfectfuels.Theyhelptocarryoutphysicalactivitiesefficientlyandeffectively.Fibrespresentin carbohydrates such as cellulose keeps bowelmovement smooth.Consumptionofcarbohydratesindifferentfoodswillalsopavewayforconsumptionofotheressentialnutrients.Therefore,itisnecessarytogoinforvarietyofcarbohydratefoodsources.Carbohydratesaddtothetasteandappearanceoffood.Thismakesthedishtemptingandmouth-watering.Weusesomeofthemassweeteners.Therefore,wemusteatfoodrichincarbohydrates.However,itisbettertogoinfornaturalslowdigestingcarbohydrateslikevegetables,fruits,nuts,legumesandwholegrains.

Functions and principal sources of lipids

Lipidsconsistofmoleculesmadeofcarbon,hydrogenandoxygen.Theyareinsolubleinwater.Thereareseveraltypesoflipidsincludingoilsandfats.

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Lipidsplayaveryimportantroleinourbody.Theyhelpinbrainfunctions, smoothmovement of joints, clotting of blood and energyproduction.Different lipids do different things. For instance, somelipidshelptobringdowninflammationwithinthebodyandlubricatethejoints.Ourbodymakessomelipidsandwegetsomefromourdiet.

Fig18.4Somefooditemsrichinlipids

FathelpsthebodytoabsorbandtomovethevitaminsA,D,E,andKthroughthebloodstream.Ourbodywouldlackinthesevitaminsintheabsenceoflipids.Cellmembranescontainlipids.Theylubricatethecells.Thelubricationservesasaprotectivebarrier,whichcontrolsthemovementofmaterials.Lipidsstoreenergyandhencehelpinenergyproduction.However,excesslipidsmaycauseweightgainandobesity.Regularexerciseandphysicalactivitycancontroltheproblem.Lipidsalsoactasmessengerswithinourbody.Fatsalsohelp tomaintainhealthyskinandhair.Thus,lipidsaremostessentialtolife.

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Think : Oilsandfatsinourdietisnottheenemybutourlifestyleis!

Mostlipidsofplantoriginareintheformofoils.Thesearerelativelyhealthier.Most fats, on theotherhand, come fromanimal sources.Theyarenotgoodforhealth.Doctorsusuallydonotrecommendbutter,cheese,wholemilk,icecream,cream,fattymeats,coconutandpalmforsomepeople.

Functions and principal sources of proteinsProteinsareveryimportantmoleculesinourcells.Theyareinvolved

inallcellfunctions.Therearevarietiesofproteins.However,allproteinsweconsumearetypicallyconstructedfromasetdrawnfrom20simplecompounds called amino acids.Most amino acidmolecules includeatomsofcarbon(C),hydrogen(H),acarboxylgroup(-COOH)andanaminogroup(-NH2].

Eachofthedietaryproteinhasaspecificstructure.Thestructuredetermines the function of proteins in our body. Someproteins areinvolvedinstructuralsupport.Someotherproteinsareinvolvedinbodilymovement.Yetothersassistinbuildingupdefenceagainstgerms.Youmighthaveheardofenzymes.Theyarealsoprotiens.Theseproteins

Fig18.5Somefooditemsrichinproteins

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facilitatebiochemicalreactionsinsideourbody.Forexample,thereisanenzymecalledpepsin.Itplaysanimportantroleindigestion.Itworksinthestomachtobreakdownproteinsinfood.Similarly,thereisanotherenzymecalledlactase.Itbreaksdownthesugarpresentinmilk.Severalofthehormonesinourbodyareproteins.Theyaremessengerproteins.Forexample,insulinhelpsinthemetabolismofcarbohydrates.Itisonesuchmessengerprotein.Youmusthaveheardofhaemoglobin.Thisproteinispresentinourblood.Itplaysacrucialroleinthetransportofoxygeninourbody.Someproteinslikekeratinandcollagenarefibrousand tough. They provide support to tendons and ligaments. For alltheseactivitiesandmore,ourbodyrequiresaminoacids.Someofthesemustbepresentindiet,asourbodycannotsynthesizethem.

Wemustplanourdiettogettheessentialaminoacids.Combiningvarietyofrightfoodtogetherinonemealwillgiveadequateproteintoourbody.Thebodyusestheseproteinsformaintaininghealthygrowth.

Activity 18.3

What are the foods rich in proteins? Look for information on this or consult a doctor. What are the major foods that give proteins to your body? Make a list of them. What else can you do to improve your protein intake?

Functions and principal sources of vitamins and minerals

Vitamins andminerals are required in smaller quantities formaintaining health. Vitamins are essentially compounds of carbon.Thereareseveralwell-recognizedvitamins.SomeofthemlikevitaminCandvitaminBarewater-soluble.OtherslikevitaminA,D,KandEarefat-soluble.Wealsoneedcertainsubstanceslikebeta-caroteneandfolicacid,whichgetconvertedintovitaminsinourbody.Wecallsuchsubstancespro-vitamins.Forexample,beta-carotenegetsconvertedinto vitaminA in our body. All of these vitamins and pro-vitaminspromoteourhealth.Table18.1givesvariousvitamins,theirfunctionsandtheirsources:

Think : Doesyourdietprovideyouwithallthevitamins?Doyouknowofpeoplewhoaresufferingfromailmentsofonekindortheotherduetovitamindeficiency?Findout.

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table 18.1: Some vitamins, their functions and sources

Vitamin Some Major Functions Some Natural Sources

A Promotesskeletalgrowth,normaltoothstructure,healthyskin,eyesandnightvision.

Fishliveroils,liver,carrots,green,pappayaandyellowvegetables,dairyproducts.

B1 Helpsconvertsugarandstarchesintoenergy;promotesdigestion,strenthenheartmuscle,promotesgrowth;preventsfatigue

Wholewheat,driedyeast,oatmeal,peanuts,pork,prawn,sunflowerseeds,soyabeansprouts.

B2 Helpsinreleasingenergytobodycells;enablesutilizationoffats,proteinsandsugars.

Dairyproducts,liver,kidney,yeast,leafygreens,fish,eggs.

B3 Helpstomaintainahealthydigestivetractandnervoussystem.Inverylargedoses,lowerscholesterol

Mushrooms,prawn,Tuna,Chicken,Beef,Peanuts,enrichedGrains.

B6 Involvedinaminoacidmetabolism,preventscertainskindisorders,retardedgrowthandconvulsions

Cerealgrains,yeast,liver,milk,wheatgerm,meat,beef,bananas,milk,eggs.

B12 Promotesutilizationofprotein,fatsandcarbohydrates;essentialforformationofredbloodcells;buildsnucleicacid;preventsanaemia;helpsnervoussystem.

Liver,beef,pork,eggs,dairyproducts,shellfish.

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C Neededforabsorptionofiron,someproteinsandfolicacid;preventsoxidationofothervitamins;stopsinternalbleeding;strengthensbloodvesselsmaintainshardbonesandteeth;promotesstamina;holdsbodycellstogetherpreventsinfections,colds,fatigueandstress;healswoundsandburns.

Citrusfruits,berries,greenandleafyvegetables,tomatoes,cauliflower,amla,orange

D Promotesboneandtoothdevelopmentandnormalgrowth;helpsutilizationofphosphorusandcalcium;maintainsnervoussystemandheartaction;preventsrickets.

EggYolk,Milk,ExposuretothesunenablesbodytomakeitsownVitaminD

E Protectsbody’sstoreofVitaminA,strengthenscapillarywalls;regulatesmenstrualrhythm;preventslossofothervitamins;helpsbloodflowtoheart;lowersbloodcholesterolandfattyacids;vitaltocellhealth;regulatesproteinandcalciummetabolism

Soyabeans,vegetableoils,sprouts,leafygreens,enrichedflour,wholewheat,wheatgerm,wholegraincereals,eggs.

K Helpsinclottingofblood,assistsinthesynthesisofproteins

GreenVegetables,Liver,eggyolk;alsomadebyintestinalbacteria.

Minerals in our diet:Ourdietshouldessentiallycontainseveralmineralsincludingcalcium,iron,copper,magnesium,zincandiodine.Eachofthesemineralsplayvariousrolesinthefunctioningofourbody.Forinstance,calciumhelpstobuildbonesandteeth;helpsintheproperfunctioningofmuscles,heartandnerves;relievespainandcramps;helpsinclottingofblood.Dairyproducts,soyabeans,Ragi,sunflowerseedsandlegumesarerichincalcium.

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Ironisanotherimportantmineral.Itisaconstituentofhaemoglobin,whichplaysanimportantroleinoxygentransport.Liver,meat,oysters,oatmeal,nuts,beans,wheatgermandgreenscontainiron.

Iodinehelpsinthefunctioningofthyroidgland.Itpreventsgoitre.Ithelpstoburnfat;convertsbeta-carotine intovitaminA;regulatesenergyproductioninourbodyandmaintainshair,nail,skinandteeth.Seafoodsandvegetablesareagoodsourceofiodine.

Zincinourdietwillhelptoreducecholesteroldeposits;helpsinthemakingofenzymesandinsulin;supportsmetabolismofcarbohydrates;facilitatestheproperfunctioningofprostategland.Eggs,cheese,beef,pork,wheatgerm,brewer’syeastandpumpkinseedsaresomeofthegoodsourcesofzinc.

Potassiumisamineralthathelpstoregulatefluidbalanceinourbody.Wealsoneeditfortheproperfunctioningofnervesandmuscles.peanuts,bananas,greenbeans,mushroomsandorangesareafewgoodsourcesofpotassium.

Activity 18.4

What other minerals are essential to our body? Find out the sources and functions of each of those minerals. Represent the data collected in a suitable table.

Functions and principal sources of roughagesRoughagefoodsarefoods,whichhavehighfibrecontent.Theycome

indifferentforms.Thefoods,whicharerichindietaryfibre,arefruits,vegetablesandgreens.Thesearealsogoodsourceofvitamins,mineralsandotherusefulsubstances.Wholegrainsalsoprovideroughage.Almostallvegetablesareexcellentsourcesofroughage.Dietaryfibreisimportantbecauseitprovidesvolumetothefood.Thisfacilitateseasymovementofmaterialsinthealimentarycanal.Wavelikemuscularmovementsofthewallsofthedigestivetractbringaboutthemovementofmaterials.Whenthematerialshavelittlebulk,themovementofmaterialsinthelargeintestineandbowelmovementbecomesdifficult.Thisisbecausetoomuchofwaterisabsorbedfromtheundigestedfood.Hence,thematerialsbecomerelativelydryandhard.Thisresultsinconstipation.Peopleoftensaytheyhavetheproblemof‘constipation’.Topreventthis,itisimportanttoincreasethevolumeoftheintestinalcontent.Wecanachievethisbyincreasingtheroughageinourdiet.

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History of dietary fibres:Theword ‘Fibre’ gainedcurrency in1970s.ThiswasduetoDr.DenisBurkitt.Hemadeahypothesisthatdietaryfibrecanpreventcertaindiseases.HeandhiscolleaguesmadeastudyondietarycontentsinAfrica.TheydiscoveredthatAfricansdidnotsufferfromcertaindiseasesthatarecommoninWesterncultures.For example, diabetes, high blood pressure, obesity, gallstones,intestinalproblems,coloncanceretcwereararityinAfricancultures.Theyattributedthistohighintakeofdietaryfibreandlowintakeofrefinedcarbohydrates.Theyalsonotedtheemergenceofsuchdiseasesinthewestafter1890.Thisfollowedtheintroductionofanewmillingtechniquethatremovedfibrefromwholegrainflour.RightfullyDr.DenisBurkittwasnicknamedasthe‘Fibreman’.

Activity 18.5 Make a list of foods you eat that are rich in fibres.

Functions of water in our body : Thehumanbodycanlastweekswithoutfoodbutnotwithoutwater.Waterconstitutesabout55–75percentofourbodymass.Theprominentconstituentofblood,digestivejuices,urineandperspirationiswater.Waterisessentialforthehu-manbody.Thebodycannotstorewaterandmusthavefreshsupplieseverydaytofacilitatemetabolicprocesses.Wealsoneedfreshsuppliesofwatertomakeupforlossesfromlungs,skin,urineandfaeces.Theamountweneeddependsonourmetabolism,theweather,thefoodweeatandouractivitylevels.

Waterhelpstomaintainthehealthofeverycellinthebody.Itkeepsthebloodthinenoughtoflowthroughbloodvessels.Ithelpstoeliminatethewastes and excessmaterials.Water regulatesbody temperaturethroughsweating.Itkeepsmucousmembranes,lungsandmouthinmoist conditions.Water helps digestion and prevents constipation.Itimprovesthetextureoftheskinanditsappearance.Ithelpstocarrynutrientsandoxygentothecells.Itservesasashockabsorberinsidetheeyes,spinalcordandintheamnioticsacsurroundingthefoetusinpregnancy.Ifyoudonotdrinkenoughwaterregularly,thereissomeincreasedriskofkidneystones,dehydration,urinarytractinfectionsinwomen.Babiesandeldersarevulnerabletodehydration.Howcanweavoidthis?Onemustincreasewaterintake.Symptomsofdehydrationincludeheadaches,lethargy,dryorcrackedlips,dark-colouredurineandphysicalweakness.Eventuallyurination stops, thekidneys failandthebodycannotremovetoxicwasteproducts.Inextremecases,thismayresultindeath.Diarrhoea,vomiting,orbotharethecommoncausesofdehydration.

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Whatshouldonedoincaseapersonisshowingsymptomsofdehydration?You must have heard of OralRehydration Solution. People callthisinshortasOrS.Itisasolutionofcommonsaltandsugarinpotablewater.PrescriptionsfromtheancientIndianphysicianSushrutadatebackover 2500 yearswith treatment of

acute diarrhoeawith ricewater, coconut juice, and carrot soup.However,thisknowledgedidnotcarryovertotheWesternworld.Manypeoplethere,diedduetodehydrationuntilthe“Oral rehydrationtherapy”,becamepopular.Inthelate1950s,Dr. hemendra Nath Chatterjee inIndiaprescribedORSforcholerapatientsandachievedgoodresults.

Activity 18.6

You can prepare ORS at home. Take one litre of potable water in a clean vessel. Add one teaspoonful table salt and six teaspoonfuls of common sugar. Give this in plenty to a person with dehydration. Ready packets of ORS prepared as per the guidelines of WHO are available in market. They may contain glucose, potassium chloride and trisodium citrate.

Think : Anintakeof6-8glassesofwateradayisrecommended.However,somepeopleeitherdonotdrinkwaterordrinkinverysmallquantities.How can they survive? What are the other ways of feeding the bodywithwater?Makealist.

tests for major constituents of foodNowyoumaybecurious toknowtheprincipalnutrientpresent

inaparticularfooditem.Therearesomesimpleteststodiscoverthenutrientinagivenfood.Youdonotrequirebigorcostlyequipmentstodothis.Trythesetestsanddiscoverforyourself.Takethehelpofyourfriends,teachersoradults.Simple tests for carbohydrates

test for glucose:Asyouknow,glucoseisasimplecarbohydrate.Totestthepresenceofglucose,youneedasolutioncalledBenedict’sreagent.Itisabluesolutionofcoppersulphate,sodiumhydroxide,andtartaricacid.Itisavailableinachemist’sshop.Youalsoneedaspiritlampandatesttubeholder.

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Dissolveapinchof glucose inabout5mlwater taken ina testtube.Addabout5-6dropsofBenedict’sreagentandheatforabouttwominutes.Notethechangeincolourifany.Appearanceofabrickredprecipitateindicatesthepresenceofglucose.Whydoyougetthebrickredprecipitate?

test for starch:Starchisacomplexcarbohydrate.Totestforthepresence of starch, youneed iodine solution. This is available in achemist’sshop.Takeasmallquantityofthegivenfoodstuffinadish.Add2-3dropsofiodinesolution.Notethecolourchangeifany.Theappearanceofablue-blackcolourindicatesthepresenceofstarch.Simple test for proteins

Biuret test - for proteins: YouneedareagentcalledBiuretsolutiontoconductthistest.Itisabluishsolutioncontainingsodiumhydroxideandasmallamountofcoppersulphate.

Takeabout5mlofthesolutioninatesttube.Add5-6dropsofBiuretsolution.Waitforawhile.Donotheat.Acolourchangefrombluetopinkindicatesthepresenceofproteinmatterinthesolution.Simple test for lipids

emulsion test for fats and oils: Emulsion is amixture of twoliquidswhichdonotmixwithoneanother.Itisasuspensionofoneliquidinanother.Takeafewgroundnutseeds.Crushitwellandtakeitinatesttube.Addasmallamountofethylalcoholtoit.Shakewell.Heatthetesttubecarefullyonawaterbath.Donotdirectlyheatonaflamebecausealcoholisflammable.Whenthesubstancedissolvesinalcohol,filterordiluteuntilyouobtainaclearliquid.

Takeasmallquantityoftapwaterinanothertesttube.Pourthesolutionpreparedabove,gently,intothetesttube.Awhitishsuspensionindicatesthepresenceoffatoroil.

Wehavestudiedinthischaptermanyaspectsoffood.Abalancedhealthydietisonethatprovidesallthenutrientstoourbodyinrightproportions.Weallneedadaily intakeofavarietyofnutrients likecarbohydrates,proteins,fats,vitamins,minerals,anddietaryfibretomaintainnormalhealth.Weneedthesenutrientsinvaryingproportions.Takingbalancedfoodwillpreventmanydiseasesandkeepourbodyhealthyandactive.Youwillstudymoreaboutfoodnutrientsinhigherclasses.

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exercises :

I. Four altertnatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Themajorcompoundpresentinthebonesisthefollowingmetala.sodium b.iron c.calcium d.phosphorus

2. Childrenliketoeatbakeryitemsandchocolates.Eldersadvisethemtoeatvegetablesalso,andnottokeepasidecurryleaveswhileeatingfooditems.Thisshowstheimportanceof

a.carbohydratesb.dietaryfibresc.proteinsd.lipids

3. Agreenleafthathasfallendownfromaplantistakenandiskeptinwaterforsometimeandthentakenout;Itisthendippedinspiritand iodine solution. The leaf turns bluish indicating thepresenceof

a.starch b.oil c.protein d.fibre.II. Fill in the blanks with Suitable words :

1. Emulsiontestisconductedtodetect______________________.

2. FatsolublevitaminsareA,D,Eand______________________.

3. Aminoacidscontaintheelementscarbon,hydrogen,oxygenand______________________.

4. ThemicronutrientthatisresponsiblefortransportationofOxygentothedifferentpartsofthebodycontainsthemetal______________.

5. Biuretsolutioncontainssodiumhydroxideand__________________.

III. Match the following :

A B 1.Haemoglobin a.nightblindness

2.VitaminC b.clottingofblood

3.VitaminA c.developsteeth

4.VitaminK d.oxygencarrier

e.developsbones

f.improvesimmunitysystem

g.developsmuscles

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IV. answer the following :

1. Whyshouldwehavevarietyinourdiet?

2. Listfourmajorsourcesofcarbohydratestothepeopleinyourregion.

3. What food itemsused inyourregiongive lipidstothepeoplewhoconsumethem?

4. Listthenutritionalimportanceofproteins.

5. Whydosomepeoplesufferfromnutritionaldeficienciesdespitehavingenoughfood?

6. Explaintheimportanceofwaterinourdiet.

7. Abeakercontainsathickliquid.Howdoyoutestwhetheritisalipid?

8. Whatisthefunctionofcalciuminourbody?

9. Whyiswateressentialtoourbody?

10.Listall themajorclassesof ingredients thatshouldbepresent inbalanceddiet.

