• Quick retrieval from earlier learning (Digestive enzymes and the molecules they make). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Which enzyme is described here: breaks proteins down into amino acids? (amylase (a carbohydrase) / protease / lipase) → proteasePrompt: The enzyme's name often sounds like the food it breaks down.
2. Amylase was mixed with starch at different temperatures. Iodine was used to time how long the starch took to disappear: 20 °C: 9 min 30 °C: 4 min 40 °C: 7 min 50 °C: 10 min 60 °C: starch still present after 20 min At which temperature did amylase work fastest, in °C? → 30 °CPrompt: Fastest means the shortest time.
3. A piece of bread tastes sweeter after you chew it for a long time. Why? (The bread gets warmer / Amylase in saliva breaks starch into sugar / Saliva contains lipase that makes sugar / Chewing adds sugar) → Amylase in saliva breaks starch into sugarPrompt: What enzyme is in your mouth?

• Show a microscope image of cells and ask what students think they are looking at.
• Share the objective: How enzymes work: active sites, temperature and pH. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Why does a reaction speed up as temperature rises towards the optimum?
• Step 1: More kinetic energy means more successful collisions between enzyme and substrate.
• Step 2: So the answer is: Molecules move faster, so enzyme and substrate collide more often
• Answer: Molecules move faster, so enzyme and substrate collide more often
• 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. What happens to an enzyme above its optimum temperature? (It works faster and faster forever / It is killed like a cell / It turns into a different enzyme / Its active site changes shape and it is denatured) → Its active site changes shape and it is denaturedPrompt: Enzymes are proteins; heat breaks the bonds holding their shape.
2. Enzymes: which statement is NOT true? (Enzymes are biological catalysts. / Most human enzymes work best at about 37 °C. / All enzymes work best at pH 7. / Enzymes are proteins.) → All enzymes work best at pH 7.Prompt: Is the effect of cold permanent?

• 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. Enzymes: which statement is NOT true? (Enzymes are biological catalysts. / Enzymes are not used up in the reactions they speed up. / Enzymes are proteins. / Cold temperatures denature enzymes permanently.) → Cold temperatures denature enzymes permanently.Prompt: Is the effect of cold permanent?
2. Pepsin works best at pH 2. Where in the body does it work? (the small intestine / the mouth / the blood / the stomach) → the stomachPrompt: Which part of the gut is very acidic?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.