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Science lesson plan · 8th grade (Year 9 in England) · 30 minutes

Diffusion, osmosis or active transport?

Cells, genetics and evolution

CCSS NGSS.HS-LS1-2England: GCSE Combined Science: Cell biology

Objective and success criteria

Students will: Diffusion, osmosis or active transport?.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Osmosis and percentage change in mass

Leads to: Membrane structure, protein channels and bulk transport

Materials: Microscope images or slides, Cell diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • 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 3.2 g. After 30 minutes in a sugar solution its mass was 2.56 g. What is the percentage change in mass? (Use a minus sign for a loss.) → -20 %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? (Its vacuole pumps water out / Its strong cell wall stops it expanding too far, so it becomes turgid / It cannot take in water / Chloroplasts absorb the water) → Its strong cell wall stops it expanding too far, so it becomes turgidPrompt: Which structure do plant cells have that animal cells lack?

Hook · 3 min

  • 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.

I do: model it · 7 min

  • 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.

We do: guided practice · 6 min

  • 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: carbon dioxide entering a leaf? (diffusion / osmosis / active transport) → diffusionPrompt: Is it water specifically? Is it going against the gradient?
  2. What do diffusion and osmosis have in common? (Both are passive: they need no energy from respiration / Both move substances against a gradient / Both move only water / Both need mitochondria) → Both are passive: they need no energy from respirationPrompt: Osmosis is a special case of diffusion.

You do: independent practice · 7 min

  • 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.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Root hair cells contain many mitochondria. What does this suggest? (They do not respire / They use active transport, which needs energy / They absorb water only by diffusion / They photosynthesise) → They use active transport, which needs energyPrompt: What do mitochondria provide?
  2. Transport in cells: which statement is true? (Water moves by osmosis from a concentrated to a dilute solution. / Osmosis needs energy from respiration. / Active transport needs energy from respiration. / Active transport only happens in plants.) → Active transport needs energy from respiration.Prompt: Which process needs energy?

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Osmosis and percentage change in mass.
  • Use concrete materials: microscope images or slides.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Move on to: Membrane structure, protein channels and bulk transport.
  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

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

Free lesson plan from eurekami.com/lesson-plan-builder

eurekami

Diffusion, osmosis or active transport?

Name

Date

Score/ 6

  1. Question 1

    A poison stops respiration in root cells. Which process stops first?

    • A. diffusion of oxygen
    • B. all three equally
    • C. active transport of mineral ions
    • D. osmosis of water

  2. Question 2

    Which process is this: glucose absorbed from the gut when its level there is low?

    • A. diffusion
    • B. osmosis
    • C. active transport

  3. Question 3

    Transport in cells: which statement is true?

    • A. Water moves by osmosis from a concentrated to a dilute solution.
    • B. Active transport can move substances from a low to a high concentration.
    • C. Active transport only happens in plants.
    • D. Osmosis needs energy from respiration.

  4. Question 4

    What do diffusion and osmosis have in common?

    • A. Both move only water
    • B. Both are passive: they need no energy from respiration
    • C. Both need mitochondria
    • D. Both move substances against a gradient

  5. Question 5

    Which process is this: a raisin swelling in water?

    • A. diffusion
    • B. osmosis
    • C. active transport

  6. Question 6

    Root hair cells contain many mitochondria. What does this suggest?

    • A. They do not respire
    • B. They use active transport, which needs energy
    • C. They absorb water only by diffusion
    • D. They photosynthesise

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Answer key: Diffusion, osmosis or active transport?

  1. 1. C. active transport of mineral ions

  2. 2. C. active transport

  3. 3. B. Active transport can move substances from a low to a high concentration.

  4. 4. B. Both are passive: they need no energy from respiration

  5. 5. B. osmosis

  6. 6. B. They use active transport, which needs energy