11.Makealistoffooditemsthatarerichindietaryfibres.

think :

1. Whydoyoungchildrenboth inrichandpoor familiessuffer fromnutritionaldeficiencies?Whatareyoursuggestionstoimprovethesituation?

2. How does lack of nutrition affect your activities, studies andpersonality?Howcanyouhelpyourself?

3. Whatdietarychangesinyourhomewillimprovethenutritionalstatusofyourfamilymembers?

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Chapter 19

DIGESTIon anD RESpIRaTIonafter studying the chapter students :

• definelifeprocess

• experimentallyprovethatcarbondioxideisrequiredforphotosynthesis

• appreciatetheroleofphotosynthesisinbringingaboutbiodiversity

• differentiatebetweenlightanddarkreactions

• prepareatransversesectionofleaf

• usemicroscopetoviewspecimen

• analysetheimportanceofbeinghygenic

• makeacomparativestudybetweendigestivesystemofcockroachandhumans

• comparerespirationincockroachandhumanbeings

Youhaveseenmanytypesoflivingthingsaroundyou,fromtinyinsectstobulkytreesandanimals.Iftheselivingthingsaretosurvivethentherearemanylifeactivitiesthathavetotakeplaceinthem.Plantsand animals look so different yet theyhave certain life activities incommon.Theyarerespiration,nutrition,growth,movement,responsetostimuli,excretionandreproduction.Thesearecalledlifeprocesses.Thereareseverallifeprocessesthatkeepthemalive.Nowinthischapterletusstudytwooftheselifeprocessesnutritionandrespiration.

All organisms require food.Why is food essential?Where doorganismsgetfoodfrom?Youhavealreadylearntthatsomeorganismscanprepare their own food. Such organisms are called autotrophs.Allgreenplantsareautotrophs.Greenplantspreparetheirfoodbyaprocesscalledphotosynthesis.

Activity 19.1

Sow a few bean / ragi seeds in two separate boxes. Allow the seeds to germinate. Shift one of the boxes which contains plants to a dark room, and the other box to a well lit and ventilated room. Observe the plants in the boxes after about 48 hours. What is your conclusion?

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Know this : MeaningofPhotosynthesis

Photo=Light,Synthesis=Preparingorputtingtogether

Atthetimeoforiginoflife,theearthhadmoreofcarbondioxide.Graduallyalgaeandprimitiveplantsstartedappearing.Thesealgaeandtheotherlowerplantsutilizedthiscarbondioxidetopreparefood,andinturngavebackoxygentoatmosphere.Thus,levelofoxygenincreasedintheEarth’satmospherewhichisalsoareasonfornewerkindsoflifeformstoemergeonearth.

Photosynthesis isachemicalreaction.Like, inanyof theotherchemicalreactions,therewillbereactantsandproductsinphotosynthesisalso.Reactantsmayalsobeconsideredasrawmaterials.Whataretherawmaterialsrequiredforphotosynthesis?Letusexplorethiswiththehelpofthefollowingexperiment.

experimenttoshowthatcarbondioxideisnecessaryforphotosynthsis.Taketwopottedplantswhicharekeptinadarkroomfortwodays.Mark one of the pots as ‘A’ and the other as ‘B’. Place a beakercontainingPotassiumhydroxidesolutionnexttoplant‘A’andabeakercontainingsodiumbicarbonatesolutionnexttoplant‘B’.Coverboththepotsseparatelybybell jarsorpolythenebagsasshown in thefigure19.1.Takeprecautionssuchthatairdoesnotenterthepolythenebags.Placeboththepottedplantssidebysideinawelllitroomforabout48hours.Testafewleavesofboththeplantsforstarch.Whatinferencewillyoudraw?Note : Takethehelpofyourteacherfortestingtheleavesforstarch.

Fig19.1Experimenttoshowthatcarbondioxideisnecessaryforphotosynthesis

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Think : Whyshouldthepottedplantsbekeptinadarkroomforabout48hoursbeforebeginningtheexperiment?

Whatistheroleofpotassiumhydroxideandsodiumbicarbonate?

Fromtheaboveexperimentyoumayhavecometotheconclusionthatcarbondioxideisrequiredforplantstopreparefoodintheformofstarch.Iscarbondioxidetheonlyrawmaterialusedbytheplantsforphotosynthesis?No,theyalsorequirewater.

Think: Anushaiswalkinginagardennexttoabusymainroad.Shecollectsafewleavesfromaplantnexttothemainroad.Sheobservesadustylayeronthesurfaceoftheleaves.Willthedustylayerpresentonthesurfaceofleaf,affectfoodproduction?

You have already learnt that roots absorb water andmineralnutrientsfromsoil.Howdoescarbondioxideentertheplantbody?Weshallfindtheanswerbyconductingthefollowingactivity.

Activity 19.2

Cut a thin section of Nerium leaf along the mid rib. Place the section in a petridish containing water. Place this leaf section on a microscope slide. Add a drop of water and cover the specimen with the help of a cover slip. Observe the minute openings on the surface of the leaf.

Fig19.2LeafsurfaceshowingstomataAsinglestomataenlarged

Theminuteopeningswhichyouhaveobservedarecalledstomata.Carbondioxideenterstheplantbodythroughstomata.

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Fig19.3Sectionthroughtheleaf

Apartfromstarch,oxygenisalsoaproductofphotosynthesis.Letusexaminethiswiththehelpofthefollowingexperiment.

experiment to Show that oxygen is released during photosynthesis.

Taketwotroughsfilledwithwater.Addafewcrystalsofsodiumbicarbonatetoboth.PlaceHydrillaplants inboththetroughsandinvertlargefunnelsoverthem.Taketwotesttubes.Placesmallpiecesofsteelwool into theirbottoms.Fill the test tubeswithwaterandinvertthemoverthenarrowendsofeachofthefunnel.Placeoneofthetroughsinabrightsunnyareawhereastheothertroughinadarkcupboardforabout48hours.

Testthegascollectedinthetesttubesbyintroducingsplinters.Whatisyourinference?

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Fig19.4Experimenttoshowthatoxygenisliberatedduringphotosynthesis

Asstatedearlier,photosynthesisisachemicalreaction.Itcanberepresentedwiththehelpofanequation.

Carbondioxide+waterChlorophyll

Sunlight starch+oxygen+water

6CO2+12H2OChlorophyll

Sunlight C6H12O6+6O2+6H2O

Wheredoesphotosynthesistakeplaceinleaves?Alreadyyouhavelearntaboutanorganellecalledchloroplast.Photosynthesistakesplaceinthechloroplast.

Forbetterunderstandingofphotosyntheticprocess,itisimportanttorecallthestructureofachloroplast.Asyouareallawaretherearetwomajorregionscalledgranaandstromainthechloroplast.ThesetworegionsareinvolvedintwodifferentphasesofphotosynthesiscalledLightDependentreactionwhichisalsocalledLight reaction. Light Independent reaction isalsocalledDark reaction.

Fig19.5Structureofchloroplast

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Light dependent reaction: Light dependent reaction takes place in the presence of sunlight, in the grana region. During this reaction water is decomposed into hydroxyl and hydrogen ions by the help of light energy. Oxygen is given out by plants in this phase. Light energy is converted to chemical energy and is stored in the form of ATP. What is the use of Chemical energy that has been released during light reaction? This energy is used to prepare starch during light independent reaction.

Light Independent Reaction: In this reaction carbon dioxide is reduced to starch, utilizing the energy released during light dependent reaction. This reaction takes place in the stroma region.

Note : Many times it is wrongly believed that light independent reaction takes place only during night times.

By now you are able to differentiate between the two phases of photosynthesis. What if sun would not have been present? Plants could not have chloroplast. Soil did not contain all essential nutrients required for plants growth.

You might have heard of a famous saying ‘struggle for existence’. Will plants survive in the absence of these factors? If not all, some plants can survive fighting some of the odds.

When soil is poor in nitrogen, plants try to obtain nitrogen by other means. Here is a group of photosynthetic plants which obtain nitrogen by trapping and digesting insects. Such plants are called insectivorous plants. Example – Drosera, Nepenthes.

Fig 19.6 Nepenthes Fig 19.7 Drosera

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Think : Canothercommonplantsgrowinareaswherelotsofinsectivorousplantsgrow?

Youmighthaveseensomeplantsgrowingontrees.Theseplantscapableofphotosynthesistakeshelterinthehosttree.Suchplantsarecalledepiphytes.Example–Orchids.

Fig19.8Orchids

Think : Howdoorchidsabsorbwater?

Cananimalsprepare theirown food?Notonlyanimals,bacteriaandfungialsocannotpreparetheirfood.Theseorganismsarecalledheterotrophs.Theirmodeofnutritioniscalledheterotrophicnutrition.

Youmight have seen compost heaps in your village. Compostobtainedbythedecompositionoforganicmatterisanexcellentnutrientsupplement toagriculturalfields.Howdoes thisdecompositiontakeplace?Thankstofungiandbacteriawhichfeedonorganicmatterbydecomposingthesame.Hencebacteriaandfungiarecalledsaprophytes.

Think : Areallbacteriaandfungisaprophytic?

Letusdoanactivity.Takeafewslicesofbread.Sprinkleafewdropsofwateronthem.Keepthemasidefortwodays.Youwillfindaspongymaterialappearingontheslicesofbread.Observethesespongymaterialsunderacompoundmicroscope.

Sometimesyoumighthaveseenblackishorgrayishspongymaterialontheinnersurfaceofbrokencoconut.Observethemunderacompoundmicroscope.Thesearefungi.Howdofungiderivenutrition?

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BreadmouldRhizopusAgaricus

Fig19.9Commonexamplesoffungi

Fungiderivetheirnutritionfromdeadanddecayingorganicmatter.

Think : Whatwouldhappeniftherewerenosaprophytes?

Willmouldsgrowonslicesofbreadkeptinarefrigerator?

Haveyoueverbeenadviseddewormingbyadoctor?Youmighthaveheardorseenwormsbeingeliminatedinthefaeces.Whereweretheseworms?Fromwherewouldthesewormsgetnutrition?Weretheyofanyusetohostpersonsinwhomtheywerefound?

Thesewormswere in the intestine. Theyhad taken shelter andnutritionfromthehost.Buttheyareofnousetothehost.Suchwormsarecalledparasites.Manytimestheyarefoundtobeharmfulandfatalalso.

Find out : Areheadliceparasites?Howcanwegetridoftheirmenace?Youcanpreventthesebypropertreatmentandalsobybeinghygienic.

Itwouldhavebeensoniceiftheorganismsthattakeshelterandnutritionfromushadbeenhelpfultous.Thenwecouldhaveappliedthestatement‘afriendinneedisafriendindeed’toorganismsalso.Notallorganismsareourenemies;therearemutuallybeneficialorganismstoo.YoumighthaveheardofbacteriacalledE.coli presentinourintestine.Whatwoudhappeniftheywerenotpresent?ThenweshouldhavebeentakingB-Complextabletsandinjectionsregularly.TheseE.colibacteriatakeshelterandnutritionfromusandinreturnprovideusthevitalB-Complexvitamins.Herebothhumansandthebacteriaaremutuallybenefited.ThemodeofnutritionobservedinE.colibacteriaiscalledmutualism.Thisisalsocalledsymbiosis.

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Find out : Is mutualism found in plants?

Is there a symbiotic relation between insects and plants?

Heterotrophic Nutrition

You are already familiar that animals are heterotrophs. The type of nutrition found in animals is called holozoic. Holozoic nutrition involves five steps.

a. ingestion ingestion → digestion → egestionb. digestion ↓ c. absorption absorptiond. assimilation ↓e. egestion assimilation

Animals take in food by a process called ingestion. The food that enters the animal’s body should be broken into simple usable forms; this is done by a process called digestion. Food can be reduced to simple usable forms mechanically and by using certain chemicals. Mechanically food is crushed by teeth. Chemically food is digested with the help of digestive enzymes. Digested food is directly taken into the cytoplasm in lower animals such as amoeba. In higher animals such as human beings digested food is absorbed and transported to cells and tissues through blood. This process is called absorption. Digested food is stored or utilized in the cells. This happens by a process called assimilation. The undigested food particles are eliminated from the animal body by a process called egestion.

You know that there are different types of animals. Is nutrition and digestion similar in all animals? Let us find out by taking the examples of amoeba, cockroach and human being.

As you are aware amoeba is unicellular. All life activities have to take place in the same cell. Amoeba feeds on bacteria, diatoms, unicellular algae, minute protozoa and even dead organic matter. Hence, it is an omnivore.

How does amoeba move? Can the same locomotory structures be used to take the food into its cell? Observe the following diagram, look how the pseudopodium is surrounding the prey and ingesting. Should a live prey not be killed before being ingested? If yes, should the pseudopodia contain special substances to perform this task?

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Activity 19.3

Refer science books and encyclopedias in your school library and find out how pseudopodia is specialized to trap and kill the prey.

Fig19.10Nutritioninamoeba.

The ingestedpreyenters the foodvacuolewheredigestion takesplace.Digestiveenzymessuchasamylaseandproteasearesecretedinthefoodvacuole.Amylasedigestscomplexcarbohydratesintosimplesugars.Proteasedigestsproteinstoitssimplestforms.Digestedfoodis diffused into the cytoplasm from the food vacuole. Cytoplasm iscirculated through out the cell so that all parts of the cell receivenutrients.Digestedfoodisusedforallitslifeactivities.Undigestedfoodisegestedwiththehelpofpseudopodia.

Raju’sgraphsheetsareeatenawaybycockroaches.Hismotherisworriedastomatoesaredrilledandeatenbycockroaches.Hewondersastohowacockroachcaneatanddigestanything?Inordertofindthesolutiontohiscuriosityhecollectsafewcockroachesandplacestheminatransparentplasticbox.Heplacesvarietiesofmaterialslikerubber,pencilpiece,piecesofpaper,coconutpiece,pieceofclothandgreenchillies.Cockroachfeedsonalmosteverything!

Rajuobservestheexternalfeaturesofacockroachusingamagnifyinglens.Youmayalsodothis.Youcanidentifythreemainregionscalledthehead, thoraxandabdomen.Lookat thefigure19.11;observeapairoffeelersintheheadregion.Thesearealsocalledtheantennae.Antennaesensethefoodandmaypushthefoodintothemouth.Foodiscrushedinthemouth.

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Fig19.11Cockroach

Think : Doall insects feed just like the cockroach?Discusswith yourteacherandfriends.Observeananteatingitsfood.Itisreallyinteresting.

Find out : Themouthpartsofthecockroach’swhichhelpincrushingthefood.

Raju has a lotmore curious questions regarding digestion incockroach.He decides to collect information from various sources.Hemakesalistofhisobservations.

Fig19.12Digestivesystemofcockroach

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table 19.1: Cockroach digestive system : parts and functions

part of the alimentary

canal

Function enzymes secreted

Function of the enzyme

Foregut•mouth•oesophagus• crop•gizzard

Foodiscrushedandlubricated.Foodpipe,allowsfoodmovement.Foodisstoredforashortwhile.Actsasgrindingchamber.

Salivaryamylase

---

------

Maltose

---

------

Midgut

• stomach

• haemocoel

(bodycavityfilledwithblood)

Storageoffood,majorsiteof

chemicaldigestion.

Digestedfoodisabsorbedthroughthestomachwallsintothesurroundingspacecalledhaemocoel.

a.Storesdigestedfood

b.Digestedfoodistransportedfromhaemocoeltovariouspartsofthebody.

a.amylase

b.maltase

c.invertase

d.tryptase

e.lipase

---

Amylaseconvertsstarchintomaltose

Maltaseconvertsmaltoseintoglucose

Invertaseconvertssucrosetoglucose

Tryptasehelpsinthedigestionofproteins.

Lipasehelpsinthedigestionoflipids.

---

hindgut•rectum

•anus

Reabsorptionofwaterfromfaeces.

Faecalpelletsareexcreted.

---

---

---

---

Rajuhasadoubtastowhatwastheneedforwatertobereabsorbedfromthefaecesinthehindgutofcockroach.Tryhelptohimtofindtheanswer.

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Letusnowlearnhowdigestionprocessoccursinhumanalimentarycanal.Humandigestivesystemismuchmorecomplexthanthedigestivesystemofcockroach.

alimentary CanalAlimentary canal is also calleddigestive tract. It is thepathway

bywhich food enters the body and solidwastes are expelled. Thealimentarycanalincludesthemouth,pharynx,esophagus,stomach,smallintestine,largeintestineandanus.

Think : Arehumanbeingsomnivores?Whydohumanbeingsprefereatingcookedfood?Whatmayhappenifweconsumeonlyrawfood?

Theingestedfoodissubjectedtomechanicalbreakdowninmouth.Foodischewedandchurnedwiththehelpofteethandtongue.Salivamakes food into a soft paste called bolus. Saliva contains salivaryamylasewhichconvertsstarchintomaltose.

Fig19.13Humandigestivesystem

activity : Chew about 10 grains of pounded rice(CªÀ®QÌ) for 10minutes.Howdoesittaste?Why?

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Do you know ?

Anadulthumanbeingsecretesabout1–1.5litresofsalivaperday.

Boluswhenswallowedentersthepharynx.Pharynxisthecommonpassageforbothfoodandair.Bolusentersfoodpipewhichisalsocalledoesophagus.Atissuecalledepiglottispreventsbolusfromenteringintothewindpipe.

Think : Whatmayhappenifthereisanaccidentalentryoffoodintowindpipe?

Whydowegethiccups?

Know this : Hereisapersoneatinghisfood,whiletalking.Heisnotawareoftherisk.Guideandeducatehimsothathecomesoutofthisbadhabit.

Theboluspassesthroughtheoesophagusandreachesthestomach.Thishappensbytherhythmiccontractionofthemusclesthatmaketheoesophagus.Ittakesaround7to9secondsforthebolustoreachthestomach.Oesophagusisanarrowmusculartubeoflength20–30cm.

Think : Oesophagushasnoroleindigestion.Why?

Fig19.14Peristalisis

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Boluswhichentersthestomachisstoredforsometime.Stomachsecretesgastricjuicewhichcontainshydrochloricacid.Thishydrochloricacidcommonlykillsthemicrobesthatmayhaveenteredthroughfoodandwater.Whatmayhappeniftoomuchofacidissecreted?Isthereanyotherusefromtheacidsecretion?Digestiveenzymessuchaspepsinandrenninarealsosecretedinthestomach.Pepsinconvertsproteinsintopolypeptides.Renninconvertssolublemilkproteinsintoinsolublecurds. At this stage, bolus in the stomach turns into a semi liquidstatecalled‘chyme’.Chymeentersthesmallintestine,wheredigestioncontinuesfurther.

