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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 in fixed positions that only vibrate? (solid / liquid / gas) → solidPrompt: How close are the particles, and how do they move?
  2. Why does the smell of perfume spread across a room? (Perfume particles are attracted to noses / Air particles stand still / Perfume particles diffuse, moving randomly among the air particles / The perfume pushes the air away) → Perfume particles diffuse, moving randomly among the air particlesPrompt: Particles in gases move in all directions.
  3. Which state is described: particles packed in a regular pattern? (solid / liquid / gas) → solidPrompt: 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. Which change would make diffusion faster? (a thicker membrane / a lower temperature / a higher temperature / a smaller surface area) → a higher temperaturePrompt: Think about how fast the particles move.
  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? → 4 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. Diffusion: which statement is NOT true? (Diffusion happens in gases and liquids. / Diffusion stops completely when the room is cold. / Diffusion does not need energy from respiration. / A larger surface area speeds up diffusion.) → Diffusion stops completely when the room is cold.Prompt: Which direction is the net movement?
  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 12 min, 3 cm cube 24 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.

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

    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

  2. Question 2

    Diffusion: which statement is NOT true?

    • A. Diffusion stops completely when the room is cold.
    • B. A steeper concentration gradient gives faster diffusion.
    • C. A larger surface area speeds up diffusion.
    • D. Diffusion does not need energy from respiration.

  3. Question 3

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

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

  4. Question 4

    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

  5. Question 5

    Which change would make diffusion faster?

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

  6. Question 6

    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

  7. Question 7

    Oxygen moves from the alveoli into the blood. Why?

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

  8. Question 8

    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

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Answer key: Diffusion: how particles spread out

  1. 1. A. the 1 cm cube

  2. 2. A. Diffusion stops completely when the room is cold.

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

  4. 4. 2.7 mm/h

  5. 5. B. a higher temperature

  6. 6. 3 mm/h

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

  8. 8. A. the 1 cm cube