Chapter 1: Earth's Ecosystems

Chapter 1 Chapter 2

About 8,000 waves

strike the Big Sur

coastline every day.

Earth’s Ecosystems

CHAPTER 1

How do organisms exchange energy

and nutrients in an ecosystem?

20

Lesson 1Introduction to Earth’s Ecosystems

PAGE 24

Lesson 4Earth’s Food Chains, Webs, and Pyramids

PAGE 66

Lesson 2Photosynthesis: The Basic Process of Life

PAGE 40Lesson 3Microscopic Organisms on Earth

PAGE 54

Lesson 5Earth’s Cycles for Life

PAGE 806 LS 5. Organisms in ecosystems exchange energy and nutrients among themselves and with the environment.

21

ELA R 6.3.6. Identify and

analyze features of themes conveyed through characters, actions, and images. • ELA W 6.2.4. Write responses to literature.

LiteraturePOEM

22

Redwood trees rise like skyscrapersFingering the clouds in search of moisturePulling down the fog and passing itFrom limb to limbInto the deep of the forest.The fog blankets the forestBlocking out light, movement, and soundLike a curtainDraped across a stage.Yet behind the redwood curtainBlack bear walk and stalk their preyDeer sleep and leap awaySlugs climb and slime on leavesBirds sing and wing in the breeze.The show must go onAs it has for thousands of yearsBehind the redwood curtain.

Write About ItResponse to Literature In this poem the author describes a forest. What is life like in this forest? What plants and animals live there? Write an essay explaining the main idea of the poem. Use details from the poem to show how the author makes her point.

-Journal Write about it online @ www.macmillanmh.com

by Natasha Wing

from MY AMERICAed. Lee Bennet Hopkins

23

http://www.macmillanmh.com

Introduction to Earth’s Ecosystems

Lesson 1

California is home to one of the most diverse collections of living things in the world. Why do you think this is so?

6 LS 5.e. Students know the number and types of organisms an ecosystem can support depends on the resources available and on abiotic factors, such as quantities of light and water, a range of temperatures, and soil composition.24

ENGAGE

Materials

• trowel or spade

• 4 small stakes

• meterstick

• string

• thermometer

• fi eld guides

• graph paper

• safety goggles

Do different ecosystems contain

different organisms?

Form a HypothesisWhy do certain plants and animals live in certain places? How does the amount of sunlight affect different organisms? Write your answer as a hypothesis in the form “If a plant needs lots of sunlight, then . . .”

Test Your Hypothesis

Experiment With your teacher select two areas on or near your school grounds to study. Choose one area that receives plenty of sunlight and another that receives very little. Mark off a 2-by-2-meter plot in each area with stakes and string.

Measure Measure the air temperature at ground level and at 1 meter above ground level in each area.

Record Data Using graph paper record the locations of the living things in each area. What kinds of organisms do you see? Use field guides to help you identify the organisms.

Draw Conclusions

Compare your observations about the two areas. How do the temperatures differ? Which area contains more living things? What statement can you make about the effect of sunlight on an ecosystem?

How do you think the amount of water in an ecosystem affects living things? Make a prediction about this, and design a procedure to test it. How have people affected the ecosystem?

Explore MoreStep

Step

6 IE 7.a. Develop a hypothesis. • 6 IE 7.e. Recognize whether evidence is consistent with a proposed explanation.

25EXPLORE

What Is an Ecosystem?A system is a group of things that work

together as a unified whole. There are systems all around you. Our bodies contain organ systems for breathing and for digesting food. Schools are organized into school systems. Planets are part of our solar system. Each system is made up of parts that interact with one another closely.

The living things in an area also work together in systems. They all depend on the same resources and are affected by changes that occur around them. For example, a major change in a nonliving part of an ecosystem, such as an extreme drought, can affect all the organisms in an ecosystem.

Living things are part of an ecosystem. An ecosystem consists of the living and nonliving things in an area that interact with one another.

An Ecosystem

▶ Main Idea 6 LS 5.e

The number and types of organisms in an ecosystem depend on the resources available.

▶ Vocabularyecosystem, p. 26

biotic factor, p. 27

abiotic factor, p. 27

humus, p. 32

topsoil, p. 32

minerals, p. 32

acidity, p. 33

alkalinity, p. 33

ecology, p. 34

population, p. 34

community, p. 35

habitat, p. 36

niche, p. 36

-Glossary @ www.macmillanmh.com

▶ Reading SkillMain Idea

Explore ecosystems with a park ranger.

26EXPLAIN


Ecosystems

Any living thing that is part of an ecosystem is a biotic factor . This term includes the root bio, which means “living.” Living things include tiny organisms, such as bacteria, as well as the plants and animals people can see. Any nonliving part of the ecosystem, such as water, minerals, sunlight, air, or soil, is an abiotic factor . This term includes the prefix a-, which means “not” or “without.”

How can you identify the abiotic factors in an ecosystem? Abiotic factors are the parts of the ecosystem that help make life possible. For example, sunlight provides warmth and energy. Rocks provide shelter and, in time, form soil. Water is so important to living things that it is what scientists

look for first when searching for signs of life on other planets. Other abiotic factors include air, climate, and altitude. All these factors influence the number and types of organisms that can live in an ecosystem.

Identifying the living things in an ecosystem might seem to be easy. At the beach you might see birds, fish, seals, and seaweed. In contrast, think about microscopic organisms inside your mouth. The warm, moist environment there supports millions of bacteria.

How would the abiotic factors shown here affect the organisms that live in the pond?

Clue: What are the nonliving things in the picture?

Reading Diagrams

Quick Check

Main Idea What are five abiotic

factors in an ecosystem?

Critical Thinking How do biotic

and abiotic factors differ?

27EXPLAIN

Why are sunlight and

temperature important?The amount of sunlight a

location receives directly affects the temperature in that location. Temperature, in turn, affects the number and types of animals and plants that can survive in a location.

Sunlight

Areas of Earth that receive greater amounts of sunlight have higher temperatures than other areas. The equator is the part of Earth that receives the most direct sunlight. Areas around the equator that are not at extremely high elevations are generally known for their lush vegetation and great diversity of living things.

The parts of Earth that receive the least direct sunlight are the North and South poles. Areas near the poles have sparse or no vegetation and fewer kinds of living things. For most organisms, especially plants, sunlight is an important abiotic factor.

Temperature

Temperature change is another factor that affects living things. In some regions the temperature changes very little.

◀ Parrots thrive in warm climates, such as the Amazon rain forest.

28EXPLAIN

▼ These penguins are adapted to the temperatures in their Antarctic surroundings.

In tropical rain forests, for example, the temperature stays around 80°F (27°C) almost all the time. Many animals and plants thrive in places where the temperature does not change much in a single day.

In other places, the temperature may vary from day to night and from season to season. In deserts the temperature can vary from about 32°F (0°C) to more than 100°F (38°C) in a single day. The plants and animals in a desert must be able to survive these wide variations in temperature.

Changes in the seasons have similar effects. Most organisms survive better in warm, mild summers than in cold, icy winters. In places where the temperature changes a great deal with

Quick Check

Main Idea How does temperature

affect organisms in rain forests?

Critical Thinking How does the

amount of direct sunlight affect

the plant growth in an area?

the seasons, some organisms migrate, or travel to a different place. Others become dormant, or less active, or have other adaptations that enable them to survive.

29EXPLAIN

Central Valley irrigation

Why is water important?Without a steady supply of water, life would not exist on Earth.

Water helps living things in several ways. It keeps cells strong and healthy. Cells are the basic units of life. Water dissolves and transports substances. It also helps regulate the temperature of an organism.

Your Body’s Need for Water

Press your hands together, and they will seem firm and solid. However, about 60% to 70% of your body is made up of water. Some parts of your body have an even greater percentage of water. It is no wonder that water is so important to your survival.

Water is the body’s main transportation vehicle. Many substances dissolve in water. This property of water is what makes it so vital to life. Water carries nutrients, oxygen, and other substances to various parts of your body. Water also carries waste materials out of your body.

Water helps regulate your body’s temperature. It cools your skin, making you feel cooler all over. It also helps carry excess heat away from your cells.

30EXPLAIN

Plants’ Need for Water

Plants, too, are made up mostly of water. Some parts of a plant, such as the leaves and stems, may be as much as 90% water. Water transports minerals and nutrients throughout the plant.

Water keeps plant cells rigid. You have probably seen what happens when a plant does not receive enough water. The leaves and stems become weak, and the plant wilts.

Plants need water to grow. For this reason, the amount of water in an area affects the number and types of plants that live there. Areas with little rainfall, such as deserts, have fewer plants. The plants that do grow there have special adaptations that allow them to conserve water.

Plants that grow in areas that receive little rain have adapted to the dry conditions. For example, the shape of the barrel cactus enables it to expand when rain falls and to shrink during dry times. When it expands, this cactus stores water in its spongy tissues. Animals have adaptations for drought and heat, too. The kit fox has large ears with dense networks of veins. These veins help the fox’s body shed heat.

One way that humans adapt to dry conditions is to use irrigation. In places where not enough rain falls to grow crops, farmers water their fields. Water taken from the Colorado River, for example, irrigates almost 1 million acres of land in Southern California. This water helps crops such as lemons, grapes, oranges, lettuce, and tomatoes grow on land that would otherwise be too dry for farming.

Quick Check

Main Idea Why do plants need

water?

Critical Thinking Why is water

good for transporting substances

in plants and animals?

▲ barrel cactus, Anza-Borrego Desert State Park, California

31EXPLAIN

Why is soil important?Soil supplies the water, air, and

nutrients that plants need in order to grow. By supporting the growth of plants, soil helps living things survive. Conservation of soil is important. We can put plants on hillsides so the soil will not erode. Farmers conserve soil by rotating their crops and letting fields lie fallow, or unplanted, every few seasons.

Soil Layers

Topsoil is the upper layer of soil, which is made mostly of humus, minerals, water, and air. The humus in topsoil is spongy and holds water very well. This makes topsoil an ideal material for plants to live in.

Soil is made up of weathered rock and humus (HYEW•muhs). As rock weathers it breaks down slowly into tiny pieces. Humus is the material in soil formed by the breakdown of plant and animal remains. It mixes with the bits of rock and adds nutrients to the soil.