Bilejuice,pancreaticjuiceandIntestinaljuiceactuponchymeanddigestitfurther.Bilejuiceisproducedbytheliverandisstoredinthegallbladder.Pancreaticjuiceisproducedinthepancreaswhereasintestinaljuiceisproducedintheintestine.Bilejuiceemulsifiesfats.Pancreaticjuicecontainsproteaseamylaseandlipaseenzymes.Amylaseconvertsstarch intomaltose,whereas lipase converts complex fats to simplefats.Intestinaljuicecontainsmaltase,sucrase,lactase,peptidaseandlipase.Maltaseconvertsmaltosetoglucose.Sucraseconvertssucrosetoglucose.Lactaseconvertslactosetoglucoseandpeptidaseconvertspolypeptidestoaminoacids.Digestedfoodisabsorbedbythefingerlikeprojectionsofthesmallintestinecalledvilli.Thisdigestedfoodiscirculatedtoallpartsofthebodywiththehelpofcirculatorysystem.Youwillbelearningregardingcirculatorysysteminyourlaterclasses.

Undigested food is passed on to the large intestine. There isreabsorptionofwaterfromthefaecesinthelargeintestine.Faecesiseliminatedthroughtheanus.

Find out : Hereisanurbanpersonwhoalwayseatslotsofpizzasandburgers.Thispersonisexperiencingdifficultyinpassingoutfaeces.Whatsuggestionwouldyouliketogivethispersontoovercomethisproblem?Listoutotherdigestivedisordersandalsosuggestremediestoovercomethosedisorders.

Note : Referchapter18inyoursciencetextbook.Youmaygetsomeideastohelphimovercomethisproblem.

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respiration

Youknowthatenergyisrequiredtodowork.Wheredowegetenergyfrom?Inwhatformwillthatenergybepresent?Theanswersforthesequestionscanbelearntwiththehelpofthefollowingexample.

After having completed a 400m running race, an athlete feelsfatigue. She is given one or two spoonful of glucose powder. Afterhavingconsumedglucosesheregainsenergy.Thisimpliesthatenergyis releasedwith the help of glucose. Youmay recall that complexcarbohydrates,getconvertedtoglucoseindigestionprocess.

Glucoseonreachingthecellsreactswithoxygentoliberateenergy.Thisprocessiscalledrespiration.

Insomeorganismsenergycanbereleasedintheabsenceofoxygen.Likephotosynthesisrespirationisalsoachemicalreaction.Thereleaseofenergyfromfoodmayormaynotutilizeoxygen.Ifoxygenisused,tobreakthefoodforenergyliberationthenitiscalled‘Aerobicrespiration’.Elseitiscalled‘anaerobicrespiration’.Theycanberepresentedwiththehelpofequations.

aerobic respiration Glucose+Oxygen→Carbondioxide+Water+Energy

C6H12O6+6O2→6CO2+6H2O+Energy

anaerobic respiration Glucose→EthylAlcohol+Carbondioxide+Energy

C6H12O6→2C2H5OH+2CO2+Energy

YouhaveheardofProkaryotes,theydonotcontainmitochondria.Thenhowisenergyreleasedinthem?Energyliberatedduringanaerobicrespirationislessthantheenergyliberatedduringaerobicrespiration.

Letuslearntheprocessofrespirationinamoeba,cockroachandhumanbeings.

Respirationinamoebatakesplacebydiffusionthroughbodysurface.Cockroachbeingabitmorecomplexcontainsaseparaterespiratorysystemcalledtrachealsystem.

Thetrachealsystemincludes

Spirades of trachea and tracheoles

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Fig19.15Respiratorysystemofcockroach

Stigmata are respiratory openings incockroach. There are ten pairs ofstigmatawhicharealsocalledspiracles.Of these ten stigmata, two pairs arepresent in thoracic region and eightpairsareintheabdominalregion.Thesespiraclesarepresentonthelateralsideofthebody.

Tracheaandtracheolescarryoxygenfrom the diffused air to all the partsof the body. Cells take in oxygen bydiffusionandgiveoutcarbondioxidetothetracheole.Haemolymph, thebloodof cockroach, is involved in gaseousexchange between the cells. Carbondioxideisdiffusedoutofthecockroach’sbodythroughthespiracleopenings.

Standinfrontofamirror,

Fig19.16Humanrespiratorysystem

observe the chestmovementsasyoutakeinandgiveoutair.Takinginandgivingoutairiscalled breathing. How isbreathingrelatedtorespiration?

Webreatheinandbreatheoutairwiththehelpofrespiratorysystem. Respiratory systemconsists of nose, pharynx,trachea, bronchi and lungs.Lungsincludebronchiolesandalveoli. Observe figure 19.16and recognize the respiratoryparts.

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Fig19.17Humanlungs:-internalstracture

Airentersthenasalcavitythroughthenostrils.Dustparticlespresentinthisairarepreventedfromreachingthelungs.

Think : Whatspecialstructuresofnasalcavitypreventthedustparticlespresentintheinhaledair?

Apersoninadustyplaceoftensneezes.Why?

Whyshouldtheinhaledairbewarmedupinthenostrils?

Isitsafetobreatheinairthroughmouth?

Airpassestothepharynxfromwhereitisdirectedintothetracheawith thehelp of epiglottis. Trachea contains ‘C’ shaped ringswhichpreventitfromcollapsing.Tracheaisdividedintotwobranchescalledthebronchi.One bronchus enters the left lungwhereas the otherbronchusenters theright lung.Thesebronchiare furtherbranchedintobronchioles.Airsacsarepresentattheterminalsofbronchioles.Thesearecalledalveoli.

Bloodcirculatingaroundthealveoligivesoutcarbondioxideandcollectsoxygen.Oxygenatedbloodreachesthecellsandgivesoxygentothecells.Thisoxygenisusedforoxidizingglucose.Inthisprocesscarbondioxideformedasaproductiscarriedbybloodtothealveoli.Thisairisexhaledinthesamepathway.

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Know this : “Whenthebreathwanders,themindisunsteady,butwhenthebreathisstill,soisthemindstill.”- hatha Yoga pradipika

Youmust haveheard of a practice in yoga called Pranayama.Breathingislife.Itisoneofourmostvitalfunctions.OneoftheFivePrinciplesofYogaisPranayamaorbreathingexercise,whichpromotesproperbreathing.InaYogicpointofview,properbreathingistobringmoreoxygentothebloodandtothebrain,andtocontrolPranaorthevitallifeenergy.pranayama YogaalsogoeshandinhandwiththeAsanas.TheunionofthesetwoYogicPrinciplesisconsideredasthehighest formofpurificationandself-discipline,coveringbothmindandbody.IMpOrtaNCe OF praNaYaMa

Thebrainneedsmoreoxygenthananyotherorganofourbody.If it is starved of oxygen it becomes inactive resulting inmentalsluggishness, depression, negative thoughts, impaired vision andhearing.the advantages of pranayama:

1. Controlledbreathingkeepsthebodyfitandhealthy2. Itincreaseslongevity.3. It tonesup liver, stomach, intestine, digestive system and

kindlesgastricfire.4. It strengthens thenervous system, improves concentration

andcalmsthemind.5. Iteliminatesnegativethinking.6. Itdecreasesmetabolicrate.7. Itdecreasestheheartrateanddecreasesbreathingrate.8. Itdecreasesbloodpressureandincreasesskintemperature.9. It inducesrelaxationofmindandreducesmentaltensions,

anxietiesandworries.

10.Itimprovesmemorypowerandeliminatesmentaldisorders.

here are a few interesting facts:1. Whileatrestthebodytakesinandbreathesoutabout10liters

ofairperminute.

2. Therightlungisslightlylargerthantheleftlung.

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3. Right lung has three lobes whereas the left lung has only two lobes.

4. Surface area of lungs is roughly around the size of a tennis court.

5. An adult at rest usually breathes 12 to 15 times in a minute. Here is a conversation between a doctor and a patient.

Patient: Hello doctor.

Doctor: Hello….take a seat….what is your problem?

Patient: Dear doctor…..I have come here with a few health problems….

Doctor: Yes, please go ahead….

Patient: I have cough…..I cough continuously…..

Doctor: Is it dry cough or wet cough??? Patient: Its wet cough …..There is discharge of sputum….....…

sometimes sputum is mixed with blood…..

Doctor: Do you get fever?

Patient: Yes doctor I do get fever…especially in the evenings…..I feel so fatigued now a days….and also I have lost my appetite……and also I have lost my weight…….

Doctor: Since how many days do you have these problems?

Patient: For a month doctor…..

Doctor: I suspect you have TB…..Let me confirm this through various investigations……

Patient: Oh…..this is an infection caused by Mycobacterium tuberculosis…..and this bacterium primarily infects the lungs…….pulmonary TB is a respiratory disease…..

Doctor: Oh that’s really great….you know so many facts regarding TB …… Do you know TB is curable!

Patient: Yes doctor….that’s the reason why I am not tensed…….Are you familiar with any other respiratory diseases? Make a list

of respiratory diseases you are aware of and also mention a few tips to avoid them.

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exercises:

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Theprocessofobtainingfoodandutilizingitinthebodyis

a.respiration b.nutrition c.excretiond.reproduction

2. Oneoftheseisaproductofphotosynthesis

a.starch b.glucose c.maltose d.sucrose

3. Insectivorousplantscommonlygrowinareaswheresoilisdeficientin

a.carbon b.nitrogenc.potassium d.phosphorus

4. Apersonapplieshydrogenperoxideonhiswound.Thisistokill

a.anaerobicbacteria b.aerobicbacteria

c.fungi d.protozoa

5. Amylaseconvertsstarchto

a.glucose b.sucrose c.lactose d.maltose

II. answer the following:1. Whatarelifeprocesses?

2. Explainthemethodoftestingaleafforstarch.

3. Explainanexperimenttodemonstratethatoxygenisreleasedduringphotosynthesis.

4. Differentiatebetweenthetwophasesofphotosynthesis.

5. Whatareparasites?Givetwoexamples.

6. Amoebacannotdigestfats.Why?

7. Explainrespirationincockroach.

8. Explainrespirationinhumanbeings.

9. Drawadiagramofhumandigestivesystemandlabeltheparts.

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Chapter 20

REpRoDUCTIon In HIGHER pLanTSafter studying this chapter students :

• understandtheimportanceofreproductioninplants.

• drawthediagramofatypicalflower.

• relatethestructureandfunctionsofthepartsofaflower.

• statetheimportanceofinsectsinplantreproduction.

You are aware of the fact that reproduction is one of the basiccharacteristicsoflivingorganisms.Reproductiondiffersfrommanyothercharacteristicsoflifesuchasnutritionandrespiration.Itisabsolutelynecessaryforthesurvivaloftheentirespecies,whileitisnotnecessaryforthesurvivalofanindividualorganism.

Youhave learnt in your earlier classes that there are twobasictypesofreproduction–asexualandsexual.Lowerorganismssuchasmoneransprotistans,algaeandfungigenerallyreproducebyasexualmethods.Lookattheexampleslikepotatoandsugarcane.Thestemcangiverisetonewplants.Greenplantsexhibitvegetativeandsexualreproduction.

Sexualreproductioninvolvestheformationandfusionofspecializedreproductivecellscalledgametes.

Inthischapteryouwillstudytheprocessofsexualreproductioninthemostadvancedgroupofplants–theangiosperms,commonlycalledfloweringplants.

Floweristhereproductivestructureofaplant.Flowerisapartofshootsystemmodifiedforthepurposeofreproduction.Generallytheflowersproutsfromtheaxilofaleaf,calledbract.Theflowerisgenerallyborneonastalkcalledpedicel.

Think : Arethereplants,whichdonotproduceflowers?Thenhowdotheyreproduce?

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Look at this diagram showing the parts of a typical flower.

Youcanseethatthetipofthepedicel is enlarged to form adisc shaped thalamus. In thethalamusthedifferentpartsoftheflowerarearrangedinfourconcentricwhorlsorcircles.Ifyoulookfromoutsidetoinside,these whorls are the calyx,corol la, androecium andgynoecium.

Calyx is the outermostwhorl composed of greencoloured units called sepals.Theyprotecttheinnerpartsofaflowerinthebudcondition.

Corollaisthesecondwhorlfromoutside.Itiscomposedofusuallybrightlycolouredunitscalledpetals

androeciumisthethirdwhorlfromoutside.Itiscomposedofmalereproductivestructurescalledstamens.Stamensproducepollengrains.Inthepollengrainsmalegametesareformed.

Theinnermostwhorliscalledgynoecium.Itiscomposedoffemalereproductivestructurescalledcarpels.Eachcarpelhasabasalswollenovary, amiddle elongated style and terminal sensitive region calledstigma.Ovaryenclosestheovules. In theovule femalegametes,ovaareformed

Activity 20.1

Collect a fresh hibiscus flower. Identify the stamens and the ovary. Place them in separate petridishes containing water. Split open the anthers of the stamen. Examine the anther with a hand lens. You will be able to see yellow coloured particles. These are the pollengrains. Cut open the ovary along its length. Using the hand lens observe whitish structures inside the ovary. These are the ovules.

InAngiosperms,processofsexualreproductionhastwomajoreventsnamelypollinationandfertilization.

Fig20.1Structureofatypicalflower

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Theprocessoftransferofpollengrainsfromtheanthertothestigmaiscalledpollination.Ifthepollengrainsgettransferredtothestigmaofthesameflower,itiscalledselfpollination.Ifthepollengrainsgettransferredtothestigmaofanotherflowerinanotherplantofthesamespecies,itiscalledcross-pollination.

Innaturecrosspollinationismorecommonthanselfpollination.Itisbecausecrosspollinationhasmanyadvantagestoplants.

Crosspollinationoccurswiththehelpofagentslikewind,waterandanimals.Flowersthatarepollinatedbywindaregenerallysmallanddullcoloured.Theyproducelargenumberofdryandlightpollengrains. Sugarcane,maize and grass are common examples ofwindpollinatedplants.

Inaquaticplantsgenerally,weseetheformationofseparatemaleand femaleflowers.Maleflowersdetach fromtheplant,floatonthesurface.Thefemaleflowersremainattachedtotheplant.Maleflowersarecarriedtowardsthefemaleflowersbywatercurrent,wheretheyreleasepollengrains.Valisneria,hydrillaandelodeaarecommonexamples.

Inmostplantscrosspollinationisbroughtaboutwiththehelpofinsects, likebutterflies,mothsandbees.Suchflowers showcertainmodifications to attract insects. Thesemodifications aremainlyconcernedwiththecolourofthepetals.Someflowerscontainglandscallednectarieswhichproducenectartoattractinsects,thatbringaboutcrosspollination.Flowerswhichopenduringnight,usuallyhaveadullcolouration,buthaveanaromaticsmellthatattractsinsects.

Apartfrominsects,theonlyothergroupofanimalsthatvisittheflowersarethebirds.Severalkindsofsmallerbirdsvisittheflowerforfeedingonnectarandintheprocessbringaboutcrosspollination.Therearealsoinstancesofflowersthatarepollinatedbybatsandevensnails.

The processwhich follows pollination is called fertilization. Itinvolvesthefusionofthehaploidmalegameteinthepollengrainwiththehaploidfemalegameteintheovule.

Tobringaboutfertilization,thepollengrainswhichgetdepositedonthestigmaofthecarpelmustpenetratethestyleandreachtheovule.Henceitproducesaprojectioncalledpollen tubewhichgrowsthroughthelengthofthestyleandfinallyreachestheovule.Thepollentubecontainsmalegamete.

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Activity 20.2

Take two slides containing a shallow pit. Such slides are called cavity slides. Pour a few drops of water into one slide and a few drops of 2% sucrose solution into another. Shake a slit open anther from a hibiscus flower into each of these slides. Keep the two slides in a safe place for a about 4 hours. Later examine the slides under a microscope What do you notice?

The pollen grains in the slide containing sucrose solution, show the formation of the pollen tube. What is your inference?

Inside the ovule, there is a structure calledembryo sacwhichenclosesthefemalegamete.ThepollentubereachestheembryosacThenmalegameteinpollentubeandfemalegameteinembryosacunite.Thusfertilizationtakesplaceresultingintheformationofadiploidcellcalledzygote.

It is interestingheretoknowthechangesthattakeplace intheflowerafterpollinationandfertilization.

• Thediploidzygotedevelopsintoanembryothatlaterdifferentiatesintoaseed,thatlatergrowsintoanewplant.

• Surroundingtheembryo,anutritivetissuecalledendospermisformed.

• Theentireovulenowbecomestheseed.

• Thecoveringsoftheovuletransformintotheseedcoat.

• Ovaryportionofthecarpelgetstransformedintothefruitenclosingtheseed.

• Petals,sepalsandotherpartsoftheflowerfalloff.

Thus, pollination and fertilization result in the formation ofseedwhichisenclosedinthefruit.Thisisacharactersticfeatureofangiosperms.

Youareawareofthefactthatthevarietyofvegetablesthatweuseasfood,areallpartsoftheangiospermplants.Differentpartsoftheangiospermplantsserveasourfood.Itmaybeintheformofleaves,stem,root,fruitortheseed.

Activity 20.3

•Make a list of the vegetable that are used for making food in your house.

Classify them into leaves, stems, roots, fruits and seeds.

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•Find out the vegetables used by your friends or neighbours. Did you notice some differences?

The seeds that we use as a part of staple food are generallydistinguishedintopulses,millets,cerealsandgrains.

· pulsesaretheprincipalsourcesofproteins.Ourcountryisthelargestproducerandconsumerofpulses.Theyareprimarilyseedsoccurringinvariablesizesandcoloursinsideatypeoffruitcalledpod.Allofthembelongtothepeafamily-Leguminosae.Theyinclude,blackgram,peaandlentil.

· Grainsaresmall,harddryseedswithorwithoutthefruitwallattached.Mostofthegrainsaregeneralydescribedascereals.Theyareproducedprimarilybyvarieterofgrassesbelongingto the familypoaeceae.Maize, rice,wheat, barley oats andsorghumarethecommonGrainsthataccountformorethan85%ofthetotalgrainproductionintheworld.

· Millets are coarse grainswhere the protein content is saidtobehigher.Jowar,bajra(pearlmillet)andragiarecommonexamples.Theseedsaremuchsmaller.

exercises :

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer:

1. Seeddevelopsfrom

a.ovary b.ovulec.embryod.embryosac.

2. Colourofnightbloomingflowersisusually

a.violet b.redc.yellowd.whitish.

3. Thecorrectsequenceofreproductivestagesseeninfloweringplantsis

a.gametes,zygote,embryo,seedling

b.zygote,gametes,embryo,seedling

c.seedling,embryo,zygote,gametes

d.gametes,embryo,zygote,seedling

4. Theanthercontains

a.ovulesb.femalegametes.c.diploidcells d.pollengrains.

