Teachers TryScience

Procedure

1. Begin the lesson by having a thought-provoking question on the board as students come in. For example, you could ask, “Why does an owl need the sun to survive? Give as many reasons as you can think of.” Direct students to answer the question individually in their notebooks. While they are working, circulate to see what they have written. If a student writes something like, “for warmth,” reinforce that the answer is correct, but press the student for more reasons that the sun is important to all organisms. If necessary, give a hint like, “Think about where the owl gets its food/energy from.” After a few minutes, allow the students to discuss their answers with a partner or small group. Then conduct a whole class discussion about why the sun is necessary for life. Include all reasonable responses in a list on the board such as “for warmth, to see, to get energy through the food web, etc.” Tell the students that today we will be focusing on the idea of how energy flows from the sun through a food web.
2. As an alternative, you could begin the class by giving four students pictures of ecosystem roles such as, sun, grass, mouse, and owl. Have these four students come to the front of the classroom and ask the class to arrange them in a logical order. After ordering the roles, have the students explain why they chose that order.

3. Continue the whole class discussion by asking students to explain how the owl gets energy from the sun through the food web. (If students do not have adequate background knowledge of photosynthesis, you will need to stop a do a mini lesson of that here.) Someone might say, “Well, the owl eats a mouse who ate some grass, which got energy from the sun through photosynthesis.” Draw a picture of the food chain described on the board. Put the sun at the bottom and the organisms getting energy stacked on top (see below). Include arrows showing the flow of energy. Be sure that the arrows go to the organism who is getting the energy.
   
   Owl

Mouse

Grass

SUN

4. Tell the students that what you have drawn is a food chain. Ask the students if the owl only eats mice or if the mice only eat grass. They should explain that the ecosystem is probably more complicated. Add other organisms to your drawing making sure to connect with arrows going from the prey organism to the predator organism. Tell the students that the new "messier" version is called a food web. Tell the students that they will be making food webs for another ecosystem.
5. Before introducing the ecosystems that they will be using to create a food web, review the ecosystem roles of organisms at different trophic levels including producers, primary consumers, secondary consumers, tertiary consumers (usually top predators), and decomposers.
6. Have the students work with their groups to come up with examples of organisms from each trophic level. Circulate to all the groups making sure that students can explain why each example fits into the stated trophic level.
7. Once you are sure the students are comfortable with the vocabulary, introduce the organism cards (or other resource) that they will be using to create a food web. Tell the students that they need to create a rough draft of the food web in this ecosystem using at least eight to ten organisms. They need to include the sun as well as at least one organism from each trophic level. Pass out the organism information and scratch paper for the students to create their food webs. If you are using organism cards, students may want to organize the cards into the food web shape before writing it down. Once the students start writing, make sure that they are showing the flow of energy with their arrows from the sun to the producers, from the producers to the primary consumers, from the primary consumers to the secondary consumers, etc.
8. Once the groups of students have developed a rough draft of their food web on paper, stop them and introduce the fact that they will be turning this food web into a mobile. Before explaining the materials for the mobiles, tell the students that making the mobile will be a challenging experience and that they need to use engineering design principles to help them succeed. Review (or introduce) the engineering design flow chart from PBSkids. Remind students that they should come up with a plan for creating their mobile, then put the plan into action. As they are working, they should feel free to tweak their plan or make changes as necessary in order to make the plan function better, just as an engineer would when designing a product.
9. When the students feel comfortable with the concepts in the engineering design process, introduce the materials that they may use for the mobiles. Explain that they will need to create a card for the sun and for each organism in their food web. Then they will need to find a way to hang the cards so that the mobile balances and the feeding relationships in the food web are properly represented.
   1. If the students need specific direction, they can create a basic mobile using a coat hanger and string. Show the students that they can use different lengths of string to hang the cards at different heights to represent the trophic levels. They will need to be aware of balance as they place the strings on the coat hanger.
   2. If students are more advanced, they can use another mobile design such as one of the types discussed in the background information. Be sure to remind these students that they need to be aware of balance when creating their mobiles and that they can vary the size or weight of the card, the length of the wire, or the balance point in order to achieve balance.
10. At this point you can introduce the rubric that will be used to grade the projects. Using the rubric, remind the students that their mobile needs to balance but ALSO needs to show the feeding relationships correctly. Also remind students that aesthetic concerns are part of the engineering process (part of the reason we all love Apple products is because they look beautiful!). Therefore, they need to try to make the mobile as aesthetically pleasing as possible.
11. Once students understand the task, allow them to gather the materials that they think they will need. As the students are working, circulate among the groups helping them to think through design challenges as they arise and providing appropriately scaffolded support as necessary. Continue to reinforce the requirements of the rubric with each group to be sure that they are meeting the task.
12. Once the students have completed their mobiles, allow the groups to present their work to the class. Instruct the students to explain the science content in their mobile as well as any engineering design challenges that they met and overcame in the development process. Encouraging students to think aloud about how they worked on a problem improves their meta-cognition.
13. Tell each group to use the rubric to grade their own work. Then show the groups what grade you have given them and discuss any differences in the grading by discussing elements of the rubric.