Class 11

Biology

Chapter 6

Anatomy of flowering plants

The tissue A group of cells having a common origin and usually performing common function are called tissues.

Meristematic tissue is a simple tissue composed of group of similar and immature cells which can divide and form new cells. The meristem which occurs at tips of roots and shoots are called apical meristem.

Intercalary meristem occurs between mature tissues especially in grasses.Both apical meristems and intercalary meristems are primary meristems because they appear early in life of a plant and help to form the primary plant body.

The meristem which occurs on the sides and takes part in increasing girth of the plants are called Lateral meristem. Intrafascicular cambium in the primary lateral meristem. Vascular cambium, cork cambium are secondary meristem.

The cells that have become structurally and functionally specialized and lose the ability to divide are called permanent tissue. Permanent tissues having all cells similar in structure and function are called simple permanent tissues and those having different kinds of cells are called complex tissue.

Parenchyma is a simple permanent living tissue which is made up of thin-walled isodiametric cells. Each cell encloses a large central vacuole and peripheral cytoplasm containing nucleus. They are found in non-woody and soft

areas of stem, root, leaves, fruits and flowers. They store the food and provide turgidity to softer parts of plant.

Collenchyma consists of cells which are much thickened at corner due to cellulose, hemicellulose and pectin. Oval, spherical or polygonal often contain chlorophyll. They provide mechanical support to the growing parts of the plants like young stem.

Sclerenchymas areor no protoplasm due to deposition of cellulose or lignin. They are of two types: fibres and sclereids. They provide mechanical support to mature plant organs to tolerate bending, shear

Complex Tissues– Xylem and phloem constitute the complex tissues in plants and work together as a unit.

Xylem Phloem

1. It conducts water or

areas of stem, root, leaves, fruits and flowers. They store the food and provide turgidity to softer parts of plant.

consists of cells which are much thickened at corner due to cellulose, hemicellulose and pectin. Oval, spherical or polygonal often contain chlorophyll. They provide mechanical support to the growing parts of the plants

are supportive tissue having highly thick walled cells with little or no protoplasm due to deposition of cellulose or lignin. They are of two types: fibres and sclereids. They provide mechanical support to mature plant organs to tolerate bending, shearing, compression etc.

Xylem and phloem constitute the complex tissues in plants and work

Phloem

1. Phloem conducts organic

areas of stem, root, leaves, fruits and flowers. They store the food and provide

consists of cells which are much thickened at corner due to cellulose, hemicellulose and pectin. Oval, spherical or polygonal often contain chlorophyll. They provide mechanical support to the growing parts of the plants

supportive tissue having highly thick walled cells with little or no protoplasm due to deposition of cellulose or lignin. They are of two types: fibres and sclereids. They provide mechanical support to mature plant organs to

Xylem and phloem constitute the complex tissues in plants and work

sap.

2. Xylem is found deep in the plant.

3. Xylem provides mechanical strength.

4. is made up of vessels, tracheid, xylem fibre and xylem parenchyma.

food.

2. It is situated towards the outer side.

3. It has no mechanical functions.

4. Phloem is made up of sieve tube, companion cells, phloem parenchyma and phloem fibres.

Primary xylem is of two types- protoxylem and metaxylem. In stem, protoxylem lies in centre and metaxylem towards periphery. This type of primary xylem is called endarch.

In roots, protoxylem lies in periphery and metaxylem lies towards the centre. This type of primary xylem is called exarch.

In gymnosperms, albuminous cells and sieve cells lack sieve tube and companion cells.

Epidermal Tissue System

It forms the outermost covering of whole plant body, which consists of epidermal cells, stomata, epidermal appendages (trichomes and hairs).

Epidermis is single layered, parenchymatous with waxy thick layers of cuticle to prevent water loss.

Stomata is present in epidermis of leaves. It regulates the transpiration and gaseous exchange. In dicots, stomata are bean-shaped having two guard cells

closing the stomatal pore. In monocots, stoma is dumbbellcontain chloroplasts and help in opening and closing of stomata.

Guard cells are surrounded by subsidiary cells. The stomatal aperture, guardcells and the surrounding subsidiary cells are together calledapparatus

Dicots (Bean shaped) Monocots (Dumb

Epidermis also contains a number of hairs. Root hairs are unicellular elongation of epidermal cells. Trichomesbranched or un-branched preventing water loss due to transpiration.