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II. Fill in the blanks with suitable words :

1. Flowerswithbluepetals,nectarandstrongscentaremostlikelypollinatedby_______________.

2. Variationsintheoffspringisthecharacteristicof__________________reproduction.

3. Thereismuchwastageofpollengrainsin____________pollination.

4. Fertilizationleadstotheformationof________________.

III. answer the following :

1. Whatisreproduction?

2. Whatissexualreproduction?

3. Whatispollination?

4. Areinsectsfriendsoffarmers?Explain.

5. Drawthediagramofatypicalflowerandlabeltheparts.

Firm Determination : Have firm determination and strong will-pow-er to cultivate good habits in order to achieve permanent happiness, peace, success and fulfillment in life.

-Swami Vivekananda

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Chapter 21

CommuniCation gadgetsafter studying this chapter students :

. definethetermelectromagneticwave.

. definethetermslikeaudiofrequency,videofrequencyandradiofrequencywaves.

. definethetermtransducerwithrespecttomicrophone.

. givereasonformodulation.

. locatefrequenciesofradiostationsbytuningtheradioreceiversets.

. drawblockdiagramsof.a.Radiotransmitterb.Radioreceiver

. Identifysimilaritiesbetweenradioandmobilephoneswithrespecttoaudiotransmitter.

. StatetheadvantagesofInternet.

People talkabout ‘shrinking’of theworld. Is it reallyshrinking?Englandhasbecomeveryclose.DoesitmeanthatthedistancebetweenIndiaandEnglandhasdecreased?Herethemeaningisdifferent.

ItissaidthatAdilshahofBijapurhiredtheserviceofanengineerfrom Iran to build thehistoricGol-Gumbuz.Howdidhe send theinvitationtoIranfromBijapur?HowmuchtimedidtheengineertaketoreachBijapur?

MahatmaGandhijiwenttoEnglandtoattendroundtableconferencebyship.Thejourneytookmanydays.

IfsuchthingsweretohappentodayMahatmaGandhijiwouldhavereachedEnglandveryquickly.InsteadofgoingtoEnglandhewouldhavepreferredtheroundtableconferencewithWinstonChurchillthrougha“tele-conference”.

Vehicles like cars, trains, ships, aeroplanes, jets and rocketsmovethepeopleandgoodstodifferentplaces.Theyarethemeansoftransportation.Similarlywecanmoveinformation,messagesandvisualsfromplacetoplace.

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Ataboutthespeedoflightwhichis3lakhkilometrepersecond,itispossibletosendalettertoAmericaorDubai.ItispossibletoseeTendulkarhittingasixerinSouthAfricaalmostatthespeedoflightatourhome.Thisexchangeortransportationofinformationiscalledcommunication.Theremarkableprogressinthefieldofcommunicationhasshrunktheworld.Theplacesintheglobehavebecomecloserbycommunicationnetwork.

Do you know ? Birds,animalsalsoexchangeinformation.Observationoftheiractivitiesmayhelp you to infer their intention.Tribal peoplewatch thebehaviorofanimalsandhearthechirpingsoundsofbirds,whileadjustingtothenature.

Do you know ? RelaydrumbeatsasinPhantomcomic,torchlightsignalsbyseatravellers,lighthouseontheseacoastwereearlymethodsofdistantcommunication.

Know this : Famous poet Kalidasa imagined sending of messages onclouds in his work “Meghasandesha”. Pigeons were also used to sendwrittencommunication.

In this chapter we shall study the fundamentals of moderncommunicationdeviceslikeRadio,Television,Telephone,mobile,FaxandInternet.

electromagnetic waves Youhavecometoknowabouttheinterestingaspectsoflightinthe

previousclassesandalsointhisclass.

Lightasyouhavestudied,isjustapartofbroadelectromagneticspectrum.YouknowaboutvisiblespectrumVIBGYOR.

Thisbandofsevencoloursisvisibletooureyesbuttherearelightwaveswhicharenotvisibletous.AboveRed,beyondvioletalsotherearewaves.

For example: Right in yourroom,therearewavesofAkashvani,Bangalore.Youcannotseethem.Butyoucandetectthemusingaradio.

Electromagnetic waves whichFig21.1Spectrum

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haveverylongorshortwavelengtharenotvisibletooureyes.MutuallyperpendicularelectricandmagneticfieldswhicharealsoperpendiculartothelineofpropagationareknownasElectromagneticwaves.Theyhelpintransportingenergy.Theytravelwithavelocityof3x108ms-1 invacuumthatis3lakhkilometrepersecond.

Fig21.2Electromagneticwave

Fig21.3Usesofelectromagneticwaves

Soundwaves,wavesonwater,springwavesarealldifferentkindsofwaves.Theyarecalledmechanicalwaves.Theyneedamediumtotravelandhavecomparativelyverylessvelocitythanlightorshallwesayelectromagneticwaves?

Allelectromagneticwaveshavethesamevelocityof3x108 ms-1invacuumbut theydiffer fromoneanother regardingwavelengthandfrequency.Recallthetermsfrequency,wavelengthandamplitudethatyouhavestudiedunderthechapterSound.

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Numberofcyclespersecondiscalledfrequency.ItsunitisHertz.10kilohertziswrittenas10KHzor10000Hz.Distancebetweentwoconsecutivecrestsortroughsiscalledwavelength.Heightordepthofawaveiscalledamplitude,whenitisrepresentedbyagraph.

Electromagnetic waves are broadly arranged in the increasingorderof theirwavelength insevencategories.Thoughtheyhave thesamevelocity,theydifferfromoneanotherregardingwavelengthandfrequency.Someofthemareharmfultohumanhealth,yetusefulinindustrialandmedicalfield.

Whyshouldweknowaboutelectromagneticwaves?Itisbecausetheyactlikevehiclesinmostofthemoderncommunicationdevices.

JamesClerkMaxwell HeinrichRudolfHertz

Electromagneticwave theorywasfirstproposedbyJamesClerkMaxwell,intheyear1864.TheywerefirstexperimentallyproducedanddemonstratedbyHertzintheyear1887.ElectromagneticwaveswerecalledHertzianwavesinthebeginning.

Theuseofelectromagneticwavesinsendingwirelessmessagesorradiocommunicationwasfirstdemonstratedby the IndianscientistAcharya Sir Jagadish Chandra Bose two years beforeMarconi’sdemonstration. J.C.Bose’s demonstration of radio communicationwasconductedin1895atTownhallofKolkatta.LieutenantGovernorSirWilliamMackenziewitnessedBose’sdemonstration.BosewenttoLondononalecturetourin1896andmetMarconi.Marconiwaswellawareof thedemonstrationofJ.C.Bose.Butheclaimed thepatent.

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J.C.Bosewasnotinterestedinpatents.Hemadehisinventionspublicsothatitmaybeusefulforfurtherresearchbyotherscientists.Bose’sidealisalsofollowedbyscientistslikeRoentgen,PierreCurriewhowerenotinterestedinpatentingonmoralgrounds.

J.C.BoseSir.J.C.Bosewasaphysicist,biologist,

J.C.Bose

botanist,archeologistandwriterofsciencefiction.Hewas a very popular PhysicsProfessor at the Presidency College,Kolkata.Hissemiconductordeviceswhichdetectedradiowavesarestillbeingusedin many forms o f modern radiocommunication.

Heisthefirsttoproduceelectromagneticwaves of 1 metre wavelength. Thesimilarities of plant and animal tissueswere shown by him.He used his owninvention the Crescograph tomeasureplantresponsetovariousstimuli.

RevaluationofscientifichistoryputsSir.J.C.Boseaheadofallinradiocommunication.

Guglielmo Marconi

GuglielmoMarconi

guglielmo marconi 1874-1937 HereceivedNobelPrizeinPhysicsin1909,forhisoutstandingworkinwirelesstransmission.Firstwireless stationswere started in 1926linkingEnglandandCanadaduetohisefforts.He hadmany patents to his credit. He isofficiallyrecognizedastheinventorofradio.

radio:Radioisstillthemostpopularelectronicdeviceusedtolistentomusic,speechesandweatherbulletins.Thelowcostdevicenamelyradioreceiverdoesnotrequiremuchtechnicalskillstooperate.

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Radiocommunicationinvolvestwothings

•Radiotransmitter

• Radioreceiver

radio transmitter Music,speechorweatherbulletinconsistofsoundwaveswhichare

producedbyvibrations.Thisinformationiscalled‘intelligence’.Thesesoundwavesareconvertedintoelectricalsignals,calledAudioFrequencywavesorAFinitsshortform.MicrophonesconvertthevibrationsintoAF. Inmicrophonesa thinfilmcalleddiaphragmvibratesby soundwaveswhicharetransferredtoacrystalwhichisgenerallymadefromquartz.Quartziscrystallineformofcommonlyoccurringsilicondioxide.

Crystals of such types produce electrical signalswhen they aresubjectedtostress.ThevariationsinAFareaccordingtothevariationsofthesoundwaves.

AFsignalsareweak.Theyarestrengthenedby electronic devices. The process ofstrengthening the AF signals is calledamplification.

TheamplifiedAFsignalseveniftheyarestrengthenedcannottravellongdistances.They need a transport vehicle to travellongerdistances.Thesevehiclesarenothingbutelectromagneticwavesofwavelength 1mto1km.

ElectromagneticwaveswhichcarrytheAFsignalsarecalledcarrierwavesorRadiofrequencywavesorRFinshort.

RFwavesareproducedseparately,usingoscillatorcoils,intheradiotransmitter.ThecontributionofH.RHertzregardingproductionofradiowavesofrequiredfrequencyshouldberememberedinthisregard.

EachtransmitterhasitsownvehiclethatmeansitsownRFwaves.InfactaradiostationisrecognizedbythefrequencyoftheRFwavesituses.

Bangalore radio station transmits radio waves of wave length 490.1m.Canyoucalculateitsfrequency?

Fig21.4Microphone

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Activity 21.1

With the help of a radio receiver set, tune the radio at different frequencies. You will listen to the programme of that radio station.

Try to find out frequency of some radio stations which are frequently used by you or by your parents.

Think: If two or more persons start talking to you simultaneously, how do you feel ?

If two radio stations have the same frequency, what will happen?

If you know the wavelength you can calculate the frequency.

Velocity = Wavelength × Frequency or Frequency = wavelengthvelocity

= 3 x 108 m s-1 =30,0000000 m per second

Wavelength of a station = 300 mTherefore frequency of the radio station 300

300000000=Hz106

-

10 K Hz3-

The process of superimposing or mixing AF signals on RF waves is called modulation. The modulated waves are further amplified and transmitted by transmitting towers or antenna. The RF wavelengths in the range of 10 m to 100 m, get reflected by the ionosphere of the earth. The transmitted modulated wave covers large distances. This is the major advantage of radio communication. FM stations or TV sta-tions use high frequency waves which pass through ionosphere and are not bounced. Relay stations or satellites are needed for long distance communication of such stations.

RF AF Modulated wave

Fig 21.5

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Block diagram of radio transmitter

Fig21.6Blockdiagramofradiotransmitter

radio receiver

Todaytherearevarietyofreceivingsets.Tolistentotheparticularstation the radio should be tuned to that station.Built in antennareceivesthemodulatedwaves.

DetectorseparatesRFfromAFsignals.The

Speaker

process of separatingRFwaves fromAFwaves is called demodulation. The AFsignalsareamplifiedandfedtothespeakerto reproduce theoriginalsound.Speakerworksinthereversemannerofmicrophone.In this the coil starts vibratingwhenAFsignalsarepassedthroughit.Thevibrationsaretransferredtoadiaphragmtoproducesoundwaves.

Fig21.7Blockdiagramofaradioreceiver

television

Whensoundwavescanbe transmitted to longerdistances,whynotthelightfromtheobjects?Inradiotransmissionsoundenergyisconverted intoAF signals. Is it possible to convert light energy intoelectricity?

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Youmighthaveheardaboutphotocellswhichconvertlightenergyinto electrical energy. The idea took a shape by the experimentsconductedbyJOHNLOGIEBAIRD.

JohnLogieBaird

John Logie Baird J.L.Bairdwas a Scottish engineer,who isbestknownastheinventoroftelevision.HisdegreecoursewasinterruptedbyWorldWarIandhenevergraduated.

Usingdiscardedpartsofabicyclelamp,atorch,oldmotor,partsofadiscardedradio,he tried to send the visual signals usingelectromagneticwaves.

In 1930 from his London studio hesucceeded inmaking the face of a popularsingerappearonascreenforashortwhile.His experiments were used later for warpurposes.Afterthewartherewastremendousdevelopment.

how does a t.V. work ?

TheimageofanobjectismadetofallonaplateusingT.V.camera.This plate is called signal plate. The plate consists ofmany photocells.ThelightfromtheobjectisconvertedintovideosignalsorvideofrequencywavesorVFinshort.Beforethisprocesstheimageisscannedasdotsandlinesbythescanner.Normallycathoderaytubeiscalledscanner.TheVFsignalsareamplifiedandmodulatedonRFwaves.Themodulatedwavesareamplifiedandtransmittedthroughantenna.Soundistransmittedasinaradio.

Fig21.8BlockdiagramofaT.V.Transmitter

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t.V. receiver Antennareceivesthemodulatedwaves.Channelselectionisnothing

but selection of frequency of a T.V. station.After demodulation,VFsignalsarefedtothepicturetubecalledcathoderaytube.Thecathoderaytubeproducesoriginalpicture.Thesoundisreproducedasinradioreceiver.TodaythereisrevolutioninthefieldofT.V.receiversets.HugepicturetubesarereplacedbydigitalpicturetubesorflatplasmaT.V.screens.

Fig21.9BlockDiagramofaT.V.Receiver

Know this : T.V. Transmission requires high frequency carrier waves.TheyarenotbouncedbyIonosphere.Theyneedrelaystationsfordistanttransmission.GeostationarysatelliteslikeINSATseriesaremostusefulindistantT.Vtransmission.OneGeostationarysatellitecanlink1/3oftheglobebyT.Vnetwork.

Know this : The remote control handset of T.V makesuse of infra red radiations of very low frequency of lowtemperature.Dependingupon the frequency of the infrared radiations emitted by remote control, a channel isselected,bytheinfraredsensor.

FaX how does it work ?Thelongformoffaxisfacsimiletransmission.Alltypesofdocuments,

eitherprintedorhandwritten,linediagramsandphotographscanbesentorreceivedusingthefaxmachine.Itisdifferentfromelectronicmail.Informationissentthroughtelephoneline.

Afaxmachinescansthedocumentbylightandtheimageischangedinto electrical signals by photo cells. Themessage travels throughthetelephonelinesandreceivedbythefaxmachineattheotherend. Afterde-coding,machineproducesthecopyoftheoriginaldocument.Everyfaxmachinehasanumberlikeatelephone.Thishastobedialedbeforesendingamessage.

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Fig 21.8 Fax Machine

Fig 21.10 Fax Machine

Alexander Bain invented fax. He was a Scottish instrument inventor, technician and clock maker. He invented electric clock. Bain also installed the railway telegraph line.

TelephoneThe trin-trin sound of a telephone is very familiar to you. You might

have also used the coin booth. The sound waves are converted into electric signals by the mouth piece. The signals reach the ear piece at the other end by cables.

There are many developments in the technology of telephone. Instead of using traditional copper cables, we are using optical fibres and light, preferably laser light. Recall ‘total internal reflection of light’ in the chapter light. In a small space thousands of lines can be put. Telephone is a two way cabled communication device.

Alexandar Graham Bell

Telephone was invented by Alexandar

Alexandar Graham Bell

Graham Bell. He was a British inventor, Scientist, Engineer and professor. Above all he was a teacher for the deaf.

The knowledge of the structure and functioning of Human ear inspired him to invent telephone.

Cellular telephone exchange system uses computerized techniques. This has solved many problems of mechanical exchange system. You are already familiar with terms like :

STD: Subscribers Trunk Dialing

ISD : International Subscriber Dialing

Each transmitting unit has its own code. For example Bangalore code is 080. This number has to be dialed first and then the telephone number for calling on the persons of different exchange areas.

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mobile

MartinCooper

martin Cooper

MartinCooperinventedthehandheld cellularmobile phone.Hewasan American Engineer. Hewas theDivisionalManagerandVicePresidentofMotorola.

Howdoesamobilework?Theworkingofmobileissimilartotheworkingofradio.Mobileisa

twowayradiosystem.Itconsistsofbothradiotransmitterandreceiver.Italsoconsistsofaportablemicrochipcalledasimcard(SubscriberIndexModule)anda lithium-ionre-chargeablebattery.Allof this isgenerallyencasedinahardplasticframe.Itcontainsdisplayscreenandminikeyboard.

Todayyoucomeacrossavarietyofmodelswhicharemultifunctional.Theyincludealarmclock,calculator,camera,musicplayer,games,ShortServiceMessage orSMS. Internet services andMultimediaMessageService(MMS)arealsoavailablewithsomemodels.

The soundwaves are converted into radio frequencywaves andtravelwithoutthehelpofcablesandreachareceiveratnearbybasestation.Thebasestationsendstheradiowaveswhicharedetectedbythereceiver. Messagesarealsotransmittedandreceivedthroughthebasestation. Mobileusersoftenusethewordroaming.Whatisit?

Roamingmeans transferring the service of a home network to another service provider. In simplewords itmeans interlinking twonetworks.advantages of mobile

• Communicationbetweentwopersonseveniftheyaremoving• Communicationtoandfromalandlinephone• Voicemessage,textmessagefacilities.

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• Itcanbeusedasaminicomputer.

• Linking of entire globe by telecommunication using geo stationarysatellites.

Find out : Microwavesareusedinmobilecommunication.Withtoomanyusers,themobiletowersarealsoincreasing.Theeffectofmicrowaveswhichhavehigherfrequencythanradiowaves,onhumanhealthandalsotheireffectonbirds,animals,plantshavetobestudiedindetailforinventingsafeguards.

Fig21.11MobileServicethoughsatellite

internet

Withacomputerandtelephoneconnectionlinkedtothenetworkofinternetservice,youcanhaveaccesstoanykindofinformationbeitmusic,film,encyclopaedia,newsupdate,profilesoffamouspersons.Youcandownloadanyinformationonanyofthesubjectandaprintoutcanalsobetaken.

Activity 21.2

Learn to access Internet services. Create your own E-mail address and try to send and receive information by E-mail in school computer laboratory if available. Visit a nearby cybercafe. Learn to access internet services. You can also learn it in your school if internet facilities are available.

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exercises :

i. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer.

