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Science lesson plan · 7th grade (Year 8 in England) · 30 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 · 4 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 touching but able to slide past each other? (solid / liquid / gas) → liquidPrompt: How close are the particles, and how do they move?
  2. Why does the smell of perfume spread across a room? (The perfume pushes the air away / Perfume particles diffuse, moving randomly among the air particles / Perfume particles are attracted to noses / Air particles stand still) → Perfume particles diffuse, moving randomly among the air particlesPrompt: Particles in gases move in all directions.
  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 · 3 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 · 7 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 · 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. Someone opens a bottle of perfume in one corner of a still room. Soon it is smelled everywhere. Why? (Air particles stop moving / Perfume particles diffuse from high to low concentration / Perfume particles are pulled by gravity / The perfume becomes a solid) → Perfume particles diffuse from high to low concentrationPrompt: Particles move randomly and spread out.
  2. Purple dye spread 8 mm through a block of jelly in 2 hours. What was the mean rate of diffusion, in mm per hour? → 4 mm/hPrompt: rate = distance ÷ time

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 change would make diffusion faster? (a higher temperature / a lower temperature / a thicker membrane / a smaller surface area) → a higher temperaturePrompt: Think about how fast the particles move.
  2. Diffusion: which statement is NOT true? (Diffusion moves particles from low to high concentration. / A larger surface area speeds up diffusion. / Diffusion happens in gases and liquids. / A steeper concentration gradient gives faster diffusion.) → Diffusion moves particles from low to high concentration.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/ 6

  1. Question 1

    Diffusion: which statement is NOT true?

    • A. A steeper concentration gradient gives faster diffusion.
    • B. Diffusion happens in gases and liquids.
    • C. A larger surface area speeds up diffusion.
    • D. Diffusion stops completely when the room is cold.

  2. Question 2

    Purple dye spread 12 mm through a block of jelly in 3 hours. What was the mean rate of diffusion, in mm per hour?

    Answermm/h

  3. Question 3

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

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

  4. Question 4

    Agar cubes containing indicator were put into acid. Time for the whole cube to change colour: 1 cm cube 6 min, 2 cm cube 12 min, 3 cm cube 18 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

  5. Question 5

    Purple dye spread 9 mm through a block of jelly in 3 hours. What was the mean rate of diffusion, in mm per hour?

    Answermm/h

  6. Question 6

    Which change would make diffusion faster?

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

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Answer key: Diffusion: how particles spread out

  1. 1. D. Diffusion stops completely when the room is cold.

  2. 2. 4 mm/h

  3. 3. B. higher in the cells, lower in the blood

  4. 4. A. the 1 cm cube

  5. 5. 3 mm/h

  6. 6. C. a higher temperature