• Quick retrieval from earlier learning (Osmosis and percentage change in mass). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. A potato cylinder had a mass of 4 g. After 30 minutes in a sugar solution its mass was 3.4 g. What is the percentage change in mass? (Use a minus sign for a loss.) → -15 %Prompt: percentage change = (final − initial) ÷ initial × 100
2. Potato pieces were left in sugar solutions. Percentage change in mass: 0 mol/dm³: +15 % 0.2 mol/dm³: +5 % 0.4 mol/dm³: −5 % 0.6 mol/dm³: −15 % 0.8 mol/dm³: −25 % Between which concentrations is the solution that matches the concentration inside the potato cells? (0–0.2 mol/dm³ / 0.2–0.4 mol/dm³ / 0.4–0.6 mol/dm³ / 0.6–0.8 mol/dm³) → 0.2–0.4 mol/dm³Prompt: Where there is no net movement of water, the mass does not change.
3. Why does a plant cell in pure water not burst? (Chloroplasts absorb the water / Its vacuole pumps water out / Its strong cell wall stops it expanding too far, so it becomes turgid / It cannot take in water) → Its strong cell wall stops it expanding too far, so it becomes turgidPrompt: Which structure do plant cells have that animal cells lack?

• Show a microscope image of cells and ask what students think they are looking at.
• Share the objective: Diffusion, osmosis or active transport?. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Which process is this: urea passing from cells into the blood?
• Step 1: Diffusion: particles move down a concentration gradient with no energy needed.
• Step 2: So the answer is: diffusion
• Answer: diffusion
• 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. Which process is this: water entering root hair cells from moist soil? (diffusion / osmosis / active transport) → osmosisPrompt: Is it water specifically? Is it going against the gradient?
2. Root hair cells contain many mitochondria. What does this suggest? (They photosynthesise / They do not respire / They absorb water only by diffusion / They use active transport, which needs energy) → They use active transport, which needs energyPrompt: What do mitochondria provide?

• 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. Which process is this: glucose absorbed from the gut when its level there is low? (diffusion / osmosis / active transport) → active transportPrompt: Is it water specifically? Is it going against the gradient?
2. Transport in cells: which statement is true? (Active transport only happens in plants. / Water moves by osmosis from a concentrated to a dilute solution. / Osmosis needs energy from respiration. / Osmosis is the movement of water molecules.) → Osmosis is the movement of water molecules.Prompt: Which process needs energy?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-8.