1. Modulatedwavesofradiotransmittercontain, a. soundwaves b.carrierwaves c. AFwavesandcarrierwaves d.AFwaves.2. IncreasingthestrengthofAFwavesiscalled. a.modulationb.transducingc.demodulation d.amplification3. Telephonewithcableswasinventedby. a. AlexanderGrahamBell b.AlexanderBain c. MartinCooper d.JohnLogieBaird.4. A person is singing in a Radio station. It can be listened to in a

receiveralmostataspeedof. a.sound b.lightc.1/16thofasecond d.1/10thofasecond

ii. Fill in the blanks : 1. Thedevicethatcanbeusedtosendacopyofadocumenttoother

placesquicklyis___________________.2. Originalsoundisreproducedinaradioreceiverby_______________.3. Firstpersontodemonstratetransmissionofradiosignalsis______.4. Twowayradiocommunicationdeviceiscalled__________________.5. Radiocommunicationoflongdistanceispossiblewithoutsatellites

duetothepresenceofatmosphericlayer___________________.6. Microwavesareusedin___________________phones

iii. answer the following :1. Whatareelectromagneticwaves?2. Whatismodulation?3. Whichpartoftheradiotransmitterconvertssoundwavesintoaudio

frequencywaves?4. Which part of the T.V. transmitter converts light into electrical

signals?5. Drawaneatblockdiagramofradiotransmitter.6. Theprincipleofradioandmobilephoneisthesame.Howarethe

twodifferentfromoneanother?

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Chapter 22

Food produCtion–soiL and water management

after studying this chapter students :• describetheimportanceofmanagementofsoil

• listthevariouspracticesinvogueforrationalmanagementofsoil

• describebrieflyeachofthevariouspracticesfollowedforenrichmentandmaintenanceofthesoil

• listtheadvantagesanddisadvantagesofgreenrevolution

• describetheadvantagesanddisadvantagesoforganicmanuresandchemicalfertilizers

• list the various types of chemical fertilizers commonly used by farmers

• statethetypesofnutrientsaddedtothesoilbytheuseofvarioustypesofchemicalfertilizers.

• describesomeofenvironmentalfriendlyfarmingpractices

• appreciatethecontributionsofIndianstothefieldofagriculture

Wehavestudiedmanythingsaboutfoodandnutrients.Shouldwenotknowfromwherewegetourfood?Asyouknow,mostofusprocurefoodfromanoutsidesource.Onemayobtainfoodinthreeprincipalways:

• Somepersonsobtainfoodbyhunting,fishing,gatheringwildfruits,edibleleavesandrootsofplantsinthewild.

• Somepersonsproducefoodbycultivatingcertainplantsanddomesticatinganimals.

• Manypersonsbuyfoodfromthemoneyearned.

Youareinthesecondgroup,ifyouareborninafarmingfamily.Restofusallfall intogroupthree.Whatevermaybethecase,someonemustgrowfood.Thelawofnatureisthatmostorganismsthrivebyeatingotherorganisms.Plantsusesoilminerals,water,airandenergyfromthesuntomanufacturetheirownfood.Animalseatcertainplantsorplantproducts.Humanseatbothselectedplantsandsomeoftheanimalsortheirproducts.Theprimarysourceoffoodforhumansisthe

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plant.Thesecondarysourcesareanimalssuchasgoats,poultrybirdsandanimalproductssuchasmilkandeggs.Thus,allorganismsgettheirfooddirectlyorindirectlyfromplants.Naturallyavailablefoodareinsufficienttofeedthemouthsofever-increasingpopulation.Hence,wehavetakentoagriculturewhereinwecultivatecertaintypesofplantsinagivenlandarea.Withoutagriculture,whichinvolvesthetoilandsweatofthefarmingcommunity,theworldcannotsurvive.Whetheroneisrichorpoor,engineerorlabourer,everyonedependsonthefarmersfortheirfood.Thatiswhywecallthem ‘annadathas’.

‘agriculture’ isthescienceandartofcultivatingcrops,andraisinglivestock.Itwasoncethechiefwayoflifeinnearlyeverycountry.Peoplecannotlivewithoutfood,andnearlyallourfoodcomesfromcropsandanimalsraisedonfarms.Manyothermaterialssuchascottonandwoolalsocomefromplantsandanimalsraisedonfarms.Agricultureremainsthemost importantoccupation intheworld.Scientificmethodsandmachineryhavemadefarmingincreasinglyproductive.Thedevelopmentof improvedplantvarietiesand fertilizershashelpedto improve theyieldsofsomemajorcrops.Scientificlivestockcareandbreedinghavehelpedincreasetheamountofmeatandproductsthatanimalsproduce.Atthesametime,theuseoftractorsandothermodernfarmequipmenthassharplyreducedtheneedforfarmlabour.

For getting best out of agriculture, the farming community needs

• Goodseeds

• Availabilityoffertileland

• Waterandirrigationfacilities

• Manuresandfertilizers

• Supportivesocialandeconomicenvironment

• Croppricingpolicy

• Goodpricesfortheirproduce.

• Scienceandtechnology

Canyouthinkofanyotherfactors,discusswithyourfriendsandteachers.

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InIndia,agricultureisstillthelargestoccupation,engagingalargesection of our population. The success of our nation, our economydependscritically on thequalityandeffectiveoutputof agriculture.Severalfactorsinfluenceagriculture.Agricultureisahighlycomplexbutaveryimportantenterprise.Hence,itisimportantforustorealizethevastdimensions,problemsandachievementsinthefieldofagriculture.

By now, you should have an idea regarding the complexities,problemsandchallengesincropproduction.Letusnowconsidertheissuesrelatedtosoilandwater.

importance of soil in agricultureWhatissoil?Itwouldbewrongtothinkofsoilsasjustacollectionof

finemineralparticles.Soilalsocontainsair,water,deadorganicmatter,andvarioustypesoflivingorganisms,althoughwemustrecognizethatthecompositionofthesewillvaryfromplacetoplace.

Differentpeopleviewlandandsoildifferently.Landanditssoilisameansoflivelihoodforthefarmingcommunity.Fortheurbanitesitis,aplacetoconstructbuildings.Toachild,itisaplaceandathingtoplay.Itisastorehouseofmineralsforaminer.Humanistsseelandandsoilasmaterials,whichdeterminetheexistenceofallformsoflifeonearth.Whatisyourview?Whatdoessoilmeantoyou?Soilplaysamajorroleinallhumanactivities.Infact,allofusgetourlivingdirectlyorindirectlyfromthesoil.Sodoeseveryotherlivingorganism.

Soil isanasset thatwecanhandover to countlessgenerationsalmost intact.Crops takeup their requirements suchaswater andmineralsthroughthemediumofsoil.Soilalsoprovidesanchorageforcrops.Itistheprimarynutrientreservoirforplants.Thus,agriculturehighlightstheroleofsoilintheproductionoffood.

need for soil managementSoil isoneofthemajorfactorsthataffectfoodproduction.Crop

plantsneednutrientsfortheirliving,healthygrowthandhigheryields.Cropswellfedwithnutrientsarelikelytogrowfast,remainstrongandthereforeshowresistancetodiseases.Cropsthatgrowinsoildepletedwith nutrientswill show slow growth andmay even die.Hence, itis importanttomaintainthequalityofthesoil.Soil thathashighercapacity tosupply therequirednutrients is fertile soil.Conversely,depletedsoilisunabletoprovidenutrientsandsupport.Naturalandhumanfactorscontributetothedepletionofsoil.Thismakesthesoil

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increasingly less productive and renders agricultureunsustainable.Hence,weneedtomanagethesoiltomaintainitsqualityandfertilitytoenhanceitsperformance.Theproductivityandperformanceofsoildependsonseveral factors.They includesoil fertility,water supply,land-slope,depthtothewatertable,climateandcultivation

Soilless cultivation

Canwegrowcropswithoutusing soil?Human ingenuityhasmadeitpossible.Atechnologythatenablesgrowthofcertaincropswithoutsoilisavailable.Itinvolvesgrowingplantswiththeirrootsinnutrientsolutionsandwithoutsoil.Thisisknownashydroponics. Wealsocallit‘soillesscultivation’.

Aplantisakindofbiologicalfactory.Itrequiresalargenumberof rawmaterials.These includecarbon,hydrogen,oxygen,nitrogen,phosphorus,potassium,sulphur,magnesium,calcium,iron,manganese,zinc,copper,boronandmanyothers.Plantsgetcarbon,hydrogenandoxygen fromairandwater.Mostof theothernutrientsarerequiredonly in smaller quantities. Theyarepresent in the soil in sufficientamount.Theproblemiswiththeavailabilityofnitrogen,phosphorusandpotassium.Lackof oneormoreof these in thesoil limits cropproduction.Hence,itisamajorconcernforthefarmingcommunity.Itistheamountofthesethreenutrientsalongwithhumus,whichusuallydeterminesoilproductivity.Weshalllearnaboutthewaysofmaintainingthesethreenutrientslaterinthechapter.

techniques of soil managementSoilmanagementconcernsalloperations,practicesandtreatments

usedtoprotectsoilanditsfertilitysothatcropscangrowandyieldwell.Undernaturalconditions,allplantmaterialsreturntothesoil.Therefore,thefertilityofthesoilwillneverdecline.Thisisthecasewithforestsorgrasslandsuntouchedbyhumanactivity.Whenwegrowacrop,wetakeoutallorapartoftheplantproduce.Thisisnecessarytofeedpeopleanddomesticanimals.Thisresultsindepletionofthesoilproductivity.Intenseandprolongedagricultureinagivenlandcausesafallinlandproductivity.Luckily,sciencehashelpedustounderstandthefactorsthataffectsoilproductivity.

Science has also given usways ofmanaging andmaintainingthe quality of the soil. Figure 22.3 summarizes these techniques.Maintenanceofsoilproductivityinvolvestwomajorissuesnamely;

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• identificationofthewaysandpreventionoflossofnutrientsinthesoil

• takingstepstomaintainandrestoresoil fertility.Hereareafewtipstomaintainsoilfertility.wemayalsocallittechniquesofsoilmanagement.

techniques in soil management

• Controlerosionoftopsoil.

• Maintainthewaterbalanceandregulatesoiltemperature.

• Improvethesoilstructureandmaintainastockoforganicmatter.

Activity 22.1

Can you think of any other points. Speak to a farmer and gather information.

Thevaluablenutrients inthesoilareeither lostor takenout inmanyways.Whenweharvestcrops,weremovelargestamountofsoilnutrients.Canweavoidthisloss?Erosionofthetopsoilalsodepletesnutrients insoil.Nutrientsarealso lostwhenrainwateror irrigatedwatertakesawaysolublenutrients.Howcanwepreventthisloss?

activity 22.2

Collect information about soil erosion and make notes on the causes of soil erosion and ways of preventing it. Exchange the information with your friends. Do you think that soil erosion is a serious problem? What types of agricultural practices will reduce soil erosion? What are the other problems that arise by soil erosion? Also, find out the meaning of the word ‘leaching’. How can you prevent the loss of nutrients caused by leaching? Is there a loss of nutrients in your home garden or school garden? What measures do you suggest to prevent this?

Wecantakemeasurestomaintainorrestorethesoilnutrients.Doyouknowanyofthese?Suchmeasuresincludethefollowing:

proper use of land

Wecanreducenutrientlossfromthesoilbyusingthelandonlyforthosecropsforwhichitisbestsuited.Itisbettertomaintainapermanentgreencoveronlandssuchassteepslopesthatareparticularlyvulnerabletoerosion.Failuretodothismeansmoreerosion,whichrendersthelandunusableforagriculture.For instance,wefindlargechunksofsuchunusablelandintheChambalregionsofMadhyaPradesh.

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Crop rotation

Crop rotation is one of the oldest and effective strategies formaintainingsoilproductivity.Manyfarmersgrowseveraldifferentcrops,oneafteranother,inaregularsequence.Thisisbetterforthesoilthangrowingthesamecrop,seasonafterseason.Incroprotation,thecropforanewseasonisfromadifferent‘family’thanthepreviousone.Theplannedrotationmayvaryfrom2to3yearsorlonger.Wemaygrowpaddyorragiinoneseasonfollowedbyalegumecroplikegroundnut.Thisisalessintensivetypeofagriculturethansinglecropping.IsthispracticesuitableforacountrylikeIndiawheregrainneedsarehigh?Think.Whatisyourviewonthis?

Croprotationalsohelpstokeeptheinsect-pestpopulationundercheck.Generally,insectpestsanddisease-causingorganismsarehost-specific.Forexample,ricestemborerfeedsmostlyonrice.IfyoudonotrotatePaddywithothercropsbelongingtoadifferentfamily,thepestpopulationincreasesbecausefoodisalwaysavailable.However,ifyouplantlegumeasthenextcrop,theinsectpestislikelytodieduetonon-availabilityoffood.

Howdoescroprotationhelptopreventthelossofnutrients?Croprotationgiveshigherprotectionagainstsoilerosion.Cropsthatgrowcloselytogethergreatlyhelpinpreventingsoilerosion.Croprotationalsoprovidesdifferenttypesofrootsystems.Someplantshavedeeperroots.Somespreadhorizontallywhileothersgodeep.Rotatingsuchcropsenhancessoil fertility.HaveyouheardofbacteriacalledRhizobium? Wheredothey live?Howdoes ithelptomaintainthe fertilityof thesoil?Findout.

mixed cropping and multiple cropping

Inmixed cropping, farmers sow onemain crop and one or twosubsidiarycropstogetheronthesameland.Mixedcroppingtechniquecanbe followedboth indryandwet lands. In this technique,cropsutilize soil nutrientsmore evenly. There is no extensiveuse of anysingle nutrient. This also provides some kind of security for thefarmingcommunityagainstcropfailure.Anotheradvantageisthatitsecuresthefamilyrequirementsofcereals,pulses,oilseedsandfoddersimultaneously.

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Thereislimitedlandavailableforagriculture.Hence,wemustfindwaysofincreasingtheyieldperhectare.Onewayistogoformultiplecropping.Wemustgrowmorethanonecropinayearorseason.Thisrequires good irrigation facilities and short duration breeds.We, inIndia,haveattemptedmultiplecroppingbyintroducingsuchcropsasbarley,potatoesandvegetablesinadditiontocropslikepaddy,maize,jowarandbajra.Whatdofarmersdoinyourregion?

Keeping the land unused

Somefarmersreplenishsoilfertilitybykeepingthelandunusedforaseasonortwo.Theyallowsheepandgoatstograzeandsitovertheland.Theirdroppingswillenrichthesoil.Thisensuresincreasedfoodproductioninthenextcroppingseason.

role of organic manures in soil management

Organicmatter in the soil consists of fresh organicmatter andhumus.Freshorganicmatterincludesdeadplantandanimalmaterial,andanimaldroppings.Soilorganismstransformsuchorganicmatterintofineorganicmatterandhumus.Humusinsoilimprovesthesoilstructure,resistssoilerosion,retainswater,andenrichesthenutrients.

Thepresenceoforganicmatterinthesoil isfundamentaltosoilproductivity.Widespreaduseofdecomposedorganicmattermaintainsandimprovessoilfertility.Organicmanureischeaper.Onlycostinvolved,isprobablythelabour.Organicmanuresbindloosesoil,increasetheirwaterholdingpower,helpinaeration,assistinpenetrationofroots,addplantnutrientsandincreasemicrobialactivitythatarehelpfulforcrops.

Wecanmakeorganicmanuresfromanyorganicmatter.Compostmadefromanyorganicwastessuchasanimaldung,nightsoil,sludge,sewage, sheep folding, and greenmanures. Edible and non-edibleoilcakes,bloodmeal,fishmeal,bonemealalsoprovideessentialnutrientstothesoilinrelativelyconcentratedform.Cattledungisprobablythelargestsourceoforganicmanuresforthefarmingcommunity.

Think : Manyfarmingfamiliesusecattledungtomakecakes.Theyusethesecakesasfuelforcookingandheatingwater.Whatarethedisadvantagesofthispractice?Howcantheygetbothmanureandfuelfromcattledung?

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Wemustaddorganicmanures in relatively largequantities.Wemustaddthembeforethesowingorplantingofsaplings.Whyisitnotsousefultoaddorganicmanuresinthemiddleofthecroppingseason?Whatoptionsdothefarmershave?

preparation of compost

How canwemakemanure from organicmatter? The naturaldecompositionprocessconvertscomplexorganicmatterintomanure.Wecanhoweverregulateandspeedupthisprocess.First,wemustcollectandstackuptheorganicmaterialinaheapinsideapitorvessel.Thedecompositionismoreintenseinaheap.Thisisbecausetheconditionsfordecompositionaremorefavourable.Theproductiscompost,whichisnothingbutwell-decayedorganicmatterwithhumusandnutrients.

Activity 22.3

You may want to prepare compost for your kitchen garden. You can do that without much cost. Knowledge you gain from this experience may help you understand some of the practices followed by farmers. The concept of ‘Thippe’ is an example of such practice. Do you have a small place around your house or school? You can make compost even in a bucket or a plastic bag. Dig a pit. Put any organic waste such as vegetable peels, Cowdung, fallen leaves from trees, crop residues or even weeds into the pit. Make them into small pieces if they are too large. Pour a layer of soil over them. Sprinkle water over the soil to keep the matter moist. Go on heaping layer after layer until the pit or the bag is full. Keep adding water after each heap. Microbes break up the organic matter into simpler forms. Adding a few earthworms will also help. Leave it for 8-10 weeks. Compost is now ready for use.

Bio-fertilizers

Sometimes farmers add livingmicroorganisms likeRhizobium, Azotobacter, Azolla, Nitrobacter andPhosphotika to the soil. Addingsuch organisms increases soil fertility and promotes plant growth.Theseorganismsaddupnutrientsbytheiractivityandhelptobuildupthefertilityofsoilandsafeguardthequalityofcropproducts.Forinstance, organisms likeRhizobium, Azotobacter, Acetobacter, andblue-greenalgaehelptomobilizenitrogen.AbiofertilizerlikePhosphotika mobilisesphosphorus.

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role of chemical fertilizers in soil management Chemicalfertilisersplayanimportantroleincropproduction.They

aresyntheticallypreparedtoincludethevitalnutrientsessentialfortheplantgrowth.Theycontainthenutrientsinspecificratiosinareadilyusableform.Wemayadjusttheirdosagetosuittherequirement.Wecaneasilyassesstherequirementbysoiltesting.Farmersmaychoose,dependingontheneed,tousefertilizersthatprovideasinglenutrientormixedfertilizers.Mixedfertilizerssupplytwoormorenutrients.Forexample,NPKhasnitrogen,phosphorusandpotassium.Monopotassiumphosphatehashighcontentofbothphosphorusandpotassium.Ureaisafertilizerwhichprovidesonlyonenutrientnamelynitrogen.

Oneofthebenefitsofchemicalfertilizersisthatitiscustom-madeforyour requirement.Ifsoilinyourfarmlandisrichinnitrogenandpotassium,what youneed is a fertilizer thatwill take care of the phosphorusdeficiency.Chemicalfertilizerswillgiveyoutheoptiontouseonlythatnutrientwhichisindeficiency.Further,chemicalfertilizershavehighNPK(Nitrogen,Phosphorus,Potassium)ratioofnearly60%.Mostfertileoforganicfertilizerscangiveonlyabout14%.Chemicalbasedfertilizersare cost-effective and can supply plantswith the proper balance ofNitrogen,PhosphorusandPotash.

problems of chemical fertilizersChemicalfertilizersaddseveralsaltstothesoil.Someofthesehave

atendencytoaccumulateandalterthesoilcharacteristics.Thismayharmanddestroythesoilfauna.Increaseduseofchemicalfertilizersalsocausespollutionoflandandwater.Thisaffectstheaquaticorganismsandtheirhabitats.Thus,achainofundesirablechangestriggerintheenvironment.

alternate agricultural practices for soil conservation organic farming

Modern technologieshad theirproblems.This gavemomentumtomore eco-friendly agricultural practices.organic farming isthe form of agriculture that relies on techniques such as croprotation, green manure, compost, and biological pest control,to maintain soil productivity and control pests on a farm. Organic farming strictly limits the use of chemical fertilizers andsyntheticpesticidesandmedicines.

