Explain that the class is going to make a large food chain. Ask: Where does the energy come from to start the food chain? (The sun) Explain that while the energy for living things comes from the sun, there are many other factors that living things depend on to stay alive. Ask: Where does soil come from? (Broken down rocks and decomposed organic material) Without decomposers to help break down dead trees and animals, there would be no organic material in soil. Without organic material, plants would not be able to grow.
Explain that the living environment is really a giant interconnected web of life. Have students move to an open area and sit in a large circle. Pass out the index cards labeled with the things found in the environment. Each student (or pair of students if it's a large class) should get one card. Explain that the card represents something that you can find in the natural world. Give the end of the ball of yarn to the student who is holding the card labeled "sun". Explain that because all energy we have here on Earth comes from the sun, this will be where the web starts. Have the "sun" hold the end of the string and pass the ball while unrolling it to the student that has the card labeled "grass." Explain that the grass uses sunlight to grow so it's connected to the sun. Ask: What else does the grass need to grow? (soil) Have the "grass" hold the string and pass the ball while unrolling the string to the student who is holding the card labeled "soil." Continue passing the ball of string around, having the students construct a model of a food web. Eventually, the class will be left with a giant tangled web. (The students can untangle it by dropping their string and rolling the yarn back into a ball.)
Explain that most people don't even think about all the connections that go into the simple things that make our lives possible here on Earth.
Divide the class into groups of three or four students and give the groups the materials needed to complete the activity on the "Food for Life" lab sheet. The materials needed are pencil, tape, and 6 strips of paper (6x1 inch).
Below are the directions from the "Food for Life" lab sheet.
1. Write the word "tuna" on one of the strips of paper. Using tape, tape the two ends of the strip together so that you have a ring with the word on the outside. Tuna are predators. What does that mean?
2. Tuna eat smaller fish, like mackerel and herring. Write the name of one of these fish on a second piece of paper. Pass the end of the second strip through the opening in the "tuna" ring and bend it around to make a second ring. Tape it to secure the ring so that you have two rings connected. Mackerel and herring are also predators but they eat small animals like shrimp. Shrimp eat even smaller animals called zooplankton. Write "shrimp" and "zooplankton" on two other paper strips and link them to the chain. Which ring will you hook the zooplankton to? Why?
3. Zooplankton feed off of tiny phytoplankton called algae. Write the word "algae" on a strip. Which ring will you connect it to? Why?
4. The word phyto- means "plant." Where do algae get their energy from? What are you going to write on the last strip of paper? (sun)
5. Since people eat tuna, mackerel, herring, and shrimp, where would you link a ring that says "humans" on this chain?
6. Suppose that a fleet of fishing boats came into the area where tuna live and scooped up all the shrimp. Would that have any effect on the tuna? Explain your answer.
Lead a class discussion for each question. Make sure the students are making a connection that energy in animals' food is used to sustain life and that all food chains start with the sun's energy.
Have the students write a reflection in their Science journal for this scenario:
Suppose that there was a toxic spill that killed all the algae in the area. What members of the food chain would be affected? Why?