The substances in soil affect the types of organisms that can live in it. Some compounds known as acids can harm living things if they are present in high

Minerals are the naturally occurring solid materials of Earth’s crust. They include clay, sand, and silt.

The layer below the topsoil is called the subsoil. Some humus can be found near the top of this layer. As water seeps through the topsoil into the subsoil, it brings particles of minerals and clay with it.

Below the subsoil is partly weathered parent rock. The parent rock is the rock from which the soil is formed. There is no humus at this depth.

Below this layer is solid rock, or bedrock.

32EXPLAIN

antacid(pH 10)

concentrations. Acidity is the amount of acid in a substance. Other compounds, known as alkalis (AL•kuh•lighz), or bases, may also be present in soil. Alkalinity (al•kuh•LIN•uh•tee) is the amount of base in a substance.

The acidity or alkalinity of soil is measured on a scale known as the pH scale. The lower the pH, the more acidic the soil is. The higher the pH, the more basic or alkaline the soil is. The pH of the soil in an area helps determine which plants will grow there. If the pH of the soil changes greatly, the plants there may not be able to survive.

Testing Soil pH

Put three different soil samples in separate cups.

Using the soil-test kits provided by your teacher, test the pH of each sample. Record the pH of each.

Predict What do you think would happen if you added an antacid to the soil samples? Design an experiment to test your prediction.

Quick Check

Main Idea Why is soil important?

Critical Thinking Why should

people test soil before growing

crops in it?

The pH Scale

lemon(pH 2)

tomato(pH 4)

milk(pH 6)

distilled water(pH 7)

householdammonia(pH 11)

drain cleaner(pH 13)

33EXPLAIN

California sea lions

What lives in an ecosystem?All the abiotic factors in an area,

including temperature ranges, sunlight, water, and soil type, influence what living things are found there. Every organism in the ecosystem plays an important role. The study of organisms and how they interact in an ecosystem is ecology (ee•KAHL•uh•jee). Scientists who study this subject include ecologists, zoologists, biologists, foresters, geologists, and geographers.

In an ecosystem, all the organisms of one species make up a population . The millions of bacteria living in your mouth make up a population. The thousands of elephant seals living in the waters off California are another

population. At one time, people hunted elephant seals for their oil until only about 100 remained. Today, there are many elephant seals along California’s coast. California sea lions are social animals. The females recognize their pups by their sounds and their smells.

Ecologists study populations, looking at the role each population plays in the ecosystem. They might observe behaviors such as breeding and feeding. Members of a population, or species, breed with one another and produce offspring. They also compete for resources such as food, water, and shelter. Almost all populations are influenced by the human population.

34EXPLAIN34EXPLAIN

Populations interact with other plants and animals in their ecosystem. Different species can compete with each other and may even try to eat each other. They can also help each other.

Populations and Communities

All the populations living in an area make up a community . To understand this think about an orchestra. All the violins in the orchestra would make up one population, the cellos another, the clarinets another, and the trumpets another. Each group of instruments represents a population, and each group makes a unique contribution to the community, or the orchestra.

Communities are often named after the locations in which they are found. Cactuses, sagebrush, kangaroo rats, and jackrabbits are part of a desert community. Frogs, minnows, cattails, and dragonflies live in a pond community. Each community includes a group of populations that can survive in the conditions found there.

Tide-pool communities are found where the ocean meets the land. Organisms must be able to withstand the changing tides and the motion of the waves.

Quick Check

Main Idea What is ecology?

Critical Thinking What is the

difference between a community

and an ecosystem?

Tide-Pool Community

What items in the photo show that this is a tide-pool community?

Clue: What kinds of organisms and land features do you see?

Reading Photos

35EXPLAIN

What roles do

organisms have?The success of an ecosystem

depends on its ability to sustain life. For life to thrive, there must be plenty of resources, such as food and water. In addition, the interactions among living things must be in balance. To achieve this balance, each member of a community has a role to play.

A habitat is the place in which a population lives. Your home is a habitat. It provides you with the shelter and food you need to survive. All of an organism’s needs must be met by its habitat. If you have ever set up an aquarium, you know that fish require water, the proper temperature, food, and oxygen. Some types of fish and other aquatic organisms can share a habitat. In natural ecosystems several populations may share the same habitat.

The role of an organism in an ecosystem is called a niche (nitch). A niche includes everything the

organism does and everything it needs. Although organisms may share habitats, they may not occupy the same niche. Suppose everyone in your town had the same job and tried to eat at the same time in the same place. The competition would become fierce. Towns, and ecosystems, are successful because individuals and groups make different contributions.

Some populations occupy niches of such importance that many other organisms depend on them. These populations are called keystone species. For example, beavers build dams that flood the surrounding area, creating valuable wetlands. These wetlands are a rich habitat for a wide variety of living things.

Wetlands help control flooding, filter pollutants from water supplies, and serve as habitats for many organisms.

Quick Check

Main Idea What is a habitat?

Critical Thinking Why can

populations share a habitat

but not a niche?

36EXPLAIN

Math LinkWriting Link

Summarize the Main Idea

Ecosystems are areas where living things interact with each other and with nonliving things. (pp. 26–27)

Sunlight and temperature are among abiotic factors that influence the living conditions in an area. (pp. 28–33)

Populations include all the organisms of one species. Communities include all populations living in an area. (pp. 34–35)

Make a Study GuideMake a layered-look book (see pp. 487–490). Use the titles shown. On the inside of each fold, write two sentences about the main idea of the topic.

Think, Talk, and Write Main Idea What determines the number and types of organisms in an ecosystem?

Vocabulary In an ecosystem, all organisms of one species make up a(n) .

Main Idea What is the difference between biotic and abiotic factors?

Critical Thinking If deserts had more plant life, do you think that a greater variety of animals would live there? Why or why not?

Test Practice Which of these is considered one of the layers of soil?A alkalinityB acidityC bedrockD humus

Test Practice Which of the following is an abiotic factor?A plantsB sunlightC animalsD people

Expository WritingResearch an endangered species (plant

or animal) in or near the ecosystem in

which you live. What biotic and abiotic

factors have contributed to the decline

of this species?

Monitor Population GrowthA state park contains 200 deer. If the

deer population doubles every year for

3 years, how many deer will live in the

park? Make a line graph to show how

the population changes over time.

-Review Summaries and quizzes online @ www.macmillanmh.com 37EVALUATE


A landslide damaged these

homes in Laguna Beach.

These homes in Laguna Beach were unaffected by a landslide.

CompareWhen scientists compare they look for

similarities among objects, materials, and data. As scientists study a particular ecosystem over time, they can make comparisons. They can compare the way the ecosystem functions in the present with the way that it functioned in the past. With this information they can predict what the ecosystem might be like in the future.

Learn It

When scientists study an ecosystem, they examine every change they can. Scientists study changes because one small change in an ecosystem can affect many biotic and abiotic factors.

Charts and Venn diagrams are tools used to compare. After you have collected and recorded data, you can see at a glance whether the data, objects, or materials are similar or not. Line graphs and bar graphs can also be used to analyze changing conditions over time.

Try It

▶ Scientists monitor how sudden events such as floods and mudslides affect an ecosystem. In this activity you will compare a miniature landscape before and after a “flood.” You will need a dishpan, soil, rocks, small twigs, water, and a watering can.

▶ Build a hill landscape of soil, rocks, and twig “trees” in a dishpan. Draw a picture of your landscape on a chart like the one on this page. Use the watering can to sprinkle water gently on your hills. Record your observations.

▶ Hold the can high, and continue to let water fall down on the hills. Record your observations. Pour the rest of the water quickly over the hills. Record your observations. Draw a picture of the way your landscape looks now.

38EXTEND

Apply It

▶ Now use the information from your chart to create a Venn diagram like the one on this page. Draw two overlapping ovals. In one oval list the characteristics of your hill ecosystem before the “flood.” In the other oval, list the characteristics of your hill ecosystem after the “flood.” Write the common characteristics in the area where the two ovals overlap.

▶ How did your hill ecosystem change?

▶ How did it stay the same?

▶ Next, choose an ecosystem near your school or home to observe for a month. Note any changes in the ecosystem, and make a chart or Venn diagram to compare its characteristics at the beginning and at the end of the month.

6 IE 7.h. Identify changes in natural phenomena over time without manipulating the phenomena (e.g., a tree limb, a grove of trees, a stream, a hillslope).

39EXTEND

Photosynthesis: The Basic Process of Life

Lesson 2

Energy from the Sun helps a plant grow. A hummingbird gets food and energy from a plant. How does sunlight produce energy?

6 LS 5.a. Students know energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis and then from organism to organism through food webs.40

ENGAGE

Materials

• growing plant (a large-leafed plant will work best)

• aluminum foil

• paper clips

• water

How does light affect plants?

Form a HypothesisPlants need light to grow. What do you think will happen to a plant’s leaves if you cover parts of them, so that no light reaches those parts? Write your answer as a hypothesis in the form “If parts of a plant’s leaves do not receive any light, then . . .”


Wrap small pieces of aluminum foil over parts of several leaves. Wash your hands after handling the plant.

Use Variables Cover at least four different leaves of the plant in the same way.

Place the plant in a window where it will get lots of light. Water the plant with a measured amount of water.

Experiment After one day, carefully lift the foil and check each leaf. Write down your observations. Gently replace the foil in the same position. Continue your observations each day for one week. Replace the foil in the same position each time. How did the areas covered by the foil differ from the other parts of the leaves?

Draw Conclusions

Interpret Data How did the changes you observed progress after one day? After two days? After a week? How do light and darkness affect the growth of leaves?

Remove the foil from the leaves. Water the plant with the same amount of water you used in the previous week, and observe it each day for another week. What happens when the leaves remain uncovered?

Explore More

Step

Step

6 IE 7.a. Develop a hypothesis. • 6 IE 7.d. Communicate the steps and results from an investigation in written reports and oral presentations.

41EXPLORE

▶ Main Idea 6 LS 5.a

Energy enters ecosystems as sunlight, which is used by plants to make food.

▶ Vocabularychloroplast, p. 43

chlorophyll, p. 43

photosynthesis, p. 43

roots, p. 44

stem, p. 45

transpiration, p. 48

respiration, p. 50


▶ Reading SkillSummarize

Why is photosynthesis

important?Every living thing needs energy to live and

grow. Some organisms, such as animals, get their energy from eating plants. Where do the plants get their energy from? Did you know that plants store energy from the Sun in their cells?

