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Science lesson plan · 7th grade (Year 8 in England) · 45 minutes

Diffusion: how particles spread out

Cells, genetics and evolution

CCSS NGSS.MS-LS1-2CCSS NGSS.MS-PS1-4England: KS3 Biology: Cells and organisationEngland: GCSE Combined Science: Cell biology

Objective and success criteria

Students will: Diffusion: how particles spread out.

  • 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: The particle model; Plant and animal cells

Leads to: Osmosis and percentage change in mass; Surface area to volume ratio and exchange

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

Warm-up · 5 min

  • Quick retrieval from earlier learning (The particle model; Plant and animal cells). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Which state is described: particles close together in a random arrangement? (solid / liquid / gas) → liquidPrompt: How close are the particles, and how do they move?
  2. Why can't solids flow? (Their particles are far apart / Their particles move very fast / Their particles are held in fixed positions / Their particles do not exist) → Their particles are held in fixed positionsPrompt: Can solid particles swap places?
  3. Which state is described: particles far apart moving quickly in all directions? (solid / liquid / gas) → gasPrompt: How close are the particles, and how do they move?

Hook · 5 min

  • Show a microscope image of cells and ask what students think they are looking at.
  • Share the objective: Diffusion: how particles spread out. Read the success criteria together.

I do: model it · 10 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: Carbon dioxide made by respiring cells moves into the blood. Which way is the gradient?
  • Step 1: Cells make carbon dioxide, so it diffuses from cells into the blood.
  • Step 2: So the answer is: higher in the cells, lower in the blood
  • Answer: higher in the cells, lower in the blood
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 10 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. Oxygen moves from the alveoli into the blood. Why? (Oxygen is heavier than blood / Blood pulls oxygen like a magnet / The heart pushes air in / There is more oxygen in the alveoli than in the blood) → There is more oxygen in the alveoli than in the bloodPrompt: Compare the concentration on each side.
  2. Purple dye spread 6 mm through a block of jelly in 2 hours. What was the mean rate of diffusion, in mm per hour? → 3 mm/hPrompt: rate = distance ÷ time

You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 5 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. Carbon dioxide made by respiring cells moves into the blood. Which way is the gradient? (higher in the cells, lower in the blood / the same on both sides / there is no carbon dioxide in cells / higher in the blood, lower in the cells) → higher in the cells, lower in the bloodPrompt: Where is carbon dioxide being made?
  2. Diffusion: which statement is NOT true? (Diffusion does not need energy from respiration. / Diffusion stops completely when the room is cold. / A steeper concentration gradient gives faster diffusion. / A larger surface area speeds up diffusion.) → Diffusion stops completely when the room is cold.Prompt: Which direction is the net movement?

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: The particle model.
  • 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: Osmosis and percentage change in mass; Surface area to volume ratio and exchange.
  • 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-7.

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

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Diffusion: how particles spread out

Name

Date

Score/ 8

  1. Question 1

    Diffusion: which statement is NOT true?

    • A. A larger surface area speeds up diffusion.
    • B. Diffusion does not need energy from respiration.
    • C. Particles stop moving once they are evenly spread.
    • D. Diffusion happens in gases and liquids.

  2. Question 2

    Which change would make diffusion faster?

    • A. a smaller surface area
    • B. a thicker membrane
    • C. a lower temperature
    • D. a higher temperature

  3. Question 3

    Agar cubes containing indicator were put into acid. Time for the whole cube to change colour: 1 cm cube 8 min, 2 cm cube 12 min, 3 cm cube 24 min. Which cube's centre was reached fastest by the acid?

    • A. the 1 cm cube
    • B. the 2 cm cube
    • C. the 3 cm cube

  4. Question 4

    Purple dye spread 15 mm through a block of jelly in 3 hours. What was the mean rate of diffusion, in mm per hour?

    Answermm/h

  5. Question 5

    Carbon dioxide made by respiring cells moves into the blood. Which way is the gradient?

    • A. higher in the cells, lower in the blood
    • B. higher in the blood, lower in the cells
    • C. the same on both sides
    • D. there is no carbon dioxide in cells

  6. Question 6

    Purple dye spread 8 mm through a block of jelly in 2 hours. What was the mean rate of diffusion, in mm per hour?

    Answermm/h

  7. Question 7

    Someone opens a bottle of perfume in one corner of a still room. Soon it is smelled everywhere. Why?

    • A. Perfume particles are pulled by gravity
    • B. Perfume particles diffuse from high to low concentration
    • C. The perfume becomes a solid
    • D. Air particles stop moving

  8. Question 8

    Oxygen moves from the alveoli into the blood. Why?

    • A. There is more oxygen in the alveoli than in the blood
    • B. Oxygen is heavier than blood
    • C. The heart pushes air in
    • D. Blood pulls oxygen like a magnet

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Answer key: Diffusion: how particles spread out

  1. 1. C. Particles stop moving once they are evenly spread.

  2. 2. D. a higher temperature

  3. 3. A. the 1 cm cube

  4. 4. 5 mm/h

  5. 5. A. higher in the cells, lower in the blood

  6. 6. 4 mm/h

  7. 7. B. Perfume particles diffuse from high to low concentration

  8. 8. A. There is more oxygen in the alveoli than in the blood