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2 Photo/Illustration Credits: Cover: Photodisc Collection/Getty; p. 2: Kenneth Murray/Photo Researchers, Inc.; p. 3: John Kaprielian/Photo Researchers, Inc.; p. 4: George Ranalli/Photo Researchers, Inc.; p. 5: George D. Lepp/ Photo Researchers, Inc.; p. 6: Nature s Images/Photo Researchers, Inc.; p. 7: Michael Fogden/Animals Animals/ Earth Scenes; p. 8: (bl) Paul & Joyce Berquist/Animals Animals/Earth Scenes; pp. 8 9 (c) Harcourt; p. 9 (tl) Premaphotos/Animals Animals/Earth Scenes; p. 10: Daybreak Imagery/Animals Animals/Earth Scenes; p. 11: Jonathan Massie/Wilkinson Studios, Inc.; p. 13: Jonathan Massie/Wilkinson Studios, Inc.; p. 14: photolibrary.com pty. ltd./index Stock Imagery; p. 15: Keith Levit/Index Stock Imagery. If you have received these materials as examination copies free of charge, Harcourt School Publishers retains title to the materials and they may not be resold. Resale of examination copies is strictly prohibited and is illegal. Possession of this publication in print format does not entitle users to convert this publication, or any portion of it, into electronic format.

3 Copyright by Harcourt, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Requests for permission to make copies of any part of the work should be addressed to School Permissions and Copyrights, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida Fax: HARCOURT and the Harcourt Logo are trademarks of Harcourt, Inc., registered in the United States of America and/or other jurisdictions. Printed in Mexico ISBN ISBN

4 From the trees in the forest to the houseplants in your home, plants are made up of three basic parts: roots, stems, and leaves. Each part has a special job to do to help a plant live and grow. What parts do roots and stems play? Most plant roots act as anchors. They keep a plant from falling over or blowing away in the wind. Roots also take in water and nutrients from the soil through tiny parts called root hairs. Water and nutrients are essential to a plant s survival. Stems support a plant and hold its leaves up so that they reach sunlight. Inside stems are tubes that carry water and nutrients from roots to leaves and flowers.

5 The main job of a plant s leaves is to make food. Leaves contain several layers of cells. The outer layer, called the epidermis, keeps the plant from drying out. The upper layer of the epidermis often has a layer of wax to help keep water in. The lower layer has structures called stomata. Stomata open during the day to take in carbon dioxide. Above the stomata is another layer of cells. These cells have air spaces between them. The air spaces contain water vapor and carbon dioxide ingredients necessary to make food.

6 Plants make food using water and nutrients from the soil, carbon dioxide from the air, and energy from sunlight. This foodmaking process, called photosynthesis, also produces oxygen. Oxygen is a by-product of photosynthesis. Plants do not need all the oxygen they produce, so they release the excess into the air. In a plant s leaves, cells contain organelles called chloroplasts. Chloroplasts contain chlorophyll, a green pigment, or coloring matter, that enables the plant to absorb and use light energy. Only cells with chloroplasts can make food.

7 Photosynthesis begins when chlorophyll absorbs energy from sunlight. The energy that is absorbed by chlorophyll helps water and carbon dioxide combine to form sugar. The sugar made by the plant is stored in the plant s leaves, stems, and sometimes even its roots. This is the food the plant needs to live and grow. After making food, the leaves of a plant release oxygen through the stomata. This release of oxygen into the air helps contribute to the world s supply of oxygen a gas you need to breathe. Plants also help by taking carbon dioxide, which you do not need, out of the air.

8 You ve learned that plants produce their own food. So they are called producers. Food provides energy for the plant allowing it to live and grow. Animals need energy to live and grow, too. Since animals can t make their own food, where does animal energy come from? Organisms that cannot make their own energy must eat to get the energy they need. When animals eat plants, the animals get the energy that is stored in those plants. The word consume means eat. Animals that eat plants or other animals are called consumers. You, a beetle, and a buffalo are all consumers. When you eat an apple, you take in the energy stored in the fruit. When a beetle eats leaves, and a buffalo eats grass, they are also taking in the energy stored in plants.

9 Even animals that eat other animals depend on plants. Without plants, beetles would not survive. Animals such as birds, that eat beetles would lose their food source, too. They also would not survive. All organisms need energy to live and grow. Almost all energy on Earth comes from the sun, directly or indirectly. Plants capture light energy from the sun and transform it into food energy. When consumers eat plants, they use the energy stored in food to carry out their life processes.

10 Plants are producers and the animals that eat plants or other animals are consumers. Producers and consumers live in ecosystems, which are communities of organisms and the environments in which they live. A desert ecosystem is shown here. In a desert ecosystem, there are plants such as cactus, sagebrush, and creosote bush. Some animals, such as kangaroo rats, depend on the plants for food. The food energy stored in the plant is transferred to the kangaroo rat. An animal that eats only plants is an herbivore. Herbivores are sometimes called first-level consumers.