Photosynthesis

LightWater + Carbon dioxide → Sugar + Oxygen

Poppies use sunlight to make food.

42EXPLAIN


Photosynthesis

Almost all organisms on Earth depend on the Sun for energy. The Sun’s energy is stored by plants as food during the food-making process. This activity goes on in plant cells that have chloroplasts (KLOR•uh•plasts), structures found in the cells of leaves and stems of green plants. Chloroplasts contain a substance called chlorophyll (KLOR•uh•fil), a green substance in plants that absorbs energy from sunlight. When sunlight falls on a leaf, the chlorophyll traps energy from the Sun.

Photosynthesis (foh•toh•SIN•thuh•sis) is the process of making food by using sunlight. Plants, and some other organisms, take in carbon dioxide from the air and water from the environment. The plant or other organism then changes these two raw materials into two products. The products are sugar, or food, and oxygen.

Inside the chloroplasts the energy from the Sun is used to split the water molecules into hydrogen and oxygen. The hydrogen and oxygen combine with carbon atoms to produce food in the form of sugars. Oxygen, which is given off by the plant as a waste product, enters the atmosphere.

Photosynthesis helps sustain life on Earth. In addition to producing oxygen, which animals breathe, plants also take in carbon dioxide to make food. This helps our environment, because plants act as natural air scrubbers. They absorb carbon dioxide that would otherwise pollute the air. Then they turn it into oxygen that other living things need.

Quick Check

Summarize Where do plants

store energy from the Sun?

Critical Thinking What is

photosynthesis?

coleus plant ▶ chloroplast seen through a microscope

43EXPLAIN

What do roots and stems do?When you think of photosynthesis, which part of the

plant do you think of first? Most people think of the leaves. However, other plant structures play important roles in photosynthesis as well.

Roots

Most roots hold plants in the soil and take in water and minerals to feed the plants. There are two kinds of roots: taproots and fibrous roots. Taproots are thick and straight with a few root hairs along the sides. If you have ever tried to pull a dandelion out of the ground, you know that taproots grow very deep and strong.

Fibrous roots do not grow as deep, but they branch out into a network of thin, hairy roots. These roots can form thick mats. Plants such as marigolds and grass have fibrous root systems.

Some plants, such as orchids, have aerial roots. Aerial roots do not anchor the plant to the ground or absorb minerals from the soil. Instead they reach out above the ground for water and sunlight to nourish the plant. To get the sunlight and water they need, plants with these roots grow high in the branches of rain-forest trees. Their green aerial roots are actually able to carry out photosynthesis.

Roots also store some of the food that the plant produces. This is why edible roots such as carrots, sweet potatoes, and sugar beets have such high nutritional value. When animals eat these roots, energy from the Sun passes along to them.

Parts of a Root

Root Cap A thin covering, made up of cells, that protects the root tip as it grows into the soil

Root Hairs Secondary roots that are threadlike tissues on the surface of the root through which water and minerals enter

Xylem Tissue through which water and minerals flow up through the plant

Phloem Tissue through which food from the leaves moves down through the plant

Epidermis The outermost layer of the root

44EXPLAIN

Soft Stem Woody Stem

cambium

xylem

phloem

Stems

Stems are the parts of a plant that support leaves and flowers. The stem also transports water and other substances between the roots and leaves. Why do you think plants need to hold their leaves up to the Sun? They need to do this so they can receive as much sunlight as possible to carry out photosynthesis.

Look at the diagram on this page. Inside the stem are tubes called xylem (ZIGH•luhm) and phloem (FLOH•uhm). Xylem carries water and minerals up from the roots through the plant to the leaves. Phloem carries food from the leaves to other parts of the plant. Xylem and phloem may be separated by another layer of cells called the cambium.

Stems also help store energy. Like roots some stems store energy in the form of food. Sugarcane is an example

of an edible stem. Some plants, such as asparagus, have photosynthetic cells in their stems that can help make food. Other plants use stems as a reservoir for water. In what environment do you think it is very important for plants to store large amounts of water? You are correct if you said, “The desert.” Some kinds of cactuses can store enough water to get through several days or even several years without rainfall!

Parts of a Stem

How are the xylem, the phloem, and the cambium arranged differently in a woody stem and in a soft stem?

Clue: Compare the drawings of the two types of stems. How are they alike? How are they different?

Reading Diagrams

Quick Check

Summarize What functions do

roots and stems share?

Critical Thinking How do roots,

which are not green, contribute

to photosynthesis?

45EXPLAIN

What are leaves?Look at a leaf from a tree or

a shrub. You might have difficulty accepting the fact that the leaf is such a powerful food-making machine. Inside the thin blade of the leaf are the structures that provide Earth with food, oxygen, and clean air. Leaves with only one blade are simple leaves. Leaves with two or more blades are compound leaves.

The parts of a leaf work together to help keep the plant alive. The outermost part of a leaf is its epidermis (ep•i•DUR•mis). Cells of the epidermis secrete a waxy coating called a cuticle

(KYEW•ti•kuhl). This waxy covering helps prevent water from leaving the plant. The leaf makes food in cells between the layers of the epidermis. These cells contain chloroplasts. The epidermis on the lower surface of a leaf contains many tiny pores called stomata (STOH•muh•tuh) (singular, stoma). Stomata open and close to let gases, such as carbon dioxide and oxygen, in and out. These openings also control the amount of water that leaves the plant. Guard cells surrounding the stomata regulate when the stomata open and close.

Parts of a Leaf

46EXPLAIN

How Leaves Work

The veins that run through the leaf blade bring water and minerals to the last stop on their journey from the roots. When carbon dioxide enters through the stomata and sunlight is captured by the chlorophyll in the chloroplast, all the ingredients are in place to produce food.

Some leaves, such as those of spinach or lettuce, store food. Others are designed to protect the plant. The spines on a cactus are actually the leaves. They do a good job of protecting the plant from being eaten, and their small size and pointed shape minimize water loss in the dry environment of a desert.

In some areas of the world where there are seasonal changes in temperature, plants shut down their food-making factories at certain times of year. During the winter months, they live off the food they have stored. Green chlorophyll disappears from the leaves. When this happens people can see the other colors, such as yellow and orange, that are usually masked by the green pigment. Maple trees, as well as some other plants, store sugar in their leaves. The stored sugars trigger the formation of a red pigment, giving these plants their vibrant autumn colors.

Leaves

Collect a variety of leaves.

Observe Examine each leaf with a hand lens, and write down each structure that you can identify.

Place a piece of white paper over the leaf, and rub back and forth with a crayon, making a print of the leaf.

Identify On the rubbing, identify the leaf as simple or compound, and label each structure.

Using two different-color crayons, trace the flow of water and food through the veins.

Quick Check

Summarize What do leaves do

for a plant?


difference between a simple leaf

and a compound leaf?

47EXPLAIN

sequoia tree, Sequoia National Park, California

How does water move through plants?Roots absorb water and minerals from the soil. The stems

and leaves transport the water and minerals throughout the plant. This might not seem like a huge task in a small plant, but how can water reach the top of a 90-meter (295-foot) giant sequoia?

Several forces work together to move water through a plant. Pressure builds up in the roots and forces water to move upward into the stems. In small plants root pressure alone can move water all the way through the plant. However, in most plants root pressure is not enough to push water through tall stems and into leaves. Forces that pull the water upward are needed as well.

Capillary action is one force that pulls water up into plants. Water molecules stick to one another and to other substances, such as glass, cloth, cells, and soil. You can observe capillary action by dipping the corner of a paper towel into a glass of water. The water will appear to climb up the paper towel.

The other force that pulls water upward through a plant is caused by evaporation. Transpiration (trans•puh•RAY•shuhn) is the loss of water from plant leaves. The water in the plant travels up through the veins of the leaves, and then it evaporates into the atmosphere through the stomata. As the plant loses water, more water moves into the plant cells to take the place of the water that has been lost.

These three forces—root pressure, capillary action, and transpiration—work together to keep water moving through the parts of the plant. These forces help the plant carry out photosynthesis and keep it from wilting.

Quick Check

Summarize What three forces move water upward

through a plant?

Critical Thinking What would happen to the plant if

it did not have stomata on the bottoms of its leaves?

◀ A huge tree can move more than 1,800 liters (476 gallons) of water from the ground to its leaves each day. Most people drink about 2 liters (4 pints) of water each day.

48EXPLAIN

vein

petiole

xylem

How Water Moves Through a Plant

Water and dissolved minerals enter the plant’s root hairs from the soil. Pressure builds up in the roots as water moves in.

What causes water to travel from a plant’s roots to its stem?

Clue: Follow the path of the blue arrows in the diagram, and read the text on page 48.

Reading Diagrams

Watch how plants transport water @ www.macmillanmh.com

The water is pushed upward into the xylem and travels up the stem. Capillary action pulls water up through the xylem.

Loss of water through transpiration in the leaves helps pull the water upward through the xylem toward the top of the plant.

Almost 99% of the water that enters the roots is given off into the air by transpiration through the leaves’ stomata.

Water moves up the stem, through a leaf’s petiole, and into the leaf’s veins. The veins carry the water to the leaf’s cells.

49EXPLAIN


What happens during

respiration?When food is eaten, energy passes from

organism to organism. Every time energy is passed along, some energy is lost. Each organism uses some of the energy for its own daily activities. How does a plant or animal use the energy that is stored in the food it eats?

When an organism needs fuel, its cells can use oxygen to break apart food molecules. The release of energy in plants and animals from food is called respiration (res•puh•RAY•shuhn). In respiration, which occurs in plants and animals, sugars and oxygen join to produce water, carbon dioxide, and energy.

Photosynthesis

LightWater + Carbon dioxide → Sugar + Oxygen

happens only in cells with chloroplasts

needs sunlight

stores energy

turns energy to a sugar

produces oxygen

uses water to make food

uses carbon dioxide

Respiration

Sugar + Oxygen → Carbon dioxide + Water + Energy

happens in most cells

happens in light or dark

releases energy

turns a sugar to energy

uses oxygen

produces water

produces carbon dioxideQuick Check

Summarize What role does

respiration play in cells?