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Theorganicfarmingmovementbeganinthe1930sand1940sasareactiontoagriculture’sgrowingrelianceonsyntheticfertilizersandpesticides.Today,variousgovernmentsaremakingeffortstopopularizeand promote organic farming. States likeKarnataka,Maharashtra,MadhyaPradesh,Gujarat,TamilNaduandKeralaareshowinggreaterkeennessinorganicfarming.

water managementWeallknowthatwaterisacriticalinputforagriculture.Willtherebe

enoughwatertogrowenoughfoodforallourpopulation?Itisprobablethatourpresentpracticesofwaterusewillleadtoseverewaterandenvironmentalcrisesinmanypartsoftheworldinthecomingdecades.Agriculturalwatermanagementis increasinglyimportantbecauseoflowwater supplies. Better agriculturalwatermanagement ensuresavailabilityofadequatewaterfordrinking.Lackofwaterisaconstrainttoproductionoffoodgrains.Thinkingdifferentlyaboutusingwaterisessentialforachievingourtriplegoalofensuringfoodsecurity,reducingpoverty,andconservingecosystems.

Productionoffoodandother

Fig22.1Usageofwater

agriculturalproductstake70%ofthe freshwater from rivers andgroundwater. There is a seriouscompetitionforwaterforvarioushumanactivitiesfig.22.1showsrelative requirementofwater forag r i cu l tu re and domes t i cconsumption.Water disputes invillagesarecommon.Wearealsoawareofinterstateandinternationaldisputes overwater. Can you think of some of them? This raisesimportantquestions.Whowillgetthewater?whodecidesallocations?Shouldwesupplywaterforfaroffcitiesortothenearbyfarmlands?Shouldpeopleinupstreamgetmorewaterthanthoseindownstream?

The competition forwater is not just betweenhumanbeings ofvariousshades.Waterusedforagricultureisatthecostofwatersupplytoothersareas,plantsandanimals.Thismayevencausechangesinecosystemtoo.

Ourenvironmentisunderthreatfromouragriculturalpractices.What practices are harming the environment and the ecosystem? Theproblemwillgetaggravatedandbecomesunmanageableifwedo

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notaddresstheissuenow.Howcanwemanageourwaterresources?Howcanwegetbetteryieldsbyusing lesswater?Doyouhaveanysuggestions?Know this : Waterisapreciouscommodityforallformsoflife.Tofocusattention on the importance of freshwater and to promote sustainablemanagement of freshwater resources, the world observes InternationalWorldWaterDayeachyear.

United Nations Conference on Environment and Development (UNCED)in 1992 recommended the observance of WorldWater Day. The UnitedNationsGeneralAssemblydesignated22ndMarch1993asthefirstWorldWater Day. Each year, World Water Day highlights a specific aspectof freshwater. Do you observe such important days in your School?

Efficient management of water in agricultureEfficientirrigationcombinestwofactors:managingyourwaterto

applytherightamountattherighttime,andinstallingandmaintaininganenergy-efficientirrigationsystem.Goodwatermanagementmeansmatching the supply of irrigationwaterwith crop’s demand. Lesserthewateryouwaste,thelesserwouldbetheuseofelectricity.Goodequipmentdesignandmaintenancemeansthatyoursystemshouldsupplymostwater possible for eachkilowatt-hour of electricity youuse.Theseprinciplesarethesameformanagingasmalllawnoralargecommercialcrop.

Fig22.2Plantswithdifferentrootzones.

Toimprovewatermanagement,oneshouldfirstlearnaboutcropanditsrootsystem.Efficientirrigationwilljustsaturatetherootzone.Itdoesnotcausesurfacerunofforallowwater to percolate below the rootzone.Timingisalsovitaltoefficientirrigation.Whenyoulearntojudgetheamountofwaterinthesoil,andyouunderstandyourcrop’stoleranceto soil-water depletion, you willknowhowmuchwatertoapplyandwhen. These factorswill togetherdetermine the percent of applied

waterthatendsupintherootzone.

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Think : Observetheplantsshowninfigure22.2.Whichoftheplantsneedmorewater?Whydoyouthinkso?

Fig22.3Factorsinfluencingagriculturalwatermanagement

Efficientirrigationsystemsmustmaximizeefficiencyandminimizelabourandcapitalrequirements.Whenitcomestoefficiency,questionssuchaswhentoirrigate,howmuchtoapply,andcantheefficiencybeimprovedbecomeimportant.Thetypeofirrigationsystemfarmersfollowwillvaryfromlocationtolocation,croptocrop,yeartoyear,andfarmertofarmer.Figure22.3givessomeoftheimportantconsiderationsinirrigationpractices.

Some factors influencing the irrigational practices

Activity 22.4

Observe figure 22.3 carefully. It lists some important factors that influence the irrigational practices. Study them carefully. Give one example to show how each factor influences agricultural water management. Exchange ideas with your friends.

Therearetwobroadclassesofirrigationsystems:1.gravityflowdistribution,and2.pressurizeddistribution

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Gravity-flowsystemisthetraditionalpracticeofsurfaceirrigation.Furrowirrigationisanothernameforgravity-flowsystems.Water,inthesemethods,flowsfromthesourceanddistributedtothefieldthroughopencanalsandditchesbygravity.Farmerscontrolwatermovementanddirectittothefield.Theyreleasewateralongtheupperendofthefield.Waterflowstothefieldbymeansofopenditches,abovegroundpipeorundergroundpipe.

Pressurizedirrigationsystemconsistsofanetworkofpipes,fittingsandotherdevicesdesignedandinstalledtosupplywaterunderpressuretothefarmland.Thepressurizedsystemsincludesprinklerandtricklemethods.Thesesystemsarehighlyefficientirrigationpractices.Waterdistribution in thesemethods happens through pressurized pipenetworks. A suitable pumpusually provides the required pressure.Figure22.4givesacomparisonbetweenthevariousirrigationpractices.

DripirrigationSprinklerirrigationFurrowirrgiation

Fig22.4Comparisonofthethreeirrigationsystems.

Activity 22.5

Study the two types of irrigation systems listed above carefully. List the advantages and disadvantages of each of these systems. Tabulate your findings.

green revolution in india

green revolution refers to theboominagriculturalproductionthatresultedfromtheintroductionofhigh-yieldingvarietiesofseeds,increaseduseof fertilizersand introductionof improved irrigationalpractices.WilliamGaud coined thisword in 1968. The revolutioninvolved a series of research, development and technology transferinitiatives. The initiatives involved the development of high-yieldingvarieties of cereal grains, expansion of irrigation infrastructure,

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anddistributionofhybridizedseeds,syntheticfertilizers,andpesticidesto farmers.All IndiaRadioplayedacrucial role in theeducationoffarmersonvariousaspectsofgreenrevolution.ThesestepssignificantlyincreasedthefoodyieldperunitoflandbothinIndiaandworldwide.The impactofgreenrevolution in Indiawasmore impressiveontheproductionofwheatandrice.

SomepeoplenowblamethismovementforcausingLanddegradation,pollutionofwater,environmentalharmandfarmers’suicides.Thegreenrevolution,despiteitssuccess,hasnotreallyhelpedtoremovehungerfromtheworld.Therearemorethan800millionpeoplesufferingfromhunger.Abouttwo-thirdsoftheundernourishedintheworldliveinAsiawheregreenrevolutionwasagreatsuccess!GreenRevolutioncertainlyreduced India’s grain imports substantially, but did not eradicatehunger! Nearly one-third of our population is poverty-stricken andundernourished.About5000childrendieeachdayfrommalnutrition.

Think : Mere increase in food production and the availability of foodmaterials will not ensure freedom from hunger. What other factorscontributetothehungerandsufferingofthepeople?

architect of green revolution in india:

dr. m.s.swamynathan

Dr. M.S.Swamynathan, Indian

Dr.Swaminathan

agriculturalscientist,iscalledthefatherofgreenrevolutioninIndia.Swaminathanset inmotion fundamental changes inagriculturalproductioninIndiathathaveputanendtoIndia’sage-oldstatusasanationonthebrinkofstarvation.Heisanoutstandingscientistandresearcher.Hehasservedmanyagenciesandorganizationsasanadvisor,policymaker,andaboveallas a great leader. Hemade relentlesseffortstofindsustainablewaystoachievepeoples’basicrighttofood.Thegratefulnations have honoured himwithmanynationalandinternationalawardsandseveralhonorarydoctorates.HeisaFellowoftheRoyalSocietyofUKandoftheNationalAcademyofSciencesofUS

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agriculture in ancient indiaAgricultureisnonewvocationforIndians.Accordingtoarchaeological

findings,Paddywasacropgrownalong thebanksof theGanges in thesixthmillenniumBC.Later,itextendedtootherareas.Severalspeciesofwintercerealsnotablybarley,oats,andwheatandlegumessuchaslentilandchickpeaweregrowninNorthwestIndiabeforethesixthmillenniumBC. Archaeological research has also revealed the cultivation of severalothercrops3000to6000yearsago.

Rigveda mentions about productive and non-productive soils. TheAmarkoshadescribes12typesoflandsinitschapteronBhumivargaha. Fertilityandphysicalcharacteristicswerethebasisforthisclassification.ThechapteronVaisyavargahamentionssoils suitable for specificcropssuchaspaddy,barley,sesame,blackgramandsoon.Sangamliterature(200BCto100AD)ofTamilsinsouthernIndiaprovidesinformationonsoiltypes.

Ancient Indiansappreciatedthe importanceofmanures inobtaininghigh crop yields. Krishi-parashara states that crops grown withoutmanure will not give yield. It also describes a method of preparingmanure from cowdung. Kautilya mentions the use of cowdung, animalbones, fish, and milk as manure. Agnipurana recommends applicationof“excretaofsheepandgoat” to increasefloweringandfruitingof trees. InBruhat samhita,Varahamihirarecommendstheuseofsesameplantsas greenmanure. Surapala (1000 AD) describes the ancient practice ofpreparingliquidmanurecalledkunapa.

Indianknowledgebaseinmathematics,astronomy,andastrologywasstrong. Krishi-parashara and Bruhat samhita give simple models forpredictingrainsinaparticularseason.

Rigvedamentionsirrigationofcropsbyriverwaterthroughchannelsas well as irrigation from wells. Buddhist literature provides evidenceof building small tanks for irrigation. artha-sastra of Kautilya refersto sluice gates of tanks and mentions, “persons letting out the waterof tanks at any other place other than their sluice-gate shall pay afine of six panas; and personswho obstruct the flow of water from the sluice-gateoftanksshallalsopaythesamefine”.

People in southern India had developed extensive tank irrigationsystems during the first two centuries of the Common Era. Availabilityof irrigationmade itpossible to extendcultivationof rice to largeareas,andthusimprovefoodsecurity.AncientIndiansirrigatedtheirlandsfromwells.Bullockspulledaleatherbagwithropestodrawwaterfromwellsforirrigation.Theso-called“Persianwheel”usedfordrawingwaterfromwellswasfirstdevelopedinnorthernIndia,priortoinvasionsbyTurks.

surapala’s Vrikshayurvedamentionsmethodsofirrigationandwaystolocategroundwater,nourishmentofsoilandfertilizers.

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Know this : Several rulers in India gave priority for Agriculture. Thesagesprobablyhadconvincedtherulersthatprosperousagricultureisthefoundationforstrongempires.Thetraditionhadbeentoimposeminimaltaxonfarmers.WefindexamplesofthisinRamayanaandMahabharata.RamaaskshisbrotherBharata inChitrakoot,“DearBharata,haveyouensuredthatallthoseengagedinagricultureandanimalhusbandryreceiveyour special care and attention?” In Mahabharata, Bhishma, advisesKingYudhishthirain“Shantiparva”:“Agriculture,animalhusbandryandtrade are the very life of people.Have you ensured that the cultivatorsdonotdesertthecountrybecauseoftheexactionimposedbyyou?Itisindeedthecultivatorswhocarrytheburdenofthekingontheirshouldersandalsoprovidesustenancetoallothers.”Dowerecognize this today?

exercises

i. Four alternatives are given to each of the following incomplete statement /question. Choose the right answer:

1. rhizobium baceriaisassociatedwiththefixationof

a.oxygen b.carbondioxide

c.nitrogen d.watervapour.

2. Greenplants,normallydonotsufferfromthedeficiencyof

a.phosphorus b.sulphur

c.iron d.carbon

3. Oneoftheargumentagainsttoomuchuseofchemicalfertilisersisthatthey

a.decreasethetasteofthefoodb.reducethenutrientsinfood

c.affectsoilbacteria d.consumetoomuchinwater

4. Oneoftheadvantagesofgrowingchilliplantsbetweentworowsofgreengramplants,isthat

a.chilliplantsareprotectedbytheshadeofdhalplants

b.nitrogenousfertiliserpreparedbygreengramplantscanbeutilised bychilliplants

c.chilliplantsgetwaterfromgreengramplants

d.dhalplantsareprotectedfrompestsinthepresenceofchilliplants

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5. Pressurisedirrigationsystemhastheadvantageof.

a.washingawaypestsfromtheplants

b.conservationofwatertomaximumextent.

c.conservationoffertilizerinthesoil

d.productionofhydroelectricity.

ii. Fill in the blanks with suitable words:

1. FatherofgreenrevolutioninIndiais_____________________.

2. NPKfertiliserhastheelementsnitrogen,phosphorusand_________.

3. Ureawhichisachemicalfertiliserisarichsourceof_____________.

4. Byusinganimaldungandorganicwastewecanmakeanorganicmanurecalled_____________________.

iii. match the following :

A B

1. deeprootedplants a.donotneednitrogenousfertiliser

2. plantsthatarenotdeeprootedb.needalwaysrainwater

3. plantrootscontaining c.needchemicalfertilisers rhizobium

4. lossofwater d.occasionalwatering

e.frequentwatering

f.furrowirrigation

g.neednitrogenousfertiliser

iV. answer the following :

1. Listanytwoadvantagesandtwodisadvantagesofusingchemicalfertilizers.

2. Why should farmers enhance the amount of humus in their farmland?Howdotheydothat?

3. Distinguishbetweenorganicmanuresandchemicalfertilizers.

4. Listsomeagriculturalpracticesthathelptomaintainthefertilityofsoil.

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5. Howdoyoupreparecompostmanure?

6. List any three ways by which soil erosion occurs. State any two measurestoreducethelossoftopsoil.

7. Whataretheadvantagesoforganicfarming?

8. What are the advantages of pressurized irrigation systems over gravitydrivensurfaceirrigationsystems?

9. Suggestmeasurestoconservewaterinagriculture.

think

1. Whatisyourviewonorganicfarming?Ifyouweretohaveapieceof agricultural land, do you opt for chemical farming or organic farming?Givereasonsforyourchoice.

2. Howcanweensurefoodsecurityforallpeopleofourcountry?

3. Whyshouldwefindwaysforconservingwaterusedforagriculture?Whatareyoursuggestionsfortheconservationofwater?

4. Howcanwemakeagriculturemoreeco-friendly?

What we want are Western science coupled with Vedanta, Brahmacharya as the guiding motto. and also Shradha and faith in one’s own self.

-Swami Vivekananda

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Chapter 23eVoLution oF LiFe

after studying this chapter students :• understand the necessary changes that have occurred on Earth

duringoriginoflife.

• distinguishbetweenatomosphereofancientandpresentEarth

• analiysetheimportanceoforganicevolution

• understandthetheoriesonorganicevolution

Youhavebynowbecomefamiliarwiththeideathatalargenumberandvarietyoflivingorganismsareexistingonthisearth.Whatisthereasonbehindthisvariety?Weretheypresentrightfromthetimeoforiginofearth?Youhavealreadylearntthatearthwasformedabout4.8billionyearsagoandthefirstformoflifeappearedonlyabout3.8billionyearsago.

WhatchangesmusthaveoccurredonEarthleadingtotheformationoflife?Whatchangesmusthaveoccurredinlivingorganismstomakethemmore andmore complex? Let us try to find answers to suchinterestingquestionsinthischapter.

WhentheEarthwasformedabout4.8billionsofyearsago,itwasahotrevolvingballofgas.TheextremelyhightemperatureandthedryclimateoftheearliestEarthwouldhavemadeitimpossibleforlifetoappearandexist.Itisnowfairlyclearastowhatitmeanstobe‘alive’or‘living’.However,itisnotclearasto‘howlifefirstoriginated’.Withthe pieces of evidence available, scientists have traced the possiblechainofeventswhichmighthavetakenplaceonEarthinthelast1to4billionsofyears.

YouwillrecallthatitwasLouisPasteurwhoconductedthefamous‘swan necked flask’experiments.Withthisheprovedbeyonddoubtthatallformsoflifeariseonlyfrompreexistinglife.However,onequestionstill remainedunansweredHowdid the first form of life appear onEarth?Theanswertothisquestioncameintheformofatheory,calledtheory of chemical evolution.ThistheorywasproposedbyOparinandHaldaneindependently.Thetheoryassumesthat• theEarth’ssurfaceandatmosphereduringthefirstbillionyearsof

itsexistence,wereradicallydifferentfromthoseoftodaysconditions.

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• theprimitiveearth’satmospheredidnothaveoxygen.• thefirstlifearosefromaseriesofchemicalreactions.• solarradiation,ultravioletraysandlightning,musthavebeenthe

chiefsourcesofenergyforthesechemicalreactions.

Fig23.1EarlyEarth

IntheinitialdaysofEarth’sformation,heavyelementssuchasironandnickel,werepresentinthecentreoftheEarth.Comparativelylighteroneslikealuminiumandsiliconformedthemiddlelayer.Elementslikehydrogen,oxygenandcarbonwerefoundintheoutermostlayer.Duetothehightemperature,theatomsoftheseelementscouldnotcombinetoformmolecules.AstheEarthstartedcoolinggradually,theatomsstartedcombiningtoformmolecules.

As cooling of the Earth continued for thousands of years, theatomsofdifferentelementscombinedtogetheratrandom.Thisledtotheformationofmolecules.Theearliestmoleculesformedwerethoseofhydrogen (H2), nitrogen (N2) ammonia (NH3)methane (CH4) carbondioxide (CO2)andwatervapour (H2O).Thesecompounds formedthebasicmoleculesfortheoriginoflife.Evenmolecularoxygen(O2)isfoundtohavebeenformed.Butitprobablycombinedwithotherelements,likecarbon,hydrogen,aluminium,irontoformtheirrespectiveoxides.Hence,itisthoughtthattheearlyatmospheredidnotcontainmolecularoxygen.