The ground Tissue System

All the tissue between epidermis and vascular bundle forms the ground tissues. It consists of simple permanent tisscortex, pith and medullary rays in stem and roots.

In leaves the mesophyll, chloroplast containing cell, forms the ground tissues.

The Vascular Tissue System

The vascular system consists of complex tissues, xylem antogether form vascular bundles.

When xylem and phloem within a vascular bundle are arranged in alternate manner on different radii, the arrangement are called

closing the stomatal pore. In monocots, stoma is dumbbellcontain chloroplasts and help in opening and closing of stomata.

Guard cells are surrounded by subsidiary cells. The stomatal aperture, guardlls and the surrounding subsidiary cells are together called

Dicots (Bean shaped) Monocots (Dumb-bell shaped)

Epidermis also contains a number of hairs. Root hairs are unicellular elongation of epidermal cells. Trichomes are present on stems, which are multicellular,

branched preventing water loss due to transpiration.

All the tissue between epidermis and vascular bundle forms the ground tissues. It consists of simple permanent tissues. Parenchyma is present in pericycle, cortex, pith and medullary rays in stem and roots.

In leaves the mesophyll, chloroplast containing cell, forms the ground tissues.

The vascular system consists of complex tissues, xylem antogether form vascular bundles.

When xylem and phloem within a vascular bundle are arranged in alternate manner on different radii, the arrangement are called radial

closing the stomatal pore. In monocots, stoma is dumbbell-shaped. Guard cells contain chloroplasts and help in opening and closing of stomata.

Guard cells are surrounded by subsidiary cells. The stomatal aperture, guard lls and the surrounding subsidiary cells are together called stomatal

Epidermis also contains a number of hairs. Root hairs are unicellular elongation are present on stems, which are multicellular,

branched preventing water loss due to transpiration.

All the tissue between epidermis and vascular bundle forms the ground tissues. ues. Parenchyma is present in pericycle,

In leaves the mesophyll, chloroplast containing cell, forms the ground tissues.

The vascular system consists of complex tissues, xylem and phloem that

When xylem and phloem within a vascular bundle are arranged in alternate radial as in roots. When

xylem and phloem are situated at the same radius of called conjoint as in stem and leaves.

Radial Dicotyledonous Root

The outermost layer of dicot root is The cortex consists of several layers of thin The innermost layer of cortex is called

suberin as casparianMonocotyledonous Root

The anatomy of the monocot root is similar to the dicot root in many respects.It has epidermis, cortex, endodermis, pericycle, vascular bundles and pith. Ascompared to the dicot root which have fewer xylem bundles

Dicotyledonous Stem

Epidermis: is covered with a thin layer of cuticle and may have Trichomes and stomata.

Cortex: The cortex is made up of the multiple layers of cells including hypodermis, middle layer of parenchyma cells and innermost layer called endodermis.

Endodermis cells are rich in starch grains and are called the starch sheath. Pericycle is present on the innerparenchyma between the vascular bundles are called medullary rays.

A large number of vascular bundles are arranged in a ring. Each vascular bundle is conjoint, open. Protoxylem is endarch

Monocotyledonous Stem

The hypodermis is made up of sclerenchyma. Vascular bundles are conjoint, closed and scattered. Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.

Phloem parenchyma is absent. Watervascular bundles.

Dorsiventral (Dicotyledonous) Leaf

The leaf lamina of a dorsiventral leaf has 3 parts:vascular system.

The upper epidermis is called adaxial epidermis and lower one is called abaxial epidermis. More number of stomata ar

xylem and phloem are situated at the same radius of vascular bundle, it is as in stem and leaves.

The outermost layer of dicot root is epidermis containing unicellular root hairs.consists of several layers of thin-walled parenchyma cells.

innermost layer of cortex is called endodermis having waxy material casparian strips, which is impermeable to water.

The anatomy of the monocot root is similar to the dicot root in many respects.It has epidermis, cortex, endodermis, pericycle, vascular bundles and pith. Ascompared to the dicot root which have fewer xylem bundles

Epidermis: is covered with a thin layer of cuticle and may have Trichomes and

e cortex is made up of the multiple layers of cells including hypodermis, middle layer of parenchyma cells and innermost layer called

Endodermis cells are rich in starch grains and are called the starch sheath. Pericycle is present on the inner side of endodermis. Layers of radially placed parenchyma between the vascular bundles are called medullary rays.