Critical Thinking Why can

photosynthesis and respiration

be considered reverse processes?

Apples contain energy stored during photosynthesis.

50EXPLAIN

Write a NarrativeDescribe the journey of a water

molecule through a plant. How does

it enter the plant? How does it move

through the plant? How does it exit

the plant?

Calculate Oxygen ReleasedA forest produces 56 liters of oxygen

in 1 week. A single plant can produce

1 liter per week. How long will it take

the forest to produce enough oxygen

to fill a 10,000-liter tank?

Writing Link Math Link


Photosynthesis is the process in which plants convert energy from the Sun into usable chemical energy stored as food.(pp. 42–43)

Roots and stems transport water and other substances between the roots and the leaves. (pp. 44–49)

During respiration, plants and animals release energy from food. (p. 50)

Make a Study GuideMake a three-tab book (see pp. 487–490). Use the titles shown. On the inside of each tab, summarize how that topic can help you understand how plants make food.

Think, Talk, and Write Main Idea How does energy enter ecosystems?

Vocabulary The process by which plant leaves lose water is .

Summarize How does root pressure differ from transpiration?

Critical Thinking Explain the relationship between plants and an atmosphere suitable for sustaining life.

Test Practice In addition to carbon dioxide, is one of the products of respiration.A sugarB oxygenC chlorophyllD energy

Test Practice What is the process of making food by using sunlight?A photosynthesisB xylemC transpirationD chloroplast



Until recently scientists thought that all life on Earth depended on sunlight. In the 1970s they made a startling discovery. They found creatures on the ocean floor that did not need sunlight to live. The question, then, was how these creatures could survive on the cold, dark ocean floor.

Earth’s mantle contains hot, melted rock called magma. When breaks in Earth’s crust occur on the ocean floor, magma wells up, fills in the spaces, and gushes forth as a hot liquid called lava.

Good expository writing

▶ introduces the main idea and develops it with facts and supporting details.

▶ gives important information about a topic.

▶ summarizes information from a variety of sources.

▶ uses transition words, such as therefore and then, to connect ideas.

▶ draws a conclusion based on the facts and information presented.

Life in the

These worms live near hot-water vents on the ocean floor. They eat bacteria that live on chemicals in the water.

galatheid crab

ELA W 6.1.2. Create multiple-paragraph expository compositions: a. Engage the interest of the reader and state a clear purpose. b. Develop the topic with supporting details and precise verbs, nouns, and adjectives to paint a visual image in the mind of the reader. c. Conclude with a detailed summary linked to the purpose of the composition.52

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The lava contains large amounts of various chemicals that bacteria feed on. These hot spots are called hydrothermal vents. Scientists found worms, clams, crabs, mussels, and fish living near these vents. The animals survive in this dark environment by eating these bacteria.

Most life on Earth depends on sunlight and on photosynthesis—but not all life does! Nature is full of surprises.

Write About ItExpository Writing Write a report telling how sunlight helps support your life. Engage your reader right away, and clearly state your purpose for writing. Introduce the main idea, and develop it with facts. Use supporting details and precise verbs, nouns, and adjectives to describe and explain your subject. Do print and online research. Summarize your findings at the end of the report.


53EXTEND


Lesson 3

Microscopic Organisms on Earth

Did you ever think about where some of the most amazing and beautiful organisms can be found? Look at several drops of pond water through a microscope. The paramecium shown here is one part of the fascinating world of microscopic organisms.

6 LS 5.b. Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment.54

ENGAGE

What can you see through

a microscope?

Make a PredictionWhat do you think you will see if you look at an onion skin, sand, or yeast under a microscope? Write your prediction in the form “If I look at an onion skin, sand, or yeast under a microscope, then . . .”

Test Your Prediction

Observe Place a piece of newspaper on a microscope slide. Place the slide on the stage of the microscope, and observe it under low power. Draw what you see. Look at the newspaper again under high power. Record your observations.

Observe Select your own samples. Repeat step 1 for each sample. Record what you see.

Record Data Make a data table to record the details of what you observed. How many organisms did you observe? How big were they? What colors were they?

Draw Conclusions

Observe What did you learn about the way objects appear when viewed through a microscope? What happened to your observations as you changed from low power to high power?

Observe Describe the appearance of each of the samples you observed.

Step

Materials

Did you see any differences among the samples under the microscope? Research the types of cells you looked at. Analyze and present your results.

Explore More

Step

• microscope

• 4 microscope slides

• dropper

• water

• toothpick

• small pieces of newspaper

• onion skin

• sand

• yeast

6 IE 7.b. Select and use appropriate tools and technology (including calculators, computers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.

55EXPLORE

Compound Microscope

▶ Main Idea 6 LS 5.b

Energy and matter are transferred from one organism to another at the microscopic level.

▶ Vocabularymicroscope, p. 57

electron microscope, p. 57

prokaryote, p. 58

eukaryote, p. 58

protist, p. 59


▶ Reading SkillClassify and Categorize

What are microscopic

organisms?Microscopic organisms are found everywhere.

They live and grow on every surface in the world. Some are producers, which can make their own food by photosynthesis. Others are consumers, which eat other organisms for food. Some are decomposers, which break down and consume dead organisms. Microorganisms are an important part of Earth’s ecosystems. They provide larger organisms with some of the food and oxygen they need to survive. They help enrich the environment by breaking down dead organisms.

What parts of the microscope would you use to change the focus?

Clue: Look at the diagram, and read the labels.

Reading Diagrams

56EXPLAIN


Studying Microscopic Organisms

A microscope is an instrument that produces an enlarged image of an object. Anton van Leeuwenhoek (AN•ton•vahn•LAY•ven•hook), a Dutch merchant, used a microscope to study microscopic organisms in the 1600s. His tool was very simple, but scientists today have more-powerful microscopes that enable them to see microscopic organisms in much greater detail.

Scientists study living and nonliving microscopic organisms with an instrument called a compound light microscope. A compound light microscope uses two or more lenses and a light source to magnify objects. The lens on the bottom of the microscope’s body tube is the objective lens. The lens at the top of the body tube, nearest your eye, is called the ocular lens.

Samples placed on the stage of the microscope are first magnified by the objective lens. The image that reaches the ocular lens is then magnified again. For example, the objective lens of a microscope magnifies an object 200 times (200x) and the ocular lens magnifies it 10 times (10x). If these two magnifications are multiplied together, then the overall magnification is 2,000 times (2,000x) (200 × 10 = 2,000). Images begin to get blurry at magnifications higher than 2,000x.

Scientists study very small, nonliving organisms and other objects with an electron microscope . This is a powerful microscope that uses a beam of electrons, rather than a light

source, to magnify samples. Electron microscopes cannot be used on living samples, because the stream of electrons and the preparation process would kill them. The most commonly used electron microscope is called a scanning electron microscope, or SEM. The SEM can magnify as much as 300,000 times (300,000x). It scans the surfaces of nonliving samples and gives detailed three-dimensional images of them.

▲ Scanning electron microscopes produce magnified images, such as this picture of bacteria found on the human tongue.

Quick Check

Classify and Categorize Describe

the different kinds of microscopes.

Which do scientists use to study

living organisms?

Critical Thinking Explain why

scientists do not use electron

microscopes to study human

subjects.

57EXPLAIN

Microscopic organisms are classified in two ways: by their cell structure and by what they eat. The cell structure determines whether they are prokaryotes (pro•KEH•ree•ohtz)

or eukaryotes (yoo•KEH•ree•ohtz). Prokaryotes have a simple cell structure without a nucleus in each cell. Eukaryotes are more complex organisms that do have a nucleus in each cell. Within each of these two groups, there are organisms that eat other organisms (consumers) and those that can make their own food (producers).

Producers make food by using the energy in sunlight for photosynthesis. Green plants use photosynthesis to make their own food and release oxygen. However, green plants are not the only organisms that carry out photosynthesis. Many microscopic producers make their own food and give off oxygen.

Microscopic organisms that produced the oxygen that first made Earth inhabitable for other living things were prokaryotic producers, such as cyanobacteria (SIGH•an•oh•bak•teer•ee•uh). They can be found in many places, including fresh and salt water, hot springs, and the Arctic. Today cyanobacteria and other photosynthetic microscopic producers produce about half of our oxygen supply. Without these organisms plants and trees alone would not be able to support life on Earth.

▼ Cyanobacteria often form a chain of cells called a filament. These chains can produce different kinds of algae.

What are microscopic organisms

that make their own food?

58EXPLAIN

Protists

Another kind of microscopic organism is a protist. A protist is a single-celled, eukaryotic organism that cannot be clearly classified as animal or plant. Many protists are capable of producing their own food through photosynthesis, like plants. Others eat microscopic organisms.

One example of a photosynthetic protist is a diatom. Diatoms live in either salt water or fresh water. These protists are very small and have shapes such as straight lines, circles, or squares. Because there are so many diatoms living in lakes and oceans, they are some of the most important producers of oxygen and are a major food source for many other organisms.

Another kind of protist is a dinoflagellate (dighn•uh•FLAJ•uh•luht). A dinoflagellate has characteristics of both plants and animals. Some

species of dinoflagellates can light up like fireflies. When stirred up, they give off light and make the ocean appear to glow in the wakes of passing boats. Most dinoflagellates are photosynthetic and make up a significant part of the phytoplankton, or photosynthetic microorganisms that float in oceans and lakes. They are also important oxygen producers and a major food source.

Quick Check

Classify and Categorize How

do scientists classify microscopic

organisms that have characteristics

of both plants and animals?

Critical Thinking How are

cyanobacteria different from

plantlike protists?

dinoflagellatediatoms

59EXPLAIN

Some microscopic organisms are not able to make their own food. Instead, they need to find food in their environment. They must be able to move to where food is. To do this they have developed structures on the outsides of their cells that help them move and eat.

One protist of this type is a protozoan. Protozoans have no cell walls and can find and eat food. Examples of protozoans include flagellates (FLAJ•uh•latz) and ciliates.

Flagellates are protozoans that have flagella (fluh•JEL•uh), or long, hairlike structures that whip and lash to help them swim. Some flagellates live in ponds and lakes, feeding on smaller organisms. Many others are parasites, which means that they feed off and harm other organisms.