11 Some animals do not eat plants. They get their energy by eating other animals. Snakes and foxes live in the desert, too. Snakes eat kangaroo rats. The energy that was stored in the kangaroo rat is transferred to the snake. An animal that eats other animals is called a carnivore. They are second-level consumers. Foxes eat snakes. The energy stored in the snake is transferred to the fox. This makes the fox a third-level consumer. When plants and animals die, the food energy left in their remains is consumed by decomposers. A decomposer is a consumer that gets its food energy by breaking down the remains of dead organisms. Decomposers include worms, fungi, and single-celled organisms such as bacteria and protists.

12 Each time something eats something else, energy is transferred from one organism to the other. The transfer of energy between organisms is called a food chain. At the beginning of every food chain are producers. Consumers make up all the other levels. First-level consumers eat producers. Second-level consumers eat first-level consumers. Third-level consumers eat second-level consumers, and so on. In this way, energy moves through each level of the food chain. All along the way, decomposers get energy from the remains of dead organisms. Unused nutrients are returned to the soil. Decomposers connect both ends of a food chain. In any single ecosystem, there are many different food chains. These food chains overlap. In a forest ecosystem, an owl might eat a mouse that eats seeds. The owl might also eat a snake that eats insects. The insects might have eaten grass. A food web shows the relationship between many different food chains in a single ecosystem. By studying food chains and food webs, it s easy to see that organisms depend on one another for survival. A change that affects one organism in the ecosystem can affect them all.

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14 In the food chains of most ecosystems, there are many more producers than there are consumers. Producers use about 90 percent of the energy they make during photosynthesis for their own life processes. Only 10 percent is stored in plant parts, such as roots, stems, leaves, fruits, and seeds. This means that first-level consumers get only 10 percent of the energy the producers made. These consumers then use 90 percent of that energy for their own life processes. They store the remaining 10 percent in their bodies. Most of the energy at any level of a food chain is used at that level. Only a small amount is actually passed on to the next level. An energy pyramid shows how much energy is available to pass from one level of a food chain to the next. Since only 10 percent of the energy at any level of the food chain is passed on to the next level, there is a great loss of energy at each level. Since less energy is available to organisms higher up the food chain, there are usually fewer organisms at these levels. There is simply not enough energy to support a large population.

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16 You re probably familiar with the cycle of the seasons or of water between Earth and the atmosphere. Did you know that cycles affect ecosystems? Most ecosystems are dependent on the water cycle to provide plants with the water they need. Another cycle that affects ecosystems is the nitrogen cycle. Nitrogen is a gas that makes up about 80 percent of Earth s atmosphere. It is important to all living things. However, before organisms can use nitrogen, its form must be changed. Sometimes nitrogen gas is changed into a usable form by lightning. Bacteria can also change nitrogen gas into a usable form. Nitrogen cycles through ecosystems via food chains. Nitrogen returns to the soil when organisms die and decompose. The exchange of carbon dioxide and oxygen between producers and consumers is also a cycle. Plants take in carbon dioxide and release oxygen. Humans and other animals take in oxygen and release carbon dioxide.

17 Producers use sunlight to make food energy. Consumers eat producers or other consumers to get energy. A food chain shows how the organisms in an ecosystem are connected to one another according to what they eat. Overlapping food chains form food webs. An energy pyramid shows how much food energy is passed from one organism to another in a food chain.

18 carnivore (KAHR nuh vawr) An animal that eats other animals; may be a second-level or third-level consumer (8) chlorophyll (KLAWR uh fihl) A green pigment that allows a plant to absorb the sun s light energy (4, 5) consumer (kuhn SOOM er) An animal that eats plants, other animals, or both (6, 7, 8, 9, 10, 12, 13, 14, 15) decomposer (dee kuhm POHZ er) A consumer that obtains food energy by breaking down the remains of dead plants and animals (9, 10) ecosystem (EE koh sis tuhm) A community of organisms and the environment in which they live (8, 10, 12, 14, 15) energy pyramid (EN er jee PIR uh mid) A diagram that shows how much food energy is passed from each level in a food chain to the next (13, 15) food chain (FOOD CHAYN) The transfer of food energy between organisms in an ecosystem (10, 12, 15) food web (FOOD WEB) A diagram that shows the relationships between different food chains in an ecosystem (10, 11, 15) herbivore (HER buh vawr) An animal that eats only plants (8) photosynthesis (foh toh SIHN thuh sis) The process in which plants make food by using water and nutrients from the soil, carbon dioxide from the air, and energy from sunlight (4, 5) producer (pruh DOOS er) A living thing, such as a plant, that makes its own food (6, 7, 8, 10, 11, 12, 15)

19 In most ecosystems, what kinds of organisms are producers? How are herbivores and carnivores alike? How are they different? What is a food web? What would happen if something changed in an ecosystem and there were suddenly more consumers than producers? Could this ecosystem last this way? Write a paragraph that explains the interdependence of organisms in an ecosystem. Work with a group of classmates to research an ecosystem near your community. Find out what living and nonliving things make up that ecosystem. Make a poster that illustrates how the organisms in the ecosystem interact. Which organisms are producers? Which are consumers? Share the reader with a family member. Together, use words, pictures, and arrows to diagram the events that must take place for you to have a glass of milk and a sandwich. What is the base of this food chain?

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