CHAPTER 20 Matter and Energy in the Environment Energy in Ecosystems What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you ve read this lesson, reread the statements to see if you have changed your mind. Before Statement After LESSON 3 Key Concepts How does energy move in ecosystems? How is the movement of energy in an ecosystem modeled? 5. The Sun is the source for all energy used by living things on Earth. 6. All living things get their energy from eating other living things. How does energy move in ecosystems? Think of an ecosystem. That ecosystem might seem peaceful. If you visit, though, you will notice that it is full of movement. Birds squawk and beat their wings. Plants sway in the breeze. Insects buzz. Animals run over leaves. An organism requires energy to move. Growth, reproduction, and other life functions require energy. Most of the energy for life on Earth comes from the Sun. Energy does not cycle through ecosystems like matter does. Energy flows in one direction. In most cases, energy flow starts with the Sun. It moves from one organism to another organism. Many organisms get energy by eating other organisms. Organisms can change energy into different forms of energy. Not all the energy an organism gets is used for life processes. Some is released into the environment as thermal energy. Energy cannot be created or destroyed. Its form can change, though. This idea is called the law of conservation of energy. Identify Important Words As you read this lesson, highlight all the words you do not understand. Then underline the part of the text that can help you learn what those words mean. Key Concept Check 1. Explain How do the movements of matter and energy differ? Reading Essentials Matter and Energy in the Environment 343
Producers Producers make things. Living things that make their own food from materials in their environments are called producers. Most of these producers use the process of photosynthesis (foh toh SIHN thuh sus). Some use the process of chemosynthesis (kee moh SIHN thuh sus). Photosynthesis Plants, algae, and some bacteria use photosynthesis to make their food, as shown below. Photosynthesis is a series of chemical reactions that convert light energy, water, and carbon dioxide into the food energy molecule glucose and give off oxygen. This process is part of the carbon cycle that you read about earlier in this chapter. 2. Identify What food do producers make in photosynthesis? Light energy Sugars Carbon dioxide Water Photosynthesis Reading Check 3. Explain During chemosynthesis, what do producers use to make food? 4. Classify To which group of consumers do most humans belong? Chemosynthesis Some producers use chemosynthesis to make food. Chemosynthesis is the process during which producers use chemical energy in matter rather than light energy and make food. Chemosynthesis can occur on the deep ocean floor. Hydrothermal vents are outlets for compounds that contain hydrogen and sulfur, as well as thermal energy from inside Earth. Chemosynthetic bacteria that live there use the chemical energy in the compounds and produce food. Consumers Consumers do not make their own energy-rich food. They get their energy by consuming, or eating, other organisms. Consumers can be classified by the type of food that they eat. The groups of consumers include herbivores, carnivores, omnivores, and detritivores. Herbivores, Carnivores, and Omnivores Herbivores eat only producers. A deer eats only plants, so it is an herbivore. Carnivores eat other animals. Lions and wolves are carnivores. Omnivores eat both producers and other consumers. A bird that eats berries and insects is an omnivore. 344 Matter and Energy in the Environment Reading Essentials
Detritivores Detritivores (dih TRI tuh vorz) get their energy by eating the remains of other organisms. Some detritivores, such as insects, eat dead organisms. Detritivores, such as bacteria and mushrooms, feed on and help decompose dead organisms. They are often called decomposers. They produce carbon dioxide that enters the air. Some decayed matter enters the soil. In this way, detritivores help recycle nutrients through ecosystems. They also keep dead organisms from piling up in ecosystems. Modeling Energy in Ecosystems You learned that energy does not cycle through ecosystems. Instead, energy flows through ecosystems. As it flows, organisms might use some energy for life processes. Energy might also be stored in the bodies of organisms as chemical energy. When consumers eat these organisms, the chemical energy moves into the bodies of the consumers. Such a transfer of energy can be from a producer to a consumer. It can also be from one consumer to another consumer. With each transfer of energy, some energy changes to thermal energy. Any extra thermal energy enters the environment from the bodies of consumers. Scientists use models to study this flow of energy through an ecosystem. The model they use depends on how many organisms they are studying. Food Chains A food chain is a model that shows how energy flows in an ecosystem through feeding relationships. In a food chain, arrows show the transfer of energy. A food chain is shown below. 3 2 1 The Sun emits energy. Plants make energy-rich food using sunlight. The mouse obtains energy by eating the plant. 5 The hawk obtains energy by eating the snake. 4 The snake obtains energy by eating the mouse. Use each side of your pyramid book to organize information about one of the ways energy flows in an ecosystem. Food Chain Food Web Key Concept Check 5. Explain How does a food chain model energy flow? 6. Identify Circle each producer and draw a square around each consumer in the food chain. Reading Essentials Matter and Energy in the Environment 345