All protists that have small, hairlike projections, or cilia, extending from the outsides of their cells are called ciliates. These organisms use the cilia as oars to move themselves through water. Ciliates also use their cilia to direct bacteria and other food from their environment into a food vacuole. A food vacuole is a structure inside a cell that stores food.

Other Traveling Protists

Another group of protists has pseudopods (SOO•doh•podz), or “false feet.” This group of protists includes hundreds of species of amoebas. Found in fresh water, salt water, and soil, amoebas use their pseudopods to pull themselves in the direction in which they want to move. They also use their pseudopods to eat. An amoeba will extend a false foot and wrap it around what it wants to eat. When the end of the pseudopod meets the amoeba’s body, both the foot and the food become part of the body. Once the food is inside the amoeba, it gets wrapped in a food vacuole to be digested.

What are microscopic organisms

that cannot make their own food?

▶ Scientists use scanning electron microscopes to study microorganisms.

60EXPLAIN

Protozoans

▲ The most common example of a ciliate is the paramecium. Tiny surface hairs enable it to move.

▲ A euglena can make its own food or eat food from the environment. A flagellum helps it move.

Observing Protists

Slide a metric ruler onto the stage of your microscope, and focus on it, using the highest power. Measure the field of view, and record your measurement in millimeters.

Obtain a pond-water sample from your teacher. Put a drop of the water in the center of a microscope slide. Gently place a coverslip over it.

Observe Starting with the lowest power, focus the microscope until you find microorganisms. Switch to high power, and focus. Draw what you see.

Measure Estimate how much area one microorganism you are observing takes up. Multiply that number by the size of your field of view to estimate the size of the organism in millimeters. For example, 1

3 × 1

2 mm = 1

6 mm.

Quick Check

Classify and Categorize How are

microscopic consumers grouped?

Critical Thinking How do

microscopic consumers get to

their food?

paramecium magnified 100 times

euglena magnified 130 times

amoeba magnified 30 times

▲ An amoeba moves by forming thick extensions, or pseudopods. As a pseudopod is thrust forward, the rest of the amoeba flows with it.

Which protozoan is the smallest? The largest?

Clue: Read the label that tells how many times each protozoan was magnified.

Reading Photos

61EXPLAIN

What roles do microscopic

organisms have in ecosystems?Microscopic producers make their own food through

photosynthesis. As a result of that process, they give off about half of the oxygen in our atmosphere. However, microscopic consumers cannot make their own food. As a result they eat other microscopic organisms.

Both microscopic producers and microscopic consumers are the main food source for larger consumers. There are also microscopic organisms that feed on dead organisms of all sizes. These organisms are called decomposers, and their job is to recycle organic materials back into the food chain. This cycle of what eats what becomes the first set of links in a food chain that extends from the tiniest organisms all the way to humans.

Quick Check

Classify and Categorize What are the

three roles of microscopic organisms?

Critical Thinking What would happen if

all organisms could make their own food?

lake ecosystem

▼ These mushrooms help recycle the log.

62EXPLAIN

Write a NarrativeWrite about one of the microorganisms

that you have learned about. Describe

what its life is like. What does it look

like? How does it move? Does it have

any enemies?

Determine MagnificationIf the objective lens on a microscope

magnifies an object 100 times (100x),

and the ocular lens magnifies it

10 times (10x), what is the overall

magnification?



Microscopes are tools that produce enlarged images of objects.(pp. 56–57)

Microscopic organisms that produce food include cyanobacteria, diatoms, dinoflagellates, and euglenas.(pp. 58–61)

Microscopic producers form the foundation for most food chains in the oceans and in freshwater ecosystems.(p. 62)

Think, Talk, and Write Main Idea Matter and are transferred from one organism to another at the microscopic level.

Vocabulary A(n) produces an enlarged image of an object.

Classify and Categorize What is the major difference between eukaryotes and prokaryotes?

Critical Thinking Why are protists hard to identify as plants or animals?

Test Practice Which organisms use pseudopods to move?A amoebasB euglenasC cyanobacteriaD diatoms

Test Practice Which organisms live in either salt water or fresh water?A flagellaB ciliaC diatomsD protozoans

Make a Study GuideMake a three-tab book (see pp. 487–490). Use the titles shown. On the inside of each tab, write several sentences that classify and categorize each of the topics.



What do museums do when their artwork and other cultural artifacts are being slowly eaten by organisms they can’t even see? They turn to scientists like Maria Pia Di Bonaventura at the American Museum of Natural History. Maria Pia is not a detective, but she knows how to unlock mysteries like these, where the main suspects are microorganisms such as fungi and bacteria.

Maria Pia helped an art museum take a microscopic look at several paintings. Paintings made of wood, ink, oils, and canvas can be perfect environments for some microorganisms to grow in. You may not be able to see them with your eyes, but they give themselves away by their green, blue, and yellow tints and the black markings they leave behind.

▶ Maria Pia is a microbiologist. That’s a scientist who studies microorganisms and their effects on other organisms.

ELA R 6.2.3. Connect and clarify main ideas by identifying their relationships to other sources and related topics.64

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Meet a Scientist

Write About ItMain Idea

1. Why do museums ask for help from scientists like Maria Pia Di Bonaventura?

2. How does Maria Pia’s work help protect works of art and other artifacts?


Main Idea

▶ Look for the question or problem being discussed.

▶ Think about how the details relate to each other.

To study the microorganisms that are making their home in the art, Maria Pia first takes a sample of them. Back in the lab, Maria Pia focuses on the fungi. She grows them to find out more about their DNA. The DNA provides the information that Maria Pia uses to determine the species of the fungi. The different species respond to different treatments, so after she identifies a species, she can figure out the best way to protect the paintings from its damage.

Fungi don’t just live on paintings. They live in all kinds of environments on our planet, in the tropical rain forests and the cold tundras, in the rivers and the oceans, and even in deserts! Maria Pia is interested in investigating their amazing diversity—there are over 100,000

species of fungi, and more are being discovered all the time. In fact, the world’s largest known organism is thought to be a fungus weighing over 100 tons, about the weight of an adult blue whale!

▲ Fungi grew on and damaged this artwork.

65EXTEND


Lesson 4

Earth’s Food Chains, Webs, and Pyramids

Whales are among the largest animals ever to have lived on Earth. What do such large animals eat? Surprisingly, many of them eat some of the smallest organisms in the ocean: tiny shrimplike animals called krill. A humpback whale eats as much as 1,360 kilograms (3,000 pounds) of krill, plankton, and small fish each day.

6 LS 5.b. Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment. • 6 LS 5.c. Students know populations of organisms can be categorized by the functions they serve in an ecosystem.66

ENGAGE

Materials

Make a PredictionWhat would a food chain of 20 organisms look like? Would it be linear? Write your answer as a prediction in the form “If 20 animals were made into a food chain, then it would look like . . .”


Cut construction paper into 20 rectangles. Write the names of eight producers, six animals that eat the producers, four animals that eat the plant eaters, and two animals that eat the animals that eat the plant eaters. Make a hole in each rectangle.

Make a Model Cover the top of the soda bottle with construction paper. This will be the Sun. Punch eight holes around the rim. Attach a piece of yarn to each of the eight producers. Attach the other ends to the soda bottle. Using yarn, link each plant-eating animal to a producer. Continue by linking the animals that eat the plant eaters to the plant-eating animals. Only one animal may be attached to a food source.

Draw Conclusions

Observe How many levels are in your model? What happens to the number of organisms in each level as you move away from the Sun?

Predict What would happen to the number of plant eaters if a drought destroyed the plants? What happens to the animal populations?

• top half of empty soda bottle

• yarn

• construction paper

• hole punch

• scissors

What changes might occur in an ecosystem into which the predators move? Make a prediction and test it. Then analyze and present your results.

Explore More

Step

How can you model a food chain?

6 IE 7.d. Communicate the steps and results from an investigation in written reports and oral presentations.

67EXPLORE

cattle grazing, Big Sur, California


Energy and matter are transferred from one organism to another in food chains and food webs.

▶ Vocabularyproducer, p. 69

consumer, p. 69

decomposer, p. 69

food chain, p. 70

primary consumer, p. 71

secondary consumer, p. 71

tertiary consumer, p. 71

food web, p. 72

herbivore, p. 72

carnivore, p. 72

omnivore, p. 73

predator, p. 73

prey, p. 73

scavenger, p. 73

energy pyramid, p. 76


▶ Reading SkillCompare and Contrast

What are producers, consumers,

and decomposers?Think about how food is arranged at the

grocery store. There are sections for baked goods, meats, produce, and dairy products. How do you think each of the food groups would fit into an ecosystem? Energy in many ecosystems begins with the Sun and is transferred from one organism to another. Each living thing has a role in this process.

Producers

Think of the last time you went to the grocery store. What did you see in the produce section? You saw producers—fruits and vegetables. The grains used to make the bread in the bakery aisle are producers, too.

Explore food webs with a park ranger. Explore energy pyramids with a farmer.

▲ These cattle get their energy directly from the grass, which is a producer. How would you classify the cattle? They are consumers.

68EXPLAIN


Producers , such as plants and algae, are organisms that use energy from the Sun to make their own food. They also produce oxygen and food that other living things need to survive. Most producers on Earth live near the surface of the ocean, where tiny photosynthetic organisms carry out more than 70% of the photosynthesis that occurs on Earth. Green plants are among the producers that live on land.

Consumers

If an organism cannot create its own food, it must directly or indirectly consume, or eat, other organisms. Consumers get energy by feeding directly on producers or by eating animals that feed on producers. If you eat fish, chicken, or beef, you are indirectly getting energy from a producer. The steer that is now a steak either grazed on grass or was fed a mixture of grains.

Decomposers

Decomposers break down dead organisms into simpler substances. Some of these substances are absorbed by the decomposers. Others are returned to the environment. This is one reason why decomposers are an important part of an ecosystem.

Elements that are essential to life, such as oxygen, nitrogen, and carbon, are building blocks of living things. When decomposers do their jobs, they recycle these and other important substances back into the environment. In the process they clean up the environment by ridding it of waste matter. Earth’s decomposers include worms, bacteria, fungi, and insects.

Quick Check

Compare and Contrast What are

the main differences among producers,

consumers, and decomposers?

