• Quick retrieval from earlier learning (Food webs and interdependence). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Pond food web: algae are eaten by tadpoles and water fleas. Tadpoles and water fleas are eaten by small fish. Small fish are eaten by herons. If the small fish died, what would happen to the herons? (They would increase / They would eat algae / They would decrease or move away / Nothing) → They would decrease or move awayPrompt: What do herons eat in this web?
2. Why is a food web more realistic than a single food chain? (Food webs only show plants / Animals only ever eat one food / Food webs have no producers / Most animals eat, and are eaten by, more than one kind of living thing) → Most animals eat, and are eaten by, more than one kind of living thingPrompt: Does a fox eat only rabbits?
3. Food webs: which statement is NOT true? (A food web contains only one food chain. / Predator and prey populations often rise and fall in cycles. / Animals often compete for food, water and space. / Plants compete for light, water and minerals.) → A food web contains only one food chain.Prompt: Think about what happens when one population changes.

• Show a food web and ask what would happen if one animal disappeared.
• Share the objective: Energy transfer and pyramids. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Producers in a field capture 20000 kJ of energy. About 10% of the energy passes to each next level. How much energy reaches the tertiary consumers, in kJ?
• Step 1: 20000 ÷ 1000 = 20
• Step 2: So the answer is: 20 kJ
• Answer: 20 kJ
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. Producers in a field capture 10000 kJ of energy. About 10% of the energy passes to each next level. How much energy reaches the primary consumers, in kJ? → 1000 kJPrompt: 10% means divide by 10 at each step.
2. A level of a food chain contains 8000 kJ. The next level gets 1600 kJ. What is the percentage efficiency of the energy transfer? → 20 %Prompt: efficiency = energy passed on ÷ energy available × 100

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. A level of a food chain contains 10000 kJ. The next level gets 1500 kJ. What is the percentage efficiency of the energy transfer? → 15 %Prompt: efficiency = energy passed on ÷ energy available × 100
2. Why is only about 10% of energy passed to the next level of a food chain? (Plants keep all the energy / Energy is destroyed at each level / Animals refuse to eat most of their food / Much is used for respiration and movement, or lost as heat and waste) → Much is used for respiration and movement, or lost as heat and wastePrompt: Energy is never destroyed. Where does it go instead?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-7.