A large number of vascular bundles are arranged in a ring. Each vascular bundle is conjoint, open. Protoxylem is endarch

The hypodermis is made up of sclerenchyma. Vascular bundles are conjoint, scattered. Each vascular bundle is surrounded by a

sclerenchymatous bundle sheath.

Phloem parenchyma is absent. Water-containing cavities are present within the

Leaf

The leaf lamina of a dorsiventral leaf has 3 parts: epidermis, mesophyll and

The upper epidermis is called adaxial epidermis and lower one is called abaxial epidermis. More number of stomata are present on the abaxial epidermis.

vascular bundle, it is

containing unicellular root hairs. walled parenchyma cells.

having waxy material , which is impermeable to water.

The anatomy of the monocot root is similar to the dicot root in many respects. It has epidermis, cortex, endodermis, pericycle, vascular bundles and pith. As compared to the dicot root which have fewer xylem bundles

Epidermis: is covered with a thin layer of cuticle and may have Trichomes and

e cortex is made up of the multiple layers of cells including hypodermis, middle layer of parenchyma cells and innermost layer called

Endodermis cells are rich in starch grains and are called the starch sheath. side of endodermis. Layers of radially placed

parenchyma between the vascular bundles are called medullary rays.

A large number of vascular bundles are arranged in a ring. Each vascular bundle

The hypodermis is made up of sclerenchyma. Vascular bundles are conjoint, scattered. Each vascular bundle is surrounded by a

containing cavities are present within the

epidermis, mesophyll and

The upper epidermis is called adaxial epidermis and lower one is called abaxial e present on the abaxial epidermis.

There are two types of cells in the mesophyll: palisade parenchyma and spongy parenchyma. The palisade parenchyma is placed adaxially.

The spongy parenchyma is situated below the palisade parenchyma and extends to the lower epidermis. There are numerous large spaces and air cavities between the cells of spongy parenchyma.

Vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.

Isobilateral (Monocotyledonous) Leaf

Stomata are present on both the surfaces of an isobilateral leaf. The mesophyll is not differentiated into palisade and spongy parenchyma.

Some adaxial epidermal cells in grasses are modified into large, empty cells called bulliform cells. When the bulliform cells absorb water, they become turgid. So the leaf surface is exposed. During water stress, when the bulliform cells become flaccid, the leaves curl inwards to minimize water loss.

SECONDARY GROWTH The increase in girth of a plant body is called secondary growth. The tissues involved in secondary growth are: vascular cambium and cork cambium. Vascular Cambium: In case of young stem vascular cambium is present in patches as a single layer between the xylem and phloem. It forms a complete ring at a later stage. Activity of the Cambial Ring:

The cambial ring becomes active and begins to cut off new cells, both towards the inner and the outer sides.

The cells which are cut off towards pith mature into secondary xylem. The cells which are cut off towards periphery mature into secondary phloem.

The cambium is more active on the inner side than on the outer. As a result, the amount of secondary xylem produced is more than secondary phloem. The primary and secondary phloems get gradually crushed due to the continued formation and accumulation of secondary xylem.

At some places, the cambium forms a narrow band of parenchyma, which passes through the secondary xylem and the secondary phloem in the radial directions. These are the secondary medullary rays

Spring wood and autumn wood:

Cambium is very active during the spring season, but less active during the winters. Hence, during spring; a large number of xylem elements are formed having wider vessels. During winter, less xylem elements are formed having narrow vessels.

The wood formed during summer is called spring wood. The wood formed during winter is called autumn wood.

The two kinds of wood appear as alternate concentric rings in transverse section of a trunk of a tree. These are called annual rings and provide information about age of the tree.

Heartwood and sapwood:

In old trees, the greater part of secondary xylem is dark in colour, hard, and resistant to attacks by microorganisms and insect. This region is made of dead elements with highly lignified walls. This wood is called heartwood. The heartwood gives mechanical support but does not conduct water.

The peripheral part of the secondary xylem is lightly coloured. This is known as sapwood. It helps in conduction of water and minerals.

Cork Cambium

Mmeristematic tissue which develops in the cortex region is called cork cambium or phellogen.