Critical Thinking How do consumers

get the energy they need to survive?▼ These mushrooms are

returning important substances to the environment by breaking down the stump of a maple tree.

69EXPLAIN

What is a food chain?A food chain shows how energy

flows from one organism to another in an ecosystem. In a food chain, producers absorb the Sun’s energy before passing it on to consumers and decomposers. The path by which the energy travels can be short and simple or long and complicated.

What does a food chain look like? Is it arranged by size, from the largest organism to the smallest? Do larger organisms always consume organisms of a slightly smaller size? This is not always the case. Remember the humpback whale? It eats krill, some of the smallest animals in the sea. Cougars, on the other hand, sometimes prefer to prey on animals larger than themselves, such as moose and elk.

Forest Food Chain

What is the path of energy in this forest food chain?

Clue: Follow the arrows.

Reading Diagrams

▲ The zebra and the lion are part of a food chain.

70EXPLAIN

Links in the Food Chain

Consumers can be classified by where they fall on the food chain. Primary consumers , which are organisms that eat producers, are the second link in a food chain after producers. On land, primary consumers include insects, mice, rabbits, horses, and elephants. The size of the animal does not always determine its diet or its location on the food chain.

The organisms that get their energy by eating primary consumers are called secondary consumers . Secondary consumers make up the third link in a food chain. Many birds, for example, are secondary consumers, because they eat insects that feed on plants. A snake that eats such a bird is a tertiary consumer . A tertiary consumer is usually the top predator in a food chain. There are usually many producers and few tertiary consumers.

What happens to an organism that is not eaten? If an organism is not eaten, it will eventually die. Decomposers are present throughout the food chain to break down the remains of dead plants and animals.

The remains of these plants and animals break down into nutrients that producers use. This completes the cycle and allows another food chain to begin. The amount of energy present decreases as it travels through each organism, but it never completely disappears. Some of the energy is used for life processes, and some is given off as heat, but it never completely disappears.

Quick Check

Compare and Contrast How do

people fit into the food chain?

Critical Thinking Compare primary,

secondary, and tertiary consumers.

Your Food Chain

Keep a log of everything you eat for one day.

Classify For each food, determine whether it is a producer or a consumer.

Classify Which foods did you list as producers?

Classify Which foods did you list as consumers?

Communicate Select two foods from the consumer group, and draw a possible food chain for each. Do not forget to include yourself. Did you include decomposers in your food chain? Where do they fit?

71EXPLAIN

What is a land food web?Do you eat only one kind of food?

If you are like most people, you enjoy a variety of foods. In nature most organisms would not survive if they fed on only one type of food.

A food chain represents only one thing that each consumer may eat. It shows only one path that the energy follows from the Sun through the food chain. A food web shows all the food chains in an ecosystem and shows how they overlap. Food webs also show the roles and relationships among all the species in an ecosystem.

Herbivores

Just like food chains, all food webs begin with producers. Herbivores are primary consumers, or animals that eat producers. On land, herbivores have flat-edged teeth in the fronts

of their mouths for tearing plant material. Their flattened back teeth are perfect for grinding the plants to a pulp. Many ocean-dwelling animals are filter feeders. Some filter feeders use modified teeth, called baleen, to filter out small organisms from huge mouthfuls of water.

Carnivores

Carnivores are secondary and tertiary consumers, animals that eat other animals. Some carnivores rip into prey with their sharp incisors and canine teeth or with their beaks. They typically eat more than one kind of animal. For example, coyotes eat a variety of small mammals as well as birds and snakes. Cats will eat fish and other animals. The golden eagle preys upon a variety of animals, including prairie dogs, rabbits, and ground squirrels.

Land Food Web

A food web is a series of overlapping food chains. It is a more accurate representation of the feeding relationships in an ecosystem than a food chain, because most animals eat more than one thing.

72EXPLAIN

Omnivores

Animals that eat both producers and consumers are omnivores . Many animals, including humans, are omnivores. Raccoons will eat fruits, nuts, grains, birds’ eggs, young rabbits, rodents, fish, turtles, and even scraps from your garbage.

Predators

Living things that hunt and kill other living things for food are predators . The animals they hunt are prey . Most animals, at one time or another, will be both predator and prey. A snake can eat a mouse one day and find itself as prey for a hawk the next day.

Scavengers

Have you ever been on a scavenger hunt? It is a game in which you have to find items. In the same way, scavengers seek out the remains of dead animals to eat. They eat meat without hunting or killing the prey. Jackals, vultures, and crows are scavengers. Fungi are another type of scavenger. Fungi such as mushrooms get their energy from decaying plants and animals.

Which of these animals are predators? Which are prey?

Clue: Follow the arrows on the diagram to see which animals prey on others.

Reading Diagrams

Quick Check

Compare and Contrast What

is the difference between a food

chain and a food web?

Critical Thinking Which roles in

a food web could people play?

▲ The California condor is a large scavenger.

73EXPLAIN

Just like land food webs, marine food webs begin with producers. In the ocean, phytoplankton are the primary producers. Because phytoplankton depend on sunlight to carry out photosynthesis, the size of their populations depends on the amount of sunlight that penetrates the water. Oceans are divided into different areas depending on the amount of sunlight they receive and the temperature of the water.

Intertidal Zone

The intertidal (in•tur•TIGH•duhl) zone is the area of the ocean at the edge of the land. This area is affected

by changes in high and low tides. Despite the harsh conditions found at the ocean’s edge, the intertidal zone supports a variety of living things. Each time the tide comes in, the plants and animals that live there are submerged in water. At low tide they are exposed to air and sunlight.

Some parts of the intertidal zone are covered by water only during the highest tides. Only a few species of algae and mollusks are found there. Areas that are underwater during high tide contain algae and animals such as snails, crabs, sea stars, and small fish. These are food sources for many land and sea creatures as well as shorebirds.

red knots

What is a marine food web?

74EXPLAIN

Ocean Zones

From just beyond the low-tide line to the point where the open ocean begins is an area where sunlight penetrates and waters are calmer. There you will find some of the world’s most magnificent underwater habitats. For example, the giant kelp forests off the California coast provide food and shelter to hundreds of species of fish, invertebrates, marine birds, and marine mammals. This is a region of complex food webs with predators such as sea lions and harbor seals and many types of prey at every feeding level.

In the open ocean, most organisms live in three main zones. The top, or sunlight, zone reaches from the surface down to about 200 meters (656 feet). Plankton live near the surface, where the sunlight penetrates the water. Squid, octopuses, whales, fish, and many other organisms feed on the plankton.

Between about 200 meters (656 feet) and 1,000 meters (3,280 feet) there is little light. This zone, the twilight zone, is dark and cold, with little food available. Animals that live in this zone have adaptations for these harsh conditions. The third zone down has no light and is called the midnight zone. No photosynthetic organisms grow here, and some animals are eyeless.

▲ Sea otters find shelter and food in the diverse kelp-forest community.

Quick Check

Compare and Contrast What are

the differences among the three

main zones in the open ocean?

Critical Thinking What do land

food webs and marine food webs

have in common?

75EXPLAIN

How are populations

connected?Food chains and food webs

show how energy flows through an ecosystem. What they do not show is how energy is lost as it passes from producers to consumers to decomposers. Energy pyramids are models that show how energy moves through a food chain. Producers always make up the base of the pyramid. At each feeding level above the base, energy is lost. When animals eat, they cannot absorb all the energy their food contains. Organisms also lose energy when they perform their daily activities. Think about the energy you use each day. As energy is used, it is transferred to the environment as heat.

Energy decreases from the base of the pyramid to the top. About 10% of the energy at one level can be used by animals at the next level. With less and less energy available at higher levels, fewer animals can survive. Are there more producers or consumers in the world? The decrease in energy limits the number of consumers on the food chain, so there are more producers.

Anything that happens in an ecosystem can upset the balance of food and energy. As long as populations in a community can obtain the food, water, and shelter they need, they can reproduce and grow as a species. If something happens to decrease any of these resources, competition may increase within the community. This can cause the population of a species to decrease or even to become extinct. On the other hand, the species might adapt to change or migrate to new areas. Knowing about food chains and food webs helps scientists predict how communities will be affected by change.

Quick Check

Compare and Contrast What do the

layers of an energy pyramid show?

Critical Thinking What would

happen if resources decreased

in a location?

▶ ocean energy pyramid

76EXPLAIN



-Review Summaries and quizzes online @ www.macmillanmh.com

Think, Talk, and Write Main Idea Food chains show how

and are transferred.

Vocabulary A(n) eats the remains of dead animals it finds.

Compare and Contrast How is a scavenger different from a decomposer?

Critical Thinking Explain why a food web tells us more about an ecosystem than a food chain.

Test Practice Which of the following is not a group into which organisms are classified in an ecosystem?A producersB decomposersC consumersD energy pyramids

Test Practice What are living things that hunt and kill other living things for food?A herbivoresB predatorsC fungiD scavengers

Producers use energy from the Sun to make their own food. Consumers get their energy from producers.(pp. 68–69)

A food chain shows the flow of energy from one organism to another in an ecosystem. (pp. 70–71)

A food web shows all the food chains in an ecosystem and how they overlap.(pp. 72–75)

Make a Study GuideMake a three-tab book (see pp. 487–490). Use the titles shown. On the inside of each tab, compare and contrast the role of each topic with others in the lesson.

Persuasive WritingResearch an issue that affects Earth’s

ecosystems. Then write and record a

public-service announcement to state

your position on the issue.

Use PercentsAn energy pyramid shows that

90% of the energy is lost from one

level to the next. If you start with

100,000 units of energy, how much

energy does the next level get?

77EVALUATE


Have you ever seen an eagle, a hawk, or an owl swoop down and capture its food? These birds of prey, or raptors, are at the top of their food chain, because they have few predators. Their bodies are amazing flying machines that enable them to attack quickly and fly away with their prey.

Raptors have strong, sharp beaks and large wings. Their wings help them soar and swoop down on their prey, which they capture in their talons, or claws. Raptors’ wingspans (the distance from the tip of one extended wing to the tip of the other) are far longer than their bodies.

The table on the next page shows the lengths of some raptors’ bodies and their corresponding wingspans. Look at the data, and complete the table by finding the ratio of body length to wingspan in decimal form. Then place these decimals on a number line to determine which bird has the smallest body in relation to its wingspan.

