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Science lesson plan · 7th grade (Year 8 in England) · 60 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 · 6 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 with lots of empty space between them? (solid / liquid / gas) → gasPrompt: 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 close together in a random arrangement? (solid / liquid / gas) → liquidPrompt: How close are the particles, and how do they move?

Hook · 6 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 · 12 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 · 12 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? (There is more oxygen in the alveoli than in the blood / Oxygen is heavier than blood / The heart pushes air in / Blood pulls oxygen like a magnet) → There is more oxygen in the alveoli than in the bloodPrompt: Compare the concentration on each side.
  2. Purple dye spread 12 mm through a block of jelly in 2 hours. What was the mean rate of diffusion, in mm per hour? → 6 mm/hPrompt: rate = distance ÷ time

You do: independent practice · 17 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 · 7 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. 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? (the 1 cm cube / the 2 cm cube / the 3 cm cube) → the 1 cm cubePrompt: Fastest means the shortest time.
  2. Diffusion: which statement is NOT true? (Particles stop moving once they are evenly spread. / A steeper concentration gradient gives faster diffusion. / Diffusion happens in gases and liquids. / Diffusion does not need energy from respiration.) → Particles stop moving once they are evenly spread.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

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

  2. Question 2

    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 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

  3. Question 3

    Diffusion: which statement is NOT true?

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

  4. Question 4

    Which change would make diffusion faster?

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

  5. Question 5

    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 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

  6. Question 6

    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

  7. Question 7

    Purple dye spread 15 mm through a block of jelly in 2 hours. What was the mean rate of diffusion, in mm per hour?

    Answermm/h

  8. Question 8

    Oxygen moves from the alveoli into the blood. Why?

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

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Answer key: Diffusion: how particles spread out

  1. 1. D. higher in the cells, lower in the blood

  2. 2. A. the 1 cm cube

  3. 3. A. Diffusion moves particles from low to high concentration.

  4. 4. B. a higher temperature

  5. 5. A. the 1 cm cube

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

  7. 7. 7.5 mm/h

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