• Quick retrieval from earlier learning (Decomposers and recycling nutrients; The carbon cycle). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Compost heaps rot faster when they are… (warm, moist and have air / completely dry / frozen / sealed in plastic with no air) → warm, moist and have airPrompt: Microorganisms need suitable conditions to grow.
2. Does this process remove carbon dioxide from the air or add it: burning forests? (removes CO₂ from the air / adds CO₂ to the air) → adds CO₂ to the airPrompt: Which process do green plants use to make glucose?
3. Is a mushroom a producer, a consumer or a decomposer? (producer / consumer / decomposer) → decomposerPrompt: Does it make food, eat living things, or break down dead things?

• Show a food web and ask what would happen if one animal disappeared.
• Share the objective: Decomposers, decay rates and recycling nutrients. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A bag of grass clippings had a mass of 200 g. After 10 days in a compost bin its mass was 180 g. What was the mean rate of decay, in g per day?
• Step 1: 200 − 180 = 20 g
• Step 2: 20 ÷ 10 = 2
• Step 3: So the answer is: 2
• Answer: 2
• 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. A bag of grass clippings had a mass of 120 g. After 8 days in a compost bin its mass was 108 g. What was the mean rate of decay, in g per day? → 1.5Prompt: Find the mass lost.
2. Why do gardeners turn their compost heaps regularly? (to kill all the microorganisms / to dry it out completely / to add oxygen for the decomposers' aerobic respiration / to cool the heap to 0 °C) → to add oxygen for the decomposers' aerobic respirationPrompt: Decomposers are living organisms that respire.

• 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 biogas generator lets waste decay without oxygen. What useful gas does it produce? (nitrogen / helium / methane, which can be burned as a fuel / oxygen) → methane, which can be burned as a fuelPrompt: This gas is also the main part of natural gas.
2. Decay: which statement is NOT true? (Decay returns mineral ions to the soil. / Decomposers need no oxygen at all. / Decay is faster when it is warm and moist. / Compost can be used as a natural fertiliser.) → Decomposers need no oxygen at all.Prompt: Does freezing speed decay up or slow it down?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-10.