It is assumed thatwater vapour formed the cloudswhich thenresultedincontinuousrainfallforhundredsofyears.Therainwaterissaidtohavefilledthehollowsandbasinsonthesurfaceoftheearthtoformoceans.Withfurthercoolingoftheearth,theinorganicmoleculescombinedwithoneanothertoformsimpleorganiccompounds.Simplesugars, fatty acids, glycerol, aminoacids and nitrogen baseswere

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presumedtohavebeenformedatthisstage.Thesechangestookplacein the presence of high amount of energy provided by discharge ofelectricalchargesduetolightningandultravioletrays.

As the earth cooled further, these compounds combined amongthemselvestoformcomplexcompounds.Haldanesuggestedthatduetotheaccumulationofthecomplexorganicmolecules,theseawaterultimatelybecameasortofa‘hot dilute soup’.Inthissoup,moleculesinteractedandaggregatedtoformmorecomplexmolecules.

It is presumed that aggregates of largemolecules formed largesizedparticlesduetotheforceactingbetweentheirmolecules.Theseaggregateshavebeencalledcoacervates.Duetotheiraffinitytowardswatermolecules,anenvelopeofwatermoleculesissaidtohaveformedaroundeach.Thisissaidtohaveincreasedthechancesofchemicalreactions.

Graduallybreakingdownand

Fig23.2Earth

buildingupofchemicalsubstancesstarted.Thecoacervatesprobablynotonlyexhibitedgrowth,butalsostartedmultiplying.Thecoacervatescontinued to constantly take innewmaterialsfromtheoceanandrelease the degradedmaterials.Thus, they exhibited the basicproper t i es o f l i f e such asmetabo l i sm , g rowth andreproduction.Gradually,groupofcomplex organic compounds,nucleicacidsaresaidtohavetakenprecisecontrolofthecoacervates.This led to the establishment ofnucleic acids as the geneticmaterial. In course of time, thecoacervatesbecameestablishedintothefirstlivingsystemswhichhavebeennamedprotobionts.Someoftheproteinsintheprotobiontsaresaidtohavedevelopedtheabilitytospeedupthechemicalreactions,therebyfunctioningasthefirstenzymes.

Inthecourseoftimeprotobiontsbecameenclosedinaproteinlipidmembrane.Thispropertyimprovedtheirsurvivalability.Metabolism,growthandreproductionbecameregular,preciseandcontrolled,leadingtotheformationoffirstcells.

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The first forms of life developed in the oxygen-free atmosphere.Hence,itisbelievedthattheseprimitiveformsoflifeobtainedenergybythefermentationoforganiccompounds.Recallanaerobicrespiration,which you have read in chapter 20. Theywere thus, heterotrophsrequiringreadymadeorganiccompoundsasfood.

Autotrophsaresaidtohavearisenmuchlaterintheprimitiveearth.Theappearanceofautotrophsintheformofbluegreenalgae,changedthesituationonearth.Theseorganismsreleasedfreemolecularoxygenintotheatmosphere,graduallytransformingitintoanoxidizingtype.

The followingtablesummarises thesequenceofeventsonearthleadingtotheappearanceoflife.

table 23.1 events on earth leading to the appearance of life.

Changesintime

4.8Billionyearsago

3.8Billion

Yearsago

2.5BillionYearsago

Present

Radiation Highuv uvlight Lessuvlight verylowlevelofuvlight

ConstitiuentsofAtmosphere

H2,CH4,H2ONH3,CO2,N2,

NH3,H2O,H2,CO2,N2

O3,O2,CO2,H2O,H2,N2

Molecules SimpleMolecules

Complex

Molecules

Organic

molecules

Producedbycells

Cell/Lifeforms

None None Protobionts Presentdayforms

organic evolutionTheprimitivecellsthatresultedfromchemicalevolution,gradually

gaverisetoorganismssuchasbacteria,algae,fungiandprotozoans.These organisms in turn, gave rise to a variety of life forms that areexistingtodayontheearth.Thiswaspossibleduetotheslowandgradualprocessbywhich livingorganismshaveundergonechangesfrom the single celled forms to the many celled forms of life.

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This slow and gradual process of change is known asorganic evolution.Theprocessistheresultofinnumerablemodificationswhich

Fig23.3MajoreventsinthehistoryofLife

the organisms have developed under theinfluence of their environment. Thesechangeshavebeenpassedonfromgenerationto generation bringing about formation ofnewvarietieswithinandacrossspecies.

Theoccurrenceofevolutionissupportedby the innumerable direct and indirectevidencesthatwecangatherfromorganismsof the past and present. Themechanismof organic evolution, has been explainedby ideasput forthbyscientists fromtimetotime.Theseideascametobeknownastheoriesinorganicevolution.Followingaresomeofthetheoriesthattrytoexplainthemechanismoforganicevolution.

Lamarckism

One of the earliest ideas on organicevolutionwasproposedbyaFrenchZoologistbynameJeanBaptisteLamarck.In1809,he proposed a theory, which came to bepopularlyknownas‘Theoryofinheritanceofacquiredcharacters’.Itisalsodescribedas ‘Lamarckism’. The theory isbasedonthreemainideasnew needs, use and disuse of organs and inheritance of acquired characters.

• Environment is highly unstable and is subject to frequent changes.Lamarckbelievedthatsuchchangescreatenewneedsintheorganisms.Iftheorganismsfailtomakenecessarychangesfavourably,itcannotsurvive.

• The appearance of newneeds forces the organism to put in additionaleffortstofulfilltheneeds.Itmayputparticularpartof

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itsbodyintomoreandmorefrequentuse.Similarlyitmayalsobenecessaryfortheorganismtoputapartofitsbodyintolessuseormaynotuseitall.Thisideacametobeknownasuseanddisuseoforgans.Anypartofthebodythatismoreandmoreused,islikelytogrowlargerandbecomebetterandstronger.Inthesamewayanypartofthebodywhichislessfrequentlyused,hasatendencytobecomelessprominentandmayevenultimatelydisappear.Thus,byadifferentialoveruseanddisuseofvariousbodyparts,anorganismwouldchangetosomeextentandacquirenewcharacters.

• Lamarckbelievedthatsuchcharactersacquiredbyanorganismgettransmittedtothefuturegenerations.Ineverygeneration,freshcharactersareacquired.

Asaresult,aftermanygenerationsthechangesaccumulateandthespeciesbecomemodifiedintoanewone.Lamarck’sideasonevolutionmaybeexplainedbycitingafewexamplesfromhisownwritings.

The exampleof giraffe is cited in support of the ideaof overuseofbodyparts.Amongmammals,youknowthatgiraffeispeculiarinhavingalongneckandlongerforelimbsLamarck.suggestedthattheancestorsofgiraffeswereassmallasdeer.Theavailabilityofgrassandothersmallplantswasdepleting.Thiswasduetoseverecompetitionfromotherherbivoresanddrought.Lamarcksuggested thatgiraffesstartedstretchingtheirneckandforelimbsinordertoreachtheleavesoftallerplants.Thiscontinuedforseveralgenerationsandasaresult,neckbecamelonger,asalsotheforelimbs.

Fig23.4Lamarck’stheoryofuseanddisuseofparts

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TheabsenceoflimbsinsnakeswasinterpretedbyLamarckasanevolutionarychange.Hesuggestedthatancestorsofsnakeshadfourwelldevelopedlimbs.Snakeswerehuntedbymoreadvancedgroupofanimalssuchasbirdsandmammals.Inordertosurvive,theystartedcrawlingonthegroundandspentmostoftheirtimehidingincrevicesandholes.Thus, they starteddisusing their limbs.This resulted inthelimbsbecomingdegenerateandultimatelydisappear.Thelimblessconditionwaspassedontosubsequentgenerations.

Lamarck’sideashadsomedrawbacks.Histheorycannotexplainhowbodycellspassontheacquiredcharacteristicstoreproductivecells.Experimentshaveshownthatacquiredcharactersarenotinheritedandinheritedcharactersarenotacquired.

CharlesDarwin

darwinism Charles darwin proposed a theory in 1859 toexplain the possiblemechanism of evolution.This theory came to be known as a theory of natural selection.Itismorepopularlyknownas‘Darwinism’.Thistheoryisbasedonthefollowingprinciples.

Darwinfoundaninterestingfeatureinallorganisms.Allorganismshaveanaturalcapacitytoproducealargenumberofyoungones.Hecalledthiscapacityas‘overproduction’.Darwingavemanyexamplestosupportthisidea.

Elephantsaretheslowestreproducinganimals. Ina lifespanofabout90years,apairofelephantsmayproduceamaximumofsixyoungones.Darwincalculatedthatifallthesixyoungonessurvive,growandreproduceatthesamerate,therewouldbe19millionelephantsinjustabout750years.Inspiteofsuchanenormousrateofreproductionthenumberof individuals ineachspecies remainsnearlyconstantoverlongperiodsoftime.

• darwin reasoned that, as a result of high rate of reproduction,theremustbeacompetitionbetweenindividuals.Itisforsharingfoodwater,livingspaceandotherresources.ThiscompetitionwasdescribedbyDarwinas‘struggle for existence’.

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• He found that generally the young ones of an organism showdifferencescomparedtotheparent.Hedescribedthedifferencesas‘variations’.Theyaretheruleofnature.Theyhelpanorganismtoadjustbettertotheenvironment.

• Darwin believed that nature selects only those organismswhichhavefavourablevariations.Theycontinuetoproduceyoungoneswiththesevariations.Thisprovidesadvantagestosuchorganisms.Darwindescribedthisprocessas‘natural selection’.

• Darwinpresumedthatonlythoseorganismswhichhavedevelopedadvantageousvariationshaveabetterchanceofsurvival.Thelessadaptedandthenotadaptedorganismsgeteliminated.Thisideacametobeknownas‘survival of the fittest’.Thus,newspeciesdevelop fromtheexistingones inaslowand

gradualway.

Darwin believed thatwhile variations are the rawmaterials forevolution, natural selection is the operating force.However,Darwinfailedtorecongnizethesourceofvariationsintheorganisms.Hencegoesthecommonsaying,‘Darwin explained the survival of fittest, but not their arrival’.Hehadnoideaofthemechanismofinheritance.

VictorHugoDevries in 1902 proposed the idea that variationsarebroughtaboutbysuddenchangestothegeneticmakeupofanorganism.Suchchangesarecalledmutations.Themoderntheoryonorganicevolutionisthesynthesisofideasfromthetheoryofnaturalselectionandthemutationtheory.Thesetheorieshavebeenexaminedinthelightofpresentknowledgeonhowmutationsoccur.Itisknownasneodarwinism.

exercises:i. Four allternatives are given to each of the following incomplete statement / question. Choose the right answer

1. Theterm‘hotdilutesoup’,wasusedby

a.Oparin b.Darwin c.Haldane d.Pasteur

2. Whichgaswasabsentintheatmosphereatthetimeoforiginoflife?

a.ammonia b.hydrogen c.oxygen d.methane

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3. Thefirstorganismsonprimitiveearthwere

a.autotrophic b.heterotrophicandanaerobic

c.parasitic d.prokaryoticandautotrophic

4. ThegreatestweaknessinDarwin’stheorywashisfailuretoexplain

a.overproduction b.survivalofthefittest

c.struggleforexistence d.variations

ii. Fill in the blanks with suitable words :1. Earthwasahotrevolvingballof____________about4.8billionsof

yearsago.

2. Lightestelementhydrogenwasfoundinthe____________layeroftheearliestearth.

3. Variationscausedbysuddengeneticchangesarecalled__________.

4. Darwinexplainedthesurvivalofthefittest,butnottheir__________.

iii. match the following : A B1.Lamarck a.neodarwinism

2.Darwin b.mutationtheory

3.HugoDevries c.theoryofnaturalselection

4.Oparin d.theoryofinheritanceofacquiredcharacters

e.theoryofchemicalevolution

iV. answer the following :1. Whatisorganicevolution?

2. ExplainLamarck’stheoryofuseanddisuseoforganswithsuitableexamples.

3 Whatistheroleofvariationsinevolution?

4. Whatismutation?

5. Whatisneodarwinism?

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Chapter 24

Beyond the earthafter studying this chapter students :

• definethetermcelestialsphere.

• distinguish between Geocentric and Heliocentric models of solarsystem.

• listthemembersofthesolarsystem.

• statethemainfeaturesofmoon.

• statetheplanetsintheorderofincreasingdistancefromthesun.

• locate the planets Mercury, Mars, Venus, Jupiter and Saturnwithoutthehelpoftelescopes.

• distinguishbetweenstarsandplanets.

• explainthemainfeaturesoftheplanets.

• recognisefamiliarconstellations.

• namethezodiacalconstellations.

• describethecontributionofsomepersonalitiesassociatedwiththestudyofcelestialobjects.

Solar system

Haveyouobservedthenightskyonacloudlessday?Ifyouspendsometimewatchingityouwillreallyenjoy.Thepatternsintheskyhaveinspiredmanydesignmakersandpoetstoo.Clearmoonlessnightinaplaceawayfromthecity,isbestforwatchingthesky.Evenotherwiseitisagoodexperiencetowatchit.

Youmaynoticemoonandthousandsoftwinklingstarswhichareunevenlydistributed.Youseemanyrecognizablepatternsofstars.Ifyouobservecarefullyyoumayalsoseeshiningstarlikeobjectswhichdonottwinkle.Occasionallyyoumayseestreaksoflightwhichgivestheimpressionoffallingstars.

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Theseobjectsappeartobelocatedonahugesphere.Youappeartobeatitscentre.ThissphereiscalledCelestialSphere.Whatcouldbetheradiusofsuchasphere?Objectsincelestialspherearecalledcelestialobjects.

Fig24.1Celestial sphere

DirectobservationsshowthatmostofthecelestialobjectsappeartomovefromEasttoWest.Thisobservationmademanypeoplethinkthatweareatthecentreoftheuniverseandallothercelestialobjectsaremovingaroundus.Basedontheseobservationspeopledevelopedamodel.Inthismodelearthisconsideredascentreoftheuniverseandallothercelestialobjectsmovingaroundus.Themodel ispopularlycalled ‘Geocentricmodel’.Greek philosopher Aristotle, Ptolemy andmanyotherphilosophersbelievedinthissystem.Basedongeocentricmodelitwasnotpossibletoexplainmanyeventslikesolareclipsesandthevariationsinthepathofplanets.

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Nicholas Copernicus, proposed an alternative model called‘Heliocentric’model.HeplacedtheSunatthecentreoftheobservableuniverseandallothercelestialobjectsincludingtheearthasobjectsmovingaroundtheSun.JohannesKeplerandGalileoGalileprovidedscientific evidences for thismodel. Indian astronomers “NeelakantaSomasatvan(Somayaji)”basedonasuggestionof“Parameshwara”hadproposedamodelsimilarto‘Heliocentric’systemearlier.Developmentoftelescopeandmathematicalcalculationsbasedongravitationallaws,helpedinbetterunderstandingof‘Heliocentricmodel’.

Note : Heliocentricmodelhasalsoundergone changes.Youwill learnaboutitinhigherclasses.

Let us know about somemembers ofHeliocentricmodel. Solarsystemisasmallpartoftheentireuniverse.SolarsystemhasonestarthatisSunasthecentreandthememberslikeplanets,movingaroundit.Solarsystemasweunderstandtoday,comprisesofthefollowing

• TheSunwhichisthecentreofthesolarsystem

• EightplanetsareMercury,Venus,Earth,Mars,Jupiter,Saturn,UranusandNeptune

• TheAsteroidbeltbetweentheorbitsofMarsandJupiter

• Satellitesoftheplanets,whicharealsocalledthemoonsoftheplanets.

• CometssuchasHalley.

• Artificialsatellitesandspacecrafts.

Sun

Sunisthecentreofthesolarsystem.Ithasaradiusof109timesthat of the earth. Itmainly consists ofHydrogen andHelium. Thereactionsinthesunreleaseenormousamountofenergy.Apartoftheenergyisreceivedbytheearthintheformofheatandlight.Lifeonearthissustainedbythisenergy.YouwillstudymoreaboutSuninthehigherclasses

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Know this : Thesunlightthatyouareseeingrightnowhasleftthesunabout8½minutesago.Thatmeansitis8½minutesold.Thevelocityoflightis300000kmpersecond.Thedistancebetweenearthandsunisthereforeabout8½×60×300000=150millionkm=1.5×1011m

planets Planetsappearasshiningobjects.Sometimestheyaremistaken

forstars.Amongsomanystarsandplanets,howcanyourecognizeaplanet?Starstwinklebutplanetsdonot.Why?Thispropertyhelpsyoutodistinguishbetweenastarandaplanet.Starsareselfluminous,planetsarenot.Planetsreflectsunlightandappearbright.Starshaveverylargesizewhencomparedtotheplanets.Theyappearsmallbecauseoftheirlongdistancefromtheearth.Wecanobserveonlyfourplanetseasilywithoutatelescope.TheyareVenus,Mars,JupiterandSaturn.YoumayobserveanotherplanetMercuryjustbeforesunriseandjustaftersunsetiftheskyisclear.

Weshallstudyaboutmembersofsolarsystemintheorderoftheirdistancefromthesun.

Fig24.2Planetsinoursolarsystem

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period of rotation:Timetakenbyaplanetorsatellitetorotateoncearounditsownaxis.

period of revolution:Timetakenbyamemberofthesolarsystemtogoaroundthesunonce.

Mercury

Fig24.3Mercury

Mercuryisthenearestplanettothesun.SunrisesorsetswithinabouttwohoursofMercury’srisingorsetting.Youcanspot itat theplaceof sunriseorsunset, early in themorning or soonafterthesunset.Butitisdifficulttogeta good view. Mercury has heavilycratered surface (see the fig.24.3)Surfacetemperaturevariesfrom4270Cto-1830C.Itsspecificgravityis0.99.Its period of rotation and period ofrevolution are 59 days and 88 daysrespectively.

Venus

Venusisthesecondplanet.Itcanbe

Fig24.4Venus

recognizedeasily.Itsatmosphereismadeupofmostlycarbondioxide.SunriseandSunsetasseenfromtheplanetwillbe in theWestandEastdirectionrespectively.Canyougive reason for this?. Its period ofrotationis243daysandtakes224daystogoaroundthesunonce.ItmeansadayonVenusislongerthanitsyear.

Whatisthedurationofdayandyearonearth?Compare thespeedof rotation of Earth and speed of rotation of Venus.What is yourconclusion?

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The surface temperature of Venus should be less than that ofMercuryconsideringitsdistancefromtheSun.ButitiscomparabletoMercury.It isabout4000C.This isduetogreenhouseeffectorwarmingoftheearthincommonlanguage.Carbondioxideblockslongwavelengthinfraredradiationsandheatistrappedinside.ThespecificgravityofVenusis0.95.

Activity 24.1

observe the sky at around sunset. In the western direction above the hori-zon you will notice a bright shining celestial object. It is the first object that you can see in the western sky before the cover of darkness. It is Venus. You can see it in eastern sky much before sunrise. People call it morning star or evening star though it is a planet.

earth

Earthisthethirdplanetfromthesun.Earthhasoneknownnaturalsatellite,themoon.Earthistheonlyplanetinthesolarsystemonwhichlifeisknowntoexist.Whatmakesearthsospecial?Whichfactorshelplifetooriginate,evolveanddevelop?Severalconditionsarenecessarytoco-existforthis.Canyoulistthem?