The phellogen cuts off cells on both sides. The outer cells differentiate to form cork or phellem while the inner cells differentiate into secondary cortex or phelloderm.

Phellogen, phellem and phelloderm are collectively called periderm.

Due to activity of the cork cambium, pressure builds up on the remaining layers peripheral to phellogen. These layers gradually die and fall off.

Lenticels

At certain regions, the phellogen cuts off closely arranged parenchymatous cells on the outer side instead of cork cells. These parenchymatous cells soon rupture the epidermis, forming a lens-shaped openings called lenticels.

Lenticels permit the exchange of gases between the outer atmosphere and the internal tissue of the stem.

Secondary Growth in Roots

The vascular cambium of the dicot root originates from the tissue located just below the phloem bundles. A portion of pericycle tissue present above the protoxylem forms a continuous wavy ring. It gradually becomes circular. Rest of the steps are similar as in dicot stem.

Secondary growth takes place in stems and roots of gymnosperms. No secondary growth occurs in monocots.

Exercises

NCRT TEXTBOOK QUESTIONS SOLVED

1.State the location and function of different types of meristems. Soln. Meristems are of three types on the basis of their location in plant body: (i) Apical meristem: It is present at the apices of root and shoot and is responsible for increase in length. (ii)Intercalary meristem: It is present at the bases of leaves above the nodes or below the nodes and is responsible for elongation of the organs. (iii)Lateral meristem : It is present on lateral side and is responsible for increase in girth or diameter.

2.Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain. Soln. Yes, I agree with this statement. Cork cambium cuts off cells both on its outer side and inner side. The cells cut off on outer side form cork and cells cut off on inner side form secondary cortex. The cells of cork are dead whereas those of secondary cortex are living.

3.Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance? Soln. Secondary growth is the formation of secondary tissues from lateral meristems. It is found in dicots only. It increases the diameter of the stem. Secondary tissues are formed by two types of lateral meristems, vascular cambium and cork cambium. Vascular cambium produces secondary vascular tissues while cork cambium forms periderm.The vascular bundles in dicot stem are conjoint, collateral, open and are arranged in a ring. The cambium present between xylem and phloem in vascular bundles is called fascicular or intrafascicular cambium. Besides this, some cells of medullary rays also become meristematic and this is called interfascicular cambium. Both these cambia collectively constitute complete ring of vascular cambium. This ring of vascular cambium divides periclinally to cut off cells both on inner side and outer side. The cells cuts off on outer side are secondary phloem and inner side are secondary xylem. Amount of secondary xylem cut off is more than secondary phloem and thus with the formation of secondary tissue, increase in girth or diameter occurs. The structure of secondary xylem and secondary phloem is similar to that of primary xylem and primary phloem. With the increase in secondary tissue, the primary xylem and primary phloem get crushed. The ray initials of vascular cambium ring divide by tangential divisions and add new cells. These new cells produced on both the sides of ray initials remain meristematic for sometime and then differentiate into parenchymatous cells of rays. The rays, produced by vascular cambium in between the secondary xylem and secondary phloem, are called secondary medullary rays. They are usually one to few layers in thickness and one to several layers in height. The medullary rays form the radial systejn responsible for radial conduction of solutes. They maintain connection between pith and cortex There is a marked difference in activity of cambium with change in season. In spring, the activity of cambium is more and hence the wood elements are larger in size with wide lumen. The activity of cambium is less during autumn and the wood elements are smaller in size with narrow lumen. Spring wood and autumn wood of a year constitute annual ring. In order to increase in girth and prevent harm on the rupturing of the outer ground tissues due to the formation of secondary vascular tissues, dicot stems produce a cork cambium or phellogen in the outer cortical cells. Phellogen cells divide on both the outer side as well as the inner side to form secondary tissues. The secondary tissue formed on the inner side is

called secondary cortex while the tissue formed on outer side is called cork.

Significance of secondary growth is as follows: (i) It adds to the girth of the plant thus provides support to increasing weight of aerial parts due to growth. (ii)It’ produces a corky bark around the tree trunk that protects the interior from abrasion, heat, cold and infection. (iii)It adds new vascular tissues for replacing old non-functioning one as well as for meeting increased demand for long distance transport of sap and organic nutrients.

