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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 3.6 g. What is the percentage change in mass? (Use a minus sign for a loss.) → 12.5 %Prompt: percentage change = (final − initial) ÷ initial × 100
  2. Potato pieces were left in sugar solutions. Percentage change in mass: 0 mol/dm³: +28 % 0.2 mol/dm³: +20 % 0.4 mol/dm³: +12 % 0.6 mol/dm³: +4 % 0.8 mol/dm³: −4 % 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) → 0.6–0.8 mol/dm³Prompt: Where there is no net movement of water, the mass does not change.
  3. Cucumber slices sprinkled with salt become limp and watery. Why? (Water leaves the cells by osmosis into the more concentrated salty surface / Salt particles push water out by force / Salt enters and the cells burst / The cucumber starts to photosynthesise) → Water leaves the cells by osmosis into the more concentrated salty surfacePrompt: Water moves from a dilute solution to a more concentrated one.

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: mineral ions entering root hairs from soil with fewer ions? (diffusion / osmosis / active transport) → active transportPrompt: Is it water specifically? Is it going against the gradient?
  2. What do diffusion and osmosis have in common? (Both move only water / Both move substances against a gradient / Both need mitochondria / Both are passive: they need no energy from respiration) → 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. 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. Glucose is absorbed from the small intestine even when the blood already holds more glucose than the gut. How? (it cannot be absorbed / by osmosis / by diffusion down the gradient / by active transport, using energy from respiration) → by active transport, using energy from respirationPrompt: The glucose is moving against its gradient.

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

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Diffusion, osmosis or active transport?

Name

Date

Score/ 6

  1. Question 1

    Transport in cells: which statement is true?

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

  2. Question 2

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

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

  3. Question 3

    Which process is this: carbon dioxide entering a leaf?

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

  4. Question 4

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

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

  5. Question 5

    Which process is this: mineral ions entering root hairs from soil with fewer ions?

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

  6. Question 6

    Which process is this: water entering root hair cells from moist soil?

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

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Answer key: Diffusion, osmosis or active transport?

  1. 1. C. Active transport needs energy from respiration.

  2. 2. C. active transport of mineral ions

  3. 3. A. diffusion

  4. 4. C. They use active transport, which needs energy

  5. 5. C. active transport

  6. 6. B. osmosis