Think : Isthereanykindoflifeexistinginanyothercelestialbody?Attemptsarebeingmadetofindananswerforthisquestion.OnesuchprogrammeisSETI:SEARCHforEXTRATERRESTRIALINTELLIGENCE.

Nearlytwothirdsoftheearth’ssurfaceiscoveredwithwater.Earthhasanatmospherewhichextendstoaheightofafewhundredsofkilometres,thoughwecannotexactlydefineitsboundary.Thelayersofatmospherecontainnitrogen,oxygen,carbondioxide,watervapourandsmallquantitiesofothergases.

Moon

Whenwetalkaboutmoonmanytimeswebecomepoetic.Manysongs andmany poems arewritten by the inspiration of differentphasesofmoon.Itappearsasabigbrightcelestialbodyduringfullmoondaywhicharousescuriosity.Youmighthaveseenitmanytimes

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during day time also. It is the only knownnatural satellite of theEarth.Therearehugecratersonmoon.Ithasnoatmosphere.Indiaexploredthissatellitebyitsprogrammecalled“ChandrayanaI”intheyear2009.EarlierAmericaundertookahistoricmission.OnJuly21,1969AmericanastronautNeilArmstronglandedontheMoon.HewasfollowedbyEdwinAldrin.

Fig24.5CratersonmoonFig24.6Apollo

Howdidthetwotalktoeachotherwhenthereisnoairforsoundtotravel?Howdidtheygetoxygen?

Recall : Drawpicturesofdifferentphasesofmoonwhichyouhavestudiedinearlierclasses

Mars

Marsisthefourthplanet.Itisareddishplanet.SpacecraftslikeVikinghaveexploredMars,forevidenceoflife.

Someplacesinmarshavemoderaterangeoftemperature.Ithasoxygen,nitrogenandwater.Ithasfrozencarbondioxidenearthepoleswhichlooklikecaps.Itisthepresenceofthesefactorsthatmadeustothinkabouttheexistenceofsomeformof lifeonMars.MarshastwonaturalsatellitesPhobosandDeimos.ThespecificgravityofMarsis0.72.Thesurfacetemperaturevariesfromlessthan00Cto250CPeriodofrotationofmarsisabout24

21 hours.Itsperiodofrevolution

is687days.

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Fig24.7Mars Fig24.8RoveronMars

asteroids and Meteoroids

BetweenthevastspaceoftheorbitsofMarsandJupitertherearethousandsofirregularshapedlumpsofrocksthatorbittheSun.Theyareasteroids.Someasteroidsarealsofoundinotherpartsofthesolarsystem.ButthemainasteroidbeltisbetweentheorbitsofMarsandJupiter.ThelargestasteroidsareCeres,Pallas,JunoandVesta.

Meteoroidsarechunksofmatterwhichmayoriginatefromasteroidbelt.Sometimestheymayentertheearth’satmosphereandburnupdue to theheatgeneratedby friction.Thesemeteoroidswhichburncompletelyarecalled‘meteors’whichwecallshootingstars.Theyarealsocalledfallingstars.Ifalargenumberofthemintheskyhappentoappearatthesametime,theycauseashowerofmeteors.Duringthevisitofacometsomefragmentsofthecometburnupafterenteringtheearth’satmosphere.Biggermeteoroidssometimessurvivethejourneyandhittheearthresultingincratersandventsontheearth’scrust.Theyarecalledmeteorites.Manyplanets,satelliteshavelargecratersformedbytheimpactofmeteorites.

Leonid showers

SomewherearoundthemidNovemberintheconstellationLeothatisinNorth-Eastdirectionifyouwatchtheskyaftermidnightyoumayobservemorenumberofmeteors.

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Jupiter

Fig24.9Jupiter(Guru,Brahaspathi)

Jupiter is thefifthplanet. Itisthebiggestplanetofthesolarsystem. Its Orbital period isnearly12years.Itsdayisabout10hours.Thatmeansitrotatesvery fast. Due to fast rotationit is bulged at the equator andflattenedatthepoles.Thethickgas cloudswhich are attachedto the planet due to its stronggravitationalforcealsorotatewiththe planet resulting in bands.Thesebandsarevisiblethrougha telescope. Try to identify thisplanetinnightsky.

ThespecificgravityofJupiteris0.24.Jupiterisfarawayfromthesun.Canyouimagineitssurfacetemperature?

Galileoidentifiedfoursatellites

Fig24.10Jupiteranditsfourlargesatellites

of Jupiter using a telescopepreparedbyhimself.TheyareIo,Europa,GanymedeandCallisto.TherearemanyothersatellitesofJupiter. Io is an interestingsatellite because it has activevolcanoes. Voyager space craftdiscoveredaringsystemaroundthe planet. Jupiter emits radiosignals.

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Saturn

Fig24.11Saturnanditsringlets

Saturnisthesixthplanet.Itisthesecondbiggestplanet.Itisamostfascinatingexperiencetoviewthisplanetusingatelescope.Itsspecial feature isprominentringsystem.Theringsystemismadeupofmanysmallringlets.Theringletsaremadeupoficymatter.Itsspecificgravityislessthan that of water. You canimagine a piece of the planetSaturnfloatingonwater.Ithas

manysatellitesamongwhichTitanisofspecialinterest.Itistheonlynaturalsatellitewhichhas itsownatmosphere in thesolarsystem.Saturnhasspecificgravityof0.13.Itisthelowestwhencomparedtootherplanets.Itsperiodofrotationandrevolutionare10hrs15minutesand29.46yearsrespectively.

Uranus

Uranusistheseventhplanetanditisthe

Fig24.12Uranus

thirdlargestplanet.AringsystemaroundthisplanetwasdiscoveredbyProf.J.C.Bhattacharyaand K.Kuppuswamy of Indian Institute ofAstrophysicsBangalore. The planetwas firstdiscoveredbyWilliamHerschel.Itisapeculiarplanetinthesensethatitsaxisofrotationhasatiltofabout820.ExceptVenusalltheplanetsrotatefromwesttoeastwithsometilt.Uranushas a specific gravity of 0.29. Its period ofrotationandrevolutionare13hoursand84.02yearsrespectively.Thisplanetappearstorotateonverticalaxis.Comparethistothetiltoftheearth.

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AglobewillhelpyoutocomparetheaxisofrotationofUranuswiththeaxisofrotationoftheearth.

Know this : You have seen the models of globes .You might havewonderedwhythemodeloftheearthisinclinedinsteadofbeingstraight.What might be the reason? Can you imagine the model of uranus ?

neptune :

Fig24.13Neptune

Neptuneistheeighthplanet.TheplanetNeptunecanbeseenonlywiththehelpofa telescope. Earlier its existence waspredicted bymathematical calculations.Its specific gravity is 0.3. Its period ofrotation and revolution are 18 hrs 30minutesand164.81yearsrespectively.

pluto

EarlierPlutowasconsideredasaplanetof

Fig24.14Pluto

the solar system. But in 2006 theInternationalAstronomicalUnion (IAU)adoptedanewdefinitionofaplanetandaccordingtothisPlutodoesnotqualifyasaplanetofthesolarsystem.Howeveritcontinuestobeamember,ofthesolarsystem.Itisalsocalleddwarfplanet.

Activity 24.2Find out the reasons for removing Pluto from the list of planets.

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Comets Cometsareguestsofthesolarsysteminthesensethattheyhave

verylongorbitalperiodsandappearrarely.

Majorconstituentsofnucleusofacometaresilicatesandmattermadeupoffrozengases.

Cometsaresphericalinshape.WhentheycomeneartheSuntheydevelop tails.Why?Theybecome visiblewhen they are close to the

Fig24.15Comet

sunandearth.Manyastronomershavethehabitofwatchingcometsthrough their telescope andstudying their orbital period.Many comets are named aftertheirdiscoverers.OnesuchcometisHalley’s cometwhich can beseenoncein76years.Itwaslastseenin1986.Whenisitlikelytobeseennext?Activity 24.3

Collect information about the different comets that have appeared in the past 60 to 70 years.

Superstitions about the Comets

Some people think that comets are messengers of disasters, such aswars, epidemics andfloods.But these are allmythsand superstitions.Appearanceofacometisanaturalphenomenon.Wehavenoreasontobeafraidofit.

Canweaddnewmemberstosolar

Fig24.16Artificialsatellite

system?Inadditiontothenaturalsatellite moon, we have addedmanysmallermoonsintheformof artificial satellites which areuseful tous inmanyways.Canyoulisttheiruses?

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Stars Apartfrommembersofthesolarsystemtherearecelestialobjects

which ariseourcuriosity.Letusstudyabout them.Youseemanytwinklingcelestialobjectsinthenightsky.Thesearestars.Theyappeartobeatthesamedistance.Why?

Sunistheneareststartous.Youknowthatlighttakesabout8½minutestoreachtheearthfromthesun.

Thelightfromthestarsofthenightskytakesyearstoreachtheearth.Imaginewhatmightbetheirdistance!Theymustbequitehuge.Thedistanceofstarsisusuallyexpressedintermsofaunitcalledlightyear.Onelightyearisthedistancetravelledbylightinoneyear.Thisisequalto365×24×60×60×300000km.ConsiderthestarSirius.Itisthebrighteststarinthenightsky.Itisabout8.7lightyearsaway.Thatmeanswhenyoulookatit,thelightthatentersyoureyehasleftthestar8.7yearsago.

Youobservestarsofdifferentcolours.Theyhaveyellow,orange,white,redandbluecolour.Howaretemperatureandcolourrelated?

Activity 24.4

Heat an iron wire with insulated handle. First it becomes red. When heating is continued it turns into orange yellow and whitish in colour before it melts down.

Activity 24.5

Observe the blue flames of a LPG stove when it is being used. Also observe the change in colour of the blue flames when water drops get sprinkled on the flame. Can you give reason for change in colours?

Relativelyred,orange,yellow,whiteandbluecoloursindicatetheincreasingorderoftemperatureofstars.

Star patterns in the sky Whenyoulookatthestars inthenightskyyouobservecertain

patterns.Thepatternsremainunchangedoveraperiodoftime.Peopleimagined some objects, animals,mythological characters formedbyjoiningthepositionsofstars.Theregionaroundrecognisablepatternofagroupofstarsiscalledaconstellation.Theskyisdividedinto88constellationregions.Eachregionisnamedafterthatconstellation.ForexamplegroupofsevenstarsintheNorthiscalledSaptharshiMandalaorBigBearorUrsaMajor.

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UrsaMajorwithsevenstarsmovesaroundthepolestar.YoumayseeitinthemorningofwinterseasoninKarnataka.

Fig24.17Ursamajorconstellationswithpolestar

Note : Realappearancewillbethedots.Thelinesdrawnareimaginary.

ConstellationCassiopeiainnorthernregionoftheskycanbeusedtolocatethepositionofpolestarduringearlynightofwinterseason.

Know this : Apart from using Mariners’ Compass there are differentmethodsoffindingthedirections.OnesuchmethodislocatingpolestarandalsoidentifyingthelocationsofConstellations.Italsohelpstoknowtheapproximatetime,month.SomeeasilyidentifiableconstellationsareUrsaMajor,Orion,Cassiopeia,LeoMajor.

Fig24.18Afewconstellations

Cassiopeia

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Orionisthemosteasilyrecognizedconstellationinwinterseason.Itsmovementcanbeeasilymonitored.Thisconstellationhasredcolouredstarbetelgeuse.IthasalsobluecolouredstarRigel.ItcanleadtothelocationoftheStarSirius,whenastraightlineisdrawnfromthebeltconsistingofthreestarsinthestraightline.Referthediagram.

Zodiac

Themovement of the sun, the planets and themoon appear tofollowapathfromeasttowest.ThisapparentpathiscalledZodiacbelt.TwelveconstellationswhicharelocatedinthispatharecalledZodiacalconstellations.

1. Aries(Mesha)

Fig24.1912Zodiacalconstellations

2. Taurus(Vrishabha)

3. Gemini(Mithuna)

4. Cancer(Karka)

5. Leo(Simha)

6. Virgo(Kanya)

7. Libra(Tula)

8. Scorpius(Vrischika)

9. Sagittarius(Dhanu)

10.Capricornus(Makara)

11.Aquarius(Kumbha)

12.Pisces(meera)

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Contrarytothepopularbeliefof12zodiacalconstellations,thereis 13th Zodiacal constellation. Its name isOphiuchus. It is a largeconstellation located around celestial equator.Other name of thisconstellationisserpentariusmeaningSerpent-Bearer.

Ourcuriositytounderstandmoreaboutstarsleadsustogalaxiesandstagesoflifecycleofastar.Youwillstudyabouttheminhigherclasses.

Extended Activity 24.6

Make your own planetarium and also visit a planetarium.

1.Takeacheapopaqueflatbottomplasticbowl.Pastewhitepaperontheflatsurface.MarktheconstellationUrsaMajororOriononit.Withasharppin,pierceholesatthebottomoftheplasticbowlonthestarsoftheconstellation.Apowerfullampwithdiffusedlight(Filamentlamps shouldnot beused; otherwise pinhole camera effectwill befound)likeLEDlampshouldbeplacedinside.Inadarkroomprojecttheholesontheroofoftheroom.Youwillseetheconstellation.Ifyouuseabiggerbowlwithmanyconstellationsmarkedasholesyoucanrotateitandobservethemovement.

exercises :

I. Four alternatives are given to each of the following incomplete statement / question. Choose the right answer :

I. Theconstellationthathelpstolocatenorthstaris,

a.Cassiopia b.Orion c.Taurus d.Leo

2. Thesecondbiggestplanetofthesolarsystemhas,

a. lowestdensity b.densityequaltowater

c. highestdensity d.densityequaltoearth

3. Thepolesofthisplanetfacesthesunforlongerperiodsoftimethananyotherplanet.

a. Mars b.Uranusc.Jupiter d.Saturn

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4. Polaricecapsoftheplanetmarsaredueto,

a.solidifiedwater

b.solidifiedcarbondioxide

c.volcanoe’seruptednearthepoles

d.coverofdustparticlesthatreflectlight.

5. Heatwavesaretrappedtomaximumextentintheplanet,

a.Mercuryb.Venus c.Earth d.Neptune,

II. Fill in the blanks with suitable words

1. Radiosignalsareemittedbytheplanet_____________________.

2. ThecolouroftheplanetMarsis__________________________.

3. Winterseasonconstellationis___________________________.

4. Asteroidsaremainlyfoundbetweentheorbitsof______________.

5. Ultravioletraysfromthesuncanbefilteredbytheearth’satmosphericlayercalled______________________________.

III. Match the following :

A B

1.highlytiltedplanet a.earth

2.satelliteofJupiter b.titan

3.constellation c.halley

4.thirdPlanetfromthesun d.Io

e.uranus

f.ursaMajor

g.sirius

IV. answer the following :

1. Whichplanetiscalledmorningoreveningstar?

2. Whichplanetwasremovedfromthelistof9planetsin2006?

3. Expressthefollowinginkm

a.10lightminutesb.10lightdaysc.10lightyears.

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4. Namethefollowing:

a.Mostfascinatingplanetwithsetofringsystemasviewedfromatelescope

b.Nearestplanettotheearth c.Nearestplanettothesun

d.BiggestplanetoftheSolarSystem

5. WhydoCometsdeveloptailsastheyapproachthesun?

6. Howaresatellitesdifferentfromplanets?

7. Whichsatellitehasactivevolcanoes?

8. Givereasonforthefollowing:

a. A person in England can recognize the pole star easily than apersoninBangalore.

b.Mercuryisdifficulttoobserve

c.AdayonVenusislongerthanitsyear

d.GreenhouseeffectisprominentonVenus.

V. State true or false :

1. Saturnhasthehighestdensity

2. Venuscanbeseenoverheadinthenightsky.

3. Aries(Mesha)isaZodiacalconstellation

4. Marscontainsoxygeninitsatmosphere

5. Moonhasnoatmosphere

6. TitanisasatelliteofJupiter

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FORQUICKGLA

NCE

Sl.

No.

Plan

ets

Diameter

Yearin

Earth

Time

Dayin

Earth

Time

MainGasesin

atmoshere

Number

ofNatural

moons

Mainfeatures

Average

distan

ceof

plan

etsfrom

sunin

million

km1

Mercury

4878

Km

88days

59days

Tracesof

Argon

,Neon,

Helium

0Daytim

e temperatu

e 8800

F(470

0C);nighttim

e-300

0F(-

1830

C)

58

2Venus

1210

2Km

224days,1

7hrs

243d

ays

Carbon

diaxide(very

thick)

0Rotateseast tow

est instead of

westtoeast,asotherplanetsdo

107

3Earth

1.27

56Km

365days,6

hrs

1day,23

hou

rs,5

6minutes

Nitrogen,

Oxygen

1Onlybod

yk n

owntohavel ife;

mild

clim

ate,w

aterassolid,

liquid, gas

149

4Mars

6.79

2Km

687days,23hrs

24hou

rs,3

7minutes

Carbon

dioxide(thin)

2Ice-capp

edpoles,fourseason

s,

duststorm

s22

4

5Ju

piter

14.298

4Km

11years,1

1mon

ths

9hou

rs,56

minutes

Hydrogen,

Helium

atleast16

Colou

rfulbands ofgas, m

arked

bylighting,w

ithaurorasnear

poles;G

reatRedSpot isstorm

biggerthan

Earth

768

6Saturn

12.053

6Km

29years,5

mon

ths

10hou

rs,3

9minutes

Hydrogen,

Helium

atleast18

Circled

bycolourfulicerings

r angingi nwidthf rom

fingerna

ils

tohou

ses

1,42

4

7Uranus

5.11

18Km

84year

17hou

rs,1

4minutes

Hydrogen,

Helium,

Methan

e

17Tipped

sidew

ays sop

ole not

equator-facesSun

2,84

8

8Neptune

4958

2Km

164years

16hou

rs,7

minutes

Hydrogen,

Helium,

Methan

e

8Windsof 1,50

0 Kph

(930

mph

) highestrecordedonanyplan

et4,48

0,00

0

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reFerenCe BooKS

• ATextbookofPhysicsbyMaryJones,FeoffJonesandPhilip Marchington

• ATextbookofPhysicsbyLakhmirSinghandManjithKaur.

• ConciseBiologybyTaylorE.L.B.S.

• FundamentalsofBiologybyM.B.V.Roberts.E.L.B.S.

• UnderstandingEnvironment by KiranChokkar andOthers, SagePublicationsNewDelhi

• EnvironmentalStudiesFromCrisisToCurebyR.Rajagopalan OxfordUniversityPress.

• EncyclopedaBrittanica2010Edition

• Wikipediaencyclopedia

yoU Can aLSo VISIt theSe WeBSIteS

www.enwikibooks.org/wiki/highschool

www.ehow.com

www.share2learn.com

www..sciencemaste.com

www.library.thinkquest.org

www.biology.arizona.edu

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