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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 packed in a regular pattern? (solid / liquid / gas) → solidPrompt: How close are the particles, and how do they move?
  2. What happens to particles when a substance is heated? (They get bigger / They melt / They move faster / They stop moving) → They move fasterPrompt: Heating gives particles more energy.
  3. 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?

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. Carbon dioxide made by respiring cells moves into the blood. Which way is the gradient? (higher in the cells, lower in the blood / there is no carbon dioxide in cells / the same on both sides / higher in the blood, lower in the cells) → higher in the cells, lower in the bloodPrompt: Where is carbon dioxide being made?
  2. Agar cubes containing indicator were put into acid. Time for the whole cube to change colour: 1 cm cube 6 min, 2 cm cube 16 min, 3 cm cube 18 min. Which cube's centre was reached fastest by the acid? (the 1 cm cube / the 2 cm cube / the 3 cm cube) → the 1 cm cubePrompt: Fastest means the shortest 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. Diffusion: which statement is NOT true? (Particles stop moving once they are evenly spread. / Diffusion happens in gases and liquids. / Diffusion does not need energy from respiration. / A steeper concentration gradient gives faster diffusion.) → Particles stop moving once they are evenly spread.Prompt: Which direction is the net movement?
  2. Carbon dioxide made by respiring cells moves into the blood. Which way is the gradient? (the same on both sides / higher in the cells, lower in the blood / higher in the blood, lower in the cells / there is no carbon dioxide in cells) → higher in the cells, lower in the bloodPrompt: Where is carbon dioxide being made?

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

    Purple dye spread 8 mm through a block of jelly in 3 hours. What was the mean rate of diffusion, in mm per hour?

    Answermm/h

  2. Question 2

    Diffusion: which statement is NOT true?

    • A. Diffusion happens in gases and liquids.
    • B. Diffusion moves particles from low to high concentration.
    • C. A steeper concentration gradient gives faster diffusion.
    • D. A larger surface area speeds up diffusion.

  3. Question 3

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

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

  4. Question 4

    Purple dye spread 12 mm through a block of jelly in 2 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. there is no carbon dioxide in cells
    • C. the same on both sides
    • D. higher in the blood, lower in the cells

  6. Question 6

    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 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

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Answer key: Diffusion: how particles spread out

  1. 1. 2.7 mm/h

  2. 2. B. Diffusion moves particles from low to high concentration.

  3. 3. A. Perfume particles diffuse from high to low concentration

  4. 4. 6 mm/h

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

  6. 6. A. the 1 cm cube