Key Concept Check 7. Name two models used to show the transfer of energy in an ecosystem. Food Webs Imagine that you are working on a jigsaw puzzle of a prairie. The food chain is just one piece of that puzzle. It shows just one small part of the prairie. A food chain is like one piece of an ecosystem jigsaw puzzle. It can help you study parts of an ecosystem. It does not show the whole picture, though. Look again at the food chain. The mouse might also eat the seeds of other producers, such as corn or trees. The snake might eat other animals, such as frogs, crickets, or earthworms. The hawk might also eat other animals, such as mice, squirrels, rabbits, or fish. The feeding relationships in this ecosystem are complex. Scientists use a food web to study these feeding relationships. A food web is a model of energy transfer that shows how food chains in a community are interconnected. A food web is many overlapping food chains. The food web below shows the complex feeding patterns in an ecosystem. Arrows show how energy flows. Orca Great white shark 8. Interpret Diagrams Draw a circle around the organism in the food web that receives energy from the greatest amount of producers and consumers. Squid Copepods Diatoms Leopard seal Krill Fish 346 Matter and Energy in the Environment Reading Essentials
Energy Pyramids Food chains and food webs show how energy moves in an ecosystem. They do not show how the amount of energy in an ecosystem changes, though. An energy pyramid is a model that scientists use to show the amount of energy available in each step of a food chain. The steps of an energy pyramid are called trophic (TROH fihk) levels. Look at the energy pyramid below. Producers, such as plants, make up the bottom trophic level. Consumers, such as squirrels, that eat producers make up the next level. Consumers, such as hawks, that eat other consumers, make up the highest level. Notice that as you move to a higher level, there is less energy available for consumers. Why? As you read earlier, organisms use some of the energy they get from food for life processes. During life processes, some energy is changed to thermal energy. The thermal energy is then transferred to the environment. Available energy decreases. Trophic level 3 (1 percent of energy available) Trophic level 2 (10 percent of energy available) Trophic level 1 (100 percent of energy available) Math Skills The first trophic level producers obtains energy from the Sun. They use 90 percent of the energy for their own life processes. Only 10 percent of the energy remains for the second trophic level herbivores. Assume that each trophic level uses 90 percent of the energy it receives. Use the following steps to calculate how much energy remains for the next trophic level. First trophic level gets 100 units of energy. First trophic level uses 90 percent = 90 units Energy remaining for second trophic level = 10 units Second trophic level uses 90 percent = 9 units Energy remaining for third trophic level = 1 unit 9. Use Percentages If the first trophic level receives 10,000 units of energy from the Sun, how much energy is available for the second trophic level? 10. Interpret Diagrams How does the amount of available energy change at each trophic level? Reading Essentials Matter and Energy in the Environment 347
Mini Glossary chemosynthesis (kee moh SIHN thuh sus): the process during which producers use chemical energy in matter rather than light energy to make food energy pyramid: a model that scientists use to show the amount of energy available in each step of a food chain food chain: a model that shows how energy flows in an ecosystem through feeding relationships food web: a model of energy transfer that scientists use to show how food chains in a community are interconnected photosynthesis (foh toh SIHN thuh sus): a series of chemical reactions that convert light energy, water, and carbon dioxide into the food energy molecule glucose and give off oxygen 1. Review the terms and their definitions in the Mini Glossary. Write a sentence that describes one way in which photosynthesis and chemosynthesis differ. 2. Fill in the graphic organizer below. Name and describe the three models that scientists use to show the flow of energy through an ecosystem. Clues have been provided. Food Chain What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind? complex feeding relationships in an ecosystem ConnectED Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson s resources. END OF LESSON 348 Matter and Energy in the Environment Reading Essentials