4.Draw illustrations to bring out the anatomical difference between (a) Monocot root and dicot root (b) Monocot stem and dicot stem Soln.(a) Differences between monocot root and dicot root are illustrated in the following figure and table.

(b) Differences between monocot and dicot stems are illustrated in the following figure and table.

5.Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem ? Give reasons. Soln. Vascular bundles in dicot stem are arranged in a ring whereas in monocot stem vascular bundles are scattered throughout the ground tissue. On the basis of arrangement of vascular bundles it can be ascertained whether the young stem is dicot or monocot. Besides undifferentiated ground tissue, sclerenchymatous hypodermis, oval or circular vascular bundles with Y shaped xylem are other differentiating features of monocot stem.

6.The transverse section of a plant material shows the following anatomical features – (a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheath, (b) phloem parenchyma is absent. What will you identify it as? Soln. The plant material is identified as monocot stem.

7.Why are xylem and phloem called complex tissues? Soln. A group of different types of cells which perform common function is called complex tissue. Xylem and phloem are called complex tissues as all cells that work as a unit for a common function have different structural organisation. Xylem has four types of cells-tracheids, vessels, xylem parenchyma and xylem fibres. Phloem consists of sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Xylem is associated with conduction of water and minerals from roots to top of plants and phloem is responsible for transport of organic food.

8.What is stomatal apparatus? Explain the structure of stomata with a labelled diagram. Soln.Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed*of two bean shaped cells known as guard cells which enclose stomatal pore. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.

9.Name the three basic tissue systems in the flowering plants. Give the tissue names under each system. Soln. The three basic tissue systems in flowering plants are epidermal tissue system, ground tissue system and vascular tissue system.

Epidermal tissue system comprises epidermal cells, stomata, trichomes and hairs.

Ground tissue system consists of cortex, endodermis, pericycle, pith and medullary rays, in the primary roots and stems. In¬leaves, the ground tissue consists of thin walled chloroplast containing cells and is called mesophyll. The vascular tissue system consists of complex tissues, the phloem and the xylem.

10.How is the study of plant anatomy useful to us? Soln. Study of internal structures of plants is called plant anatomy. Study of plant anatomy is useful: -for solving taxonomic problems.

-for knowing homology and analogy of various plant groups. -to differentiate the superior and inferior, standard and substandard or specified and unspecified woods. -in establishing purity and correct identity of plant parts in pharmacognosy (science connected with sources, characteristics and possible medicinal uses). -in knowing the structural peculiarities of different groups of plants.

11 .What is periderm? How does periderm formation take place in the dicot stems? Soln. phelloderm, phellogen and phellem together constitute the periderm. Periderm is protective in function.Dicot stems produce cork cambium or phellogen in the outer cortical cells. Phellogen cells divide on both the outer side as well as the inner side to form secondary tissues. The secondary tissue produced on the inner side of the phellogen is called secondary cortex or phelloderm. On the outer side phellogen produces cork or phellem.

12. Describe the internal structure of a dorsiventral leaf with the help of labelled diagram. Soln.

Dorsiventral leaves are found in dicots. The important anatomical features of dorsiventral leaves are discussed below: (a) Upper epidermis : This is generally outermost single layer made of parenchymatous cells. The epidermal cells have sometimes outgrowths called papillae, e.g., in Gladiolus. The epidermal cells are devoid of chloroplast and stomata are absent on upper epidermis. (b) Lower epidermis : It is just like upper epidermis but here stomata are present. Chloroplasts are absent in lower epidermis also, except the guard cells of stomata. (c)Mesophyll: In between upper and lower epidermis mesophyll tissue is present which can be divided into two regions: (i)Palisade parenchyma : These are elongated columnar cells without intercellular spaces. These have chloroplast in them and are generally arranged in two layers.

(ii)Spongy parenchyma : It is found below palisade parenchyma and are spherical or oval with intercellular spaces. They also have chloroplasts but number of chloroplasts is more in palisade parenchyma than spongy parenchyma. (d)Vascular bundles : Vascular bundles are. generally found at the boundary between the palisade and the spongy regions. The vascular bundle in midrib region is largest. Vascular bundles are conjoint, collateral and closed. Each vascular bundle is surrounded by a bundle sheath of parenchymatous cells. In the vascular bundle, xylem is present towards upper epidermis and phloem towards lower epidermis. Further in xylem, protoxylem is towards upper epidermis.