Finding ratios

To find the ratio of body length to wingspan,

▶ divide the body length by the wingspan.

bald eagle: 80 ÷ 200 = 0.40

(expressed as a fraction:

expressed as a percent: 40%)

80200

= 8

20 =

25

Why Are They at the Top of Their Food Chain?

78EXTEND

Solve It 1. Which bird’s body length is half of its wingspan?

2. If a raptor’s wingspan were 112 centimeters, how long would its body have to be for it to have a body-to-wingspan ratio of 0.45?

3. Use a tape measure to determine the ratio of your arm span to your body length. Will everyone in your class have the same ratio? Why or why not?

BirdBody length

(in centimeters)Wingspan

(in centimeters)Ratio of bodyto wingspan

Bald eagle 80 200 0.40

White-tailed hawk 50 120 0.44

Gray hawk 38 89

Swainson’s hawk 46 124

Sharp-shinned hawk 27 54 0.50

Long-eared owl 33 99

Golden eagle 81 198

Cooper’s hawk 39 71 0.55

Number Line

0.30 0.40 0.50 0.60

MA NS 6.1.2. Interpret and use ratios in different contexts (e.g., batting averages, miles per hour) to show the relative sizes of two quantities, using appropriate notations (a/b, a to b, a:b).

79EXTEND

Lesson 5

Earth’s Cycles for Life

Water covers about 75% of Earth’s surface. Did you ever wonder where all this water comes from? Could the water in your shower be from the same stream that a lion once drank from?

6 LS 5.b. Students know matter is transferred over time from one organism to others in the food web and between organisms and the physical environment.80

ENGAGE

Materials

• empty soda bottle with cap (cut into halves)

• soil

• water spray bottle

• lamp or window with sunlight

How does water recycle itself?

Make a PredictionAll living things rely on water, yet there is a limited supply of water on Earth. Water is recycled so that it can be used again and again. What will happen to soil if it is moistened with water and then placed under a heat source? Write your answer as a prediction in the form “If moistened soil is allowed to sit under a heat source, then the water in the soil will . . .”


Place about 4 inches of soil in the bottom half of the soda bottle.

Spray the soil with water so that it is moist but not wet.

Secure the top half of the soda bottle over the bottom half. Use tape if necessary.

Observe Place the bottle under a lamp or in direct sunlight. Observe it every 10 minutes for a class period. Write down your observations. Observe the bottle again on the second day. Write down your observations.

Draw Conclusions

What did you see the first day? What did you see the second day?

Infer What was the source of the water? What was the source of the energy that caused changes in the bottle?

Observe What happened to the water?

What might happen if you added some small plants to the bottle? Some small rocks? What might happen if you added more heat or placed the bottle in the shade?

Explore More

Step

Step

6 IE 7.e. Recognize whether evidence is consistent with a proposed explanation.

81EXPLORE

precipitation

The Water Cycle

How does Earth have enough

air and water to keep us alive?You know that people recycle bottles, cans,

and newspapers to help the environment. Did you know that the environment recycles itself, too? The air people breathe and the water people drink do not run out, because the planet is always recycling them.


Earth recycles water and other substances, such as carbon and nitrogen.

▶ Vocabularywater cycle, p. 83

evaporation, p. 83

condensation, p. 83

precipitation, p. 83

carbon cycle, p. 84

nitrogen cycle, p. 86

nitrate, p. 87

nitrite, p. 87

composting, p. 88


▶ Reading SkillMain Idea

82EXPLAIN


Golden Gate Bridge, San Francisco, California

The Water Cycle

A cycle is a series of events that happen one after another, in the same order, over and over again. Think about a bicycle. Why do you think it is called that? It has two wheels (bi-) that go around and around (-cycle).

The water cycle is the continuous movement of water between Earth’s surface and the air. The water cycle works because water can change from a solid to a liquid to a gas and back again. The energy from the Sun powers the water cycle.

The Sun heats the water in oceans, lakes, rivers, ponds, and puddles. This causes evaporation , the process in which a liquid changes into a gas. As the water vapor moves higher into the atmosphere, it cools and condenses into tiny water droplets. Condensation is the process in which a gas changes into a liquid. Condensation causes water to form on the outside of a cold glass of lemonade on a hot day.

Droplets of condensed water accumulate in clouds. When the droplets become too heavy, they fall

to Earth’s surface. Precipitation is any form of water—rain, snow, sleet, or hail—that falls to Earth.

When water hits Earth’s surface, it may soak into the ground and be stored as groundwater, in a process called collection. It may also run across the surface and be collected in streams, ponds, lakes, oceans, or other bodies of water. Some of this collected water evaporates back into the atmosphere.

About 85% of the water that evaporates on Earth comes from the ocean. Most of this water quickly condenses and falls back into the ocean. Water evaporates from both freshwater and saltwater sources. However, all of the precipitation that falls on Earth is fresh water. The salt is left behind when salt water evaporates.

condensation

Quick Check

Main Idea What form of water does

condensation produce, a liquid,

a solid, or a gas?

Critical Thinking What is the order

of the four parts of the water cycle?

83EXPLAIN

What is the carbon cycle?Carbon is one of the elements that make up all living

things. Plants and animals (including people) need carbon to live. There is not a lot of carbon in the atmosphere, so it must be recycled. Otherwise it would be used up too quickly. The process in which carbon is recycled between the atmosphere and living things is called the carbon cycle .

There is evidence that a buildup of gases such as carbon dioxide, nitric oxide, and methane trap heat that normally would escape from Earth’s atmosphere. Called the greenhouse effect, this buildup raises temperatures and leads to global warming.

Since 1850 the average temperature on Earth has risen about 1.8°F (1°C ). Some scientists predict it will rise 3.5°F (2°C) by the year 2100. They believe this rise will lead to many problems, such as the melting of the polar ice caps, which would cause sea levels to rise and flood coastal areas.

The Carbon Cycle

Plants During photosynthesis, plants use the carbon from carbon dioxide to make sugars, starches, and proteins. They also give off oxygen, which is used by animals.

Death and decay When living things die, the carbon in them goes into the air and the ground. Some of it is turned into carbon dioxide by the organisms that feed on dead organisms.

Carbon enters the air in three ways: when plants and animals decay; when animals breathe out (exhale); and when fossil fuels such as coal, oil, gasoline, and natural gas are burned.

84EXPLAIN

What happens to carbon when living things die?

Clue: Read the text boxes.

Reading Diagrams

Carbon and Life

Carbon is stored in molecules of living and dead organisms, in organic matter in soil, in the air as carbon dioxide, and in fossil fuels. Dissolved carbon dioxide is also found in the ocean and in the shells of some marine organisms.

Plants and other photosynthetic organisms take in carbon dioxide and water and use them to make food. During this process, oxygen is released into the atmosphere as a waste product. When living things need to use the energy that has been stored in food, they use oxygen to break apart

the molecules during respiration. The final products are energy, water, and carbon dioxide. The carbon dioxide is returned to the atmosphere, continuing the cycle.

Quick Check

Main Idea Why is the carbon

cycle important to living things?

Critical Thinking Where does

the carbon that has been stored

in an animal’s body go when the

animal dies?

Animals Animals eat plant sugars, starches, proteins, and other substances. The animals use the carbon in these foods to make their own body chemicals.

Storage Some carbon is stored as fossil fuels. This is the carbon left behind by certain organisms that died millions of years ago.

85EXPLAIN

The Nitrogen Cycle

from nitrogen compounds in the soil that have been made usable. Animals then get nitrogen in the same way they get energy—by eating plants or by eating the animals that eat the plants that absorb the nitrogen.

Uses of Nitrogen

Lightning can change the nitrogen found in the atmosphere into a water-soluble compound that dissolves in rainwater to form nitric acid. A small amount of nitrogen is absorbed into soil this way.

The rest of the nitrogen in soil comes from bacteria. Certain bacteria, called nitrogen-fixing bacteria, live in

All living things must have nitrogen to develop and grow. Nitrogen is needed to make proteins, which are the building materials for muscles, skin, bones, blood, plants’ cell walls, and internal organs. Just like water and carbon, nitrogen is cycled through the environment.

The nitrogen cycle is the continuous trapping of nitrogen gas into compounds in the soil and the returning of nitrogen gas to the air. Earth’s atmosphere is 78% nitrogen. You would think this would be enough to supply living things with the nitrogen they need. However, plants and animals cannot use nitrogen in this form. Plants must get nitrogen

What is the nitrogen cycle?

nitrogen gas

nitratesnitrites with

ammonianitrites

86EXPLAIN

the roots of beans, peas, and peanuts and can extract nitrogen from the air. Other bacteria convert this nitrogen into usable compounds called nitrates and nitrites . Plants absorb the nitrates and nitrites and use them to make proteins. These proteins are passed along when animals eat plants and one another.

When plants and animals die, nitrogen from their remains returns to the soil when bacteria break it down into nitrogen gas. These bacteria return about the same amount of nitrogen to the air as other bacteria take from the air, keeping nature in balance.

Quick Check

Main Idea What is the nitrogen

cycle?

Critical Thinking Why do some

people use manure, or raw animal

wastes, in their gardens?

Fertilizers

Fill two plastic cups with pond water or water from an aquarium.

Add a few water plants, such as elodea, to each cup.

Add a teaspoon of houseplant food to one cup, and label the cup. Be Careful. Always wear protective gloves when handling plant foods.

Observe Place both cups in a sunny window, and observe them each day for a week. Record your observations.

Interpret Data What effect did the plant food have on the plant growth in the cups? What is the independent variable in this lab? What is the dependent variable?What role do decomposers

play in the nitrogen cycle?

Clue: Where do plants obtain nitrogen from?

Reading Diagrams

nitrogen compounds

87EXPLAIN

How are plants recycled?Plants are necessary to each

of nature’s cycles. Plants continue their work even after they die. Think of a giant tree falling in a forest. Right away it becomes a habitat for many different animals, including birds, frogs, and insects. Soon after it falls, the tree begins to break down.

Decomposers are organisms that break down dead plants and animals into useful things such as minerals and rich soils. Plants need these in order to grow. As you can see, each kind of organism has a role that helps others survive. Worms, crickets, cockroaches, bacteria, and fungi are decomposers. These organisms help plants survive.

