Food Webs BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN. SC.F The student knows how all animals depend on plants.

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1 activity 39 Food Webs BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN Grade 3 Quarter 4 Activity 39 SC.B The student knows how to trace the flow of energy in a system (e.g., as in an ecosystem). SC.B The student knows that some source of energy is needed for organisms to stay alive and grow. SC.F The student knows how all animals depend on plants. SC.G The student knows ways that plants, animals, and protists interact. SC.G The student knows that living things compete in a climatic region with other living things and that structural adaptations make them fit for an environment. SC.H The student knows that to work collaboratively, all team members should be free to reach, explain, and justify their own individual conclusions. SC.H The student knows that a model of something is different from the real thing but can be used to learn something about the real thing. ACTIVITY ASSESSMENT OPPORTUNITIES The following suggestions are intended to help identify major concepts covered in the activity that may need extra reinforcement. The goal is to provide opportunities to assess student progress without creating the need for a separate, formal assessment session (or activity) for each of the 40 hands-on activities at this grade level. 1. Ask, How does food energy flow in a food chain? (The food energy flows in one direction, from a producer to a consumer that eats producers to a consumer that eats other consumers.) How does food energy flow in a food web? (Food energy still flows from producer to different levels of consumers, but it flows in many different directions.) broward county hands-on science Quarter 4 403

2 2. Use the Activity Sheet(s) to assess student understanding of the major concepts in the activity. In addition to the above assessment suggestions, the questions in bold and tasks that students perform throughout the activity provide opportunities to identify areas that may require additional review before proceeding further with the activity. 404 activity 39 Food Webs

3 activity 39 Food Webs OBJECTIVES A vast food web connects all life in a community. The students create food webs that include the plants and animals they have discussed as well as other common animals. The students create diagrams of food webs on paper compare food chains to food webs infer why real food webs are so complex SCHEDULE About 40 minutes VOCABULARY food web MATERIALS For each team of two 1 Activity Sheet 39 1 set Food Web cards 1 piece paper, white, 11 in. 17 in.* 1 pair scissors* For the class 1 btl glue markers or crayons* paper, scrap* Delta Science Reader Food Chains and Webs *provided by the teacher PREPARATION Make a copy of Activity Sheet 39 for each team of two. Copy a set of Food Web cards for each team of two, using the heaviest stock paper your copy machine will accept. Squirt some glue onto a piece of scrap paper for each team of two. BACKGROUND INFORMATION Every living thing, whether plant or animal, must have food to live. Plants use the energy in sunlight to manufacture their own food from carbon dioxide and water, but animals must eat plants or other animals to survive. The simple progressions studied in these activities, such as grass cricket mouse owl, are called food chains. In most ecosystems, however, the arrangements are not this simple, and are better illustrated as food webs that show many organisms and interconnected food chains. owl mouse cricket Figure A food web. grass anole seeds fox The simple food web shown in Figure 39-1 illustrates the greater complexity of a food web as compared to a food chain. In this web, there are two producers (grass and seeds), three primary consumers (cricket, mouse, and broward county hands-on science Quarter 4 405

4 fox), four secondary consumers (mouse, fox, anole, and owl), and two tertiary consumers (fox and owl). Nearly all the consumers depend on more than one type of prey for food. Activity Sheet 39 Food Webs leaves fruit seeds cricket fox flowers butterfly robin mouse anole earthworm owl 1 Guiding the Activity Write grass mouse owl on the board, and ask, What do we call this sequence? Add cricket and anole, as shown in Figure Additional Information This is a food chain. grass mouse owl cricket anole Ask, How should we connect these two additional animals to this food chain? Remind students that sometimes owls eat anoles, and mice eat crickets, and ask, How can we add arrows to show this? Ask, How is this diagram different from a simple food chain? 406 activity 39 Food Webs Figure Building a simple food web. The grass should have an arrow pointing to the cricket and the cricket should have an arrow pointing to the anole. Students should suggest adding an arrow pointing from the anole to the owl, and an arrow pointing from the cricket to the mouse, as shown in Figure This is a more complex arrangement. Consumers eat more than one type of prey, and prey are eaten by more than one type of consumer.

