• 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 all the small fish died, what would probably happen to the tadpoles at first? (They would stay exactly the same / They would turn into fish / They would decrease / They would increase) → They would increasePrompt: What eats tadpoles?
2. What does "interdependence" mean in an ecosystem? (Every animal lives alone / Plants do not need animals at all / Only predators matter / Living things depend on each other, so a change to one affects others) → Living things depend on each other, so a change to one affects othersPrompt: Think of bees and flowers.
3. Food webs: which statement is NOT true? (A food web contains only one food chain. / Plants compete for light, water and minerals. / Removing one species can affect many others in a food web. / Predator and prey populations often rise and fall in cycles.) → 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 100000 kJ of energy. About 10% of the energy passes to each next level. How much energy reaches the primary consumers, in kJ? → 10000 kJPrompt: 10% means divide by 10 at each step.
2. A level of a food chain contains 4000 kJ. The next level gets 800 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 8 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 4000 kJ. The next level gets 800 kJ. What is the percentage efficiency of the energy transfer? → 20 %Prompt: efficiency = energy passed on ÷ energy available × 100
2. Why do food chains rarely have more than four or five levels? (There are not enough names for them / Top predators do not need energy / Plants stop growing / There is too little energy left to support more levels) → There is too little energy left to support more levelsPrompt: Think about how much is left after several 10% steps.

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