Composting

What happened to the fallen tree also applies to your yard and some of the food scraps around your home. Certain kinds of scraps from the food you eat or cuttings from your yard still contain nutrients and other substances that can be recycled. Composting is the process in which decomposers break down organic matter so it can be used as a natural fertilizer for gardening or farming. You can make compost by mixing three parts dry leaves and plant material, one part fresh grass clippings, and one part vegetable food scraps. Decomposers soon go to work, breaking down these materials into nitrogen and other elements that make the soil rich.

composting

Quick Check

Main Idea What is the role of

decomposers in an ecosystem?


first thing that happens when

a tree dies and falls down?

▼ The yellow coral fungus helps break down this fallen tree.

88EXPLAIN


The water cycle is the continuous movement of water between Earth’s surface and the atmosphere. (pp. 82–83)

The carbon cycle is the process in which carbon moves between the atmosphere and living things.(pp. 84–85)

The nitrogen cycle is the movement of nitrogen among air, soil, plants, and animals.(pp. 86–87)

Make a Study GuideMake a three-tab folded book (see pp. 487–490). Use the titles shown. On the inside of each tab, write two sentences about the main idea of the topic.

Critical Thinking What would happen if Earth became much warmer?

Test Practice Which of the following objects would most likely take the longest to decompose?A plastic bottleB eggshellC paper bagD schoolbook

Test Practice What is the process in which a liquid changes into a gas?A precipitationB evaporationC condensationD collection

Think, Talk, and Write Main Idea Earth water, carbon, and nitrogen.

Vocabulary The process in which a gas changes into a liquid is .

Main Idea What happens to the nitrogen compounds that are not absorbed by plants?

Expository WritingResearch a local environmental

problem that is related to water or air.

How does this problem result from

human activities?

Estimate Fresh WaterOf Earth’s fresh water, 69% is polar

ice, 30% is groundwater, and 0.9%

is permafrost. What percent of

Earth’s fresh water is available for

use by people?

Math LinkWriting Link



MaterialsInquiry Structured

What factors affect the carbon,

water, and nitrogen cycles?

Form a HypothesisThe carbon cycle is a series of events that recycles carbon through the environment. Carbon exists in many forms and can be found in the air and in plants and animals. Plants take in carbon dioxide from the air and convert it into food and oxygen. The amount of carbon found in the air is affected by air pollution, especially pollution from the burning of fossil fuels. What role do plants play in the carbon cycle? Write your answer as a hypothesis in the form “If carbon dioxide is added to a system containing a plant, then . . .”

Be Careful. Wash your hands with soap and water after the investigation. Immediately wash any area of skin that comes in contact with bromothymol blue.

elodea

graduated cylinder

Step

Step

Step


Use a straw to blow slowly into a small cup of bromothymol blue. Record your observations in your journal.

Be Careful. Be sure to breathe out through the straw. Do not breathe in. Do not drink the liquid in the cup.

Measure Pour 10 milliliters of bromothymol blue into a test tube. Record the color of the liquid in your journal.

Experiment Use a straw to blow gently into the test tube until the liquid turns light green. Place one piece of elodea in the test tube, and put the cap on the tube.

Place the test tube in a rack near a window, and check the color of the bromothymol blue every 30 minutes for 2 hours. Record the color of the liquid at each interval.

bromothymol blue

test tube with cap

straw

small cup

6 IE 7.a. Develop a hypothesis.90EXTEND

Ask a Question

Form a Hypothesis


Draw Conclusions

Draw Conclusions

Explain What made the bromothymol blue change color in step 1?

Analyze If you had continued blowing into the test tube instead of capping it, what do you think would have happened during the 2-hour experiment?

Infer What part of the carbon cycle did you represent when you blew into the test tube?

Inquiry Guided

What factors affect the water cycle?

Form a HypothesisDoes temperature affect the water cycle? Write your answer as a hypothesis in the form “If the average air temperature changes over a long period of time, then the water cycle will . . .”

Test Your HypothesisDesign an experiment to investigate how temperature affects the water cycle. Write out the materials you need and the steps you will follow. Record your results and observations.

Draw ConclusionsDid your results support your hypothesis? Why or why not? What do you think would happen to the water cycle in a large land area if volcanic ash blocked the Sun’s rays for a few months?

Inquiry Open

What can you learn about the nitrogen cycle? For example, does pollution affect it? Come up with a question to investigate. Then design an experiment to answer your question, and carry out your experiment. Organize your experiment to test only one variable, or one item being changed. Write down the steps so that another group could complete the experiment by following your instructions.

Remember to follow the steps of the scientific process.

91EXTEND

-Review Summaries and quizzes online @ www.macmillanmh.com

CHAPTER 1 Review

Microscopic producers, consumers, and decomposers are parts of the food chain.(pp. 54–63)

An ecosystem consists of the living and nonliving things in an area that interact with each other.(pp. 24–37)

Photosynthesis is the process of making food by using sunlight.(pp. 40–51)

Water, carbon, and nitrogen cycle through the living and nonliving parts of the environment.(pp. 80–89)

Food chains, webs, and pyramids show how energy flows within an ecosystem.(pp. 66–77)

Fill each blank with the best term from the list.

abiotic factor, p. 27

energy

pyramid, p. 76

eukaryote, p. 58

niche, p. 36

nitrogen cycle, p. 86

omnivore, p. 73

transpiration, p. 48

water cycle, p. 83

1. Energy from sunlight is a(n). 6 LS 5.e

2. Everything an organism does and everything it needs make up its

. 6 LS 5.e

3. A complex organism that has a nucleus in each cell would be classified as a(n) . 6 LS 5.b

4. A(n) would eat both producers and consumers. 6 LS 5.b, c

5. The term describes the loss of water from leaves. 6 LS 5.a

6. A model showing how energy moves through a food chain is a(n) . 6 LS 5.b

7. Evaporation, condensation, and precipitation are parts of the

. 6 LS 5.b

8. Denitrifying bacteria are an important part of the . 6 LS 5.b

Make aStudy Guide Take a sheet of paper and tape your lesson study guides as shown. Use the study guides to answer the questions on these pages.

Summarize the Main Ideas

92


Answer each of the following in complete sentences.

9. Cause and Effect What effect would over-logging of trees have on the amount of carbon dioxide in the atmosphere? 6 LS 5.a

10. Critical Thinking How does the angle at which the Sun’s rays strike Earth affect the number and typesof organisms found in different areas of the world? 6 LS 5.b, e

11. Predict What two effects might occur if most of the phytoplankton living in the world’s oceans were destroyed? 6 LS 5.a

12. Infer Explain why Earth is probably the only planet in our solar system that has soil. 6 LS 5.b

13. Explanatory Writing Be a teacher for the day. How would you explain the nitrogen cycle to your students? 6 LS 5.b

Save the TreesSuppose a kind of insect is destroying all the Joshua trees. Your goal is to convince state officials that funding must be made available to save the Joshua trees.

What to Do

1. Find out what niche the Joshua trees occupy. In what ways do other organisms living in the same ecosystem depend on these trees?

2. Prepare a display to show officials how the destruction of the Joshua trees could disrupt the food chains in the ecosystem.

Analyze Your Results

▶ Explain how a disruption in one part of an ecosystem can have far-reaching effects.

▶ Would the benefits of saving the Joshua tree outweigh the risks of spraying to prevent insect damage?

How do organisms exchange energy and nutrients in an ecosystem?

9393

1 What do microscopic organisms provide to larger organisms? 6 LS 5.b

A fresh water

B composing organisms

C increased sunlight

D food

2 Which of the following types of organisms turns energy from the Sun into chemical energy? 6 LS 5.a

A producers

B consumers

C decomposers

D composers

3 Look at the table below.

Category A Category B

tomato plant

fern

cyanobacteria

willow tree

grass

elephant

panther

humpback whale

field mouse

hawk

These organisms are grouped into 6 LS 5.c

A decomposers and tertiary

consumers.

B primary consumers and

scavengers.

C producers and consumers.

D omnivores and producers.

4 4 What is the role of a decomposer when plants die? 6 LS 5.b

A to eat the bacteria in the soil

B to store carbon for the plants

C to break down plant proteins

D to turn nitrates into nitrogen gas

5 5 Why are organisms such as earthworms and fungi called decomposers? 6 LS 5.c

A They break down very quickly

after they die.

B They break down other organisms

into simpler substances.

C They are the only organisms that

cannot make their own food.

D They break down carbon dioxide

into oxygen through respiration.

6 Which of the following best describes the role of roots and stems in a plant? 6 LS 5.a

A Roots and stems transport water

and minerals to the leaves so that

photosynthesis can occur.

B Roots and stems help the plant

move and keep cool in hot weather.

C Roots and stems transport water

and minerals to the flowers to

attract bees so that pollination

can occur.

D Roots and stems are where

photosynthesis takes place.

94

7 The diagram below shows an ocean energy pyramid.

Which organism in the energy pyramid is a secondary consumer? 6 LS 5.b

A seal

B penguin

C fish

D plant

8 8 What adaptations do plants have to live in desert environments? 6 LS 5.e

A They reflect light from the Sun.

B They migrate during the day to

cooler areas.

C They store water in spongy tissues.

D They do not grow in desert

environments.

9 9 Microscopic organisms that recycle organic materials back into the food chain are 6 LS 5.b

A producers.

B decomposers.

C users.

D consumers.

100 The energy in a community flows from producer to primary consumer and from primary consumer to 6 LS 5.c

A tertiary consumer.

B decomposer.

C secondary consumer.

D top predator.

11 1 A scientist observes a crow eating both insects and grass. What can she conclude about crows? 6 IE 7.e

A Crows will never eat higher-level

consumers.

B The crow will always eat only

insects or grasses.

C The crow is the only organism

that eats insects and grasses.

D Crows will eat both insects

and grasses.

12 2 Some populations occupy niches of such importance that many other organisms depend on them. These populations are called keystone species. Which of the following is an example of a keystone species? 6 LS 5.e

A Venus’s-flytraps catching flies

in the garden

B moles digging in the soil, creating

long tunnels under grass

C beavers building a dam, creating

a valuable wetland

D birds building a nest high up

in a tree

Materials prepared by PASS at 95

Chapter 1: Earth's Ecosystems

Documents

Transcript of Chapter 1: Earth's Ecosystems