5 2 3 Guiding the Activity Write food web on the board. Explain that in most places, plants and animals are connected in more complicated ways ways that resemble webs more than chains. This complex arrangement of organisms and food chains is called a food web (see Figure 39-3). Distribute a copy of Activity Sheet 39, an 11-in. 17-in. piece of paper, scissors, markers, a scrap of paper with glue, and a set of Food Web cards to each team of two. Instruct students to cut the circles out of Activity Sheet 39 and glue them randomly onto the large piece of paper. They also should cut apart the Food Web cards and stack them. The students should use the information on the Food Web cards to draw arrows showing all the connections between the plants and animals on their piece of paper (see Figure 39-4). Demonstrate this by having all the teams read the fox card along with you, and draw an arrow for each of the connections mentioned. Additional Information grass mouse owl cricket anole Figure Building a simple food web. Tell students to spread the circles out on the paper so that there is a lot of room between them. There should be arrows pointing to the fox from the fruit, robin, mouse, cricket, butterfly, seeds, anole, and leaves. Allow the students time to go through the Food Web cards and complete their charts. fruit owl earthworm mouse seeds leaves cricket fox robin flowers butterfly anole Figure Initial connections in the students food web. broward county hands-on science Quarter 4 407

6 4 5 Guiding the Activity Ask, Does your chart look more like a food chain or a food web? Tell students that most relationships between living things are more like food webs than food chains. Conclude by asking, Do animals eat only one kind of prey? Are they eaten by only one kind of predator? Why do you think that food webs, rather than chains, exist in nature? As appropriate, read or review pages 4 9 of the Delta Science Reader Food Chains and Webs. Additional Information The chart looks like a food web. Many food webs are so complex that it is difficult to diagram them accurately. From their diagrams, students should see that most animals eat a variety of plants or other animals for food. Lead them to realize that, in nature, animals encounter a number of other organisms daily and that it would be to their advantage to be able to draw nourishment from a variety of these organisms. If they depended exclusively on one prey item, as the food-chain arrangement implies, they could starve to death if that prey item were suddenly to disappear. R EINFORCEMENT Have students create food webs with common animals from your region. Be sure that they include plants, several plant-eating animals, and at least one predator. Challenge them to include humans in their food web. Assessment Opportunity This Reinforcement also may be used as an ongoing assessment of students understanding of science concepts and skills. SCIENCE JOURNALS Have students place their completed activity sheets in their science journals. 408 activity 39 Food Webs C LEANUP Display the food web diagrams in the classroom. Students may want to save the Food Web cards for additional activities as described in Connections. Return the bottle of glue to the kit. SCIENCE AT HOME Have students look in their refrigerators and cupboards to research the food webs of which they are part. They may want to draw a diagram of these and bring them to class to discuss.

7 Connections Science Extension Explain that when a plant uses the energy in sunlight to make its own food, most of that energy is used for the plant s life processes. Only about 10% of the energy that a plant receives from sunlight is stored in the plant. When a mouse eats the plant, it uses most of the food energy it takes in for its own life processes and stores only about 10% in its body. When an owl eats the mouse, the owl gets only about 10% of the food energy that the mouse took in. Draw a large pyramid on the board, and divide it into three sections. Beginning at the bottom, label the sections grass, mice, and owl. Tell students that the pyramid shows what happens as food energy passes from producers to different levels of consumers in a food chain. To show students how quickly energy is lost in a food chain, draw a second pyramid the same size as before but with an additional section labeled snakes between the mice and the owl. The sections for the grass and mice should be kept the same size as they were in the first pyramid. Now, draw a third pyramid with yet another section labeled crickets between the grass and the mice. In this third pyramid, keep the section for grass the same size as before, but reduce the sizes of the mice, snake, and owl sections to accommodate the crickets section. Explain that because such a small amount of the food energy stored in plants ever reaches the top consumer in a food chain, most chains contain no more than four levels of consumers. Science and Math Divide the class into teams of three. Give one student in each team a sheet of graph paper, and tell the student that he or she represents a plant. Have the student outline a block of squares on the graph paper and cut it out. Then tell the student to cut off a row of 10 squares from the block and pass it to a second student, who represents a mouse. Tell the mouse to cut off one square from the row and pass it to the third student, who represents an owl. Students can see that only a small portion of the original food energy stored in the plant reaches the owl. You may want to have students repeat the activity to illustrate a fourlevel chain that includes a snake and a fivelevel chain that includes a cricket. (Students will need to tape sheets of graph paper together in order to start with a block large enough for the owl to receive one square.) Science, Technology, and Society Explain that just as food energy passes up a food chain, so do many poisonous substances. However, because these poisons are not used for life processes, all of the poison that an animal takes in is passed on to the next-level consumer. If a farmer s field is sprayed with a poison to kill insect pests, mice that eat the dead and dying insects will take in the poison, too. An owl, hawk, or fox that eats the mice will take in the poison. In this way, poisons work their way up a food chain and harm or kill animals that were not meant to be poisoned. Ask students to find out more about poisons in food chains. broward county hands-on science Quarter 4 409

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