Back to the lesson plan builder
Lesson length30 min45 min60 min
Questions🔀 New questions

Print the plan for yourself; the student sheet prints on its own page after it.

Science lesson plan · 8th grade (Year 9 in England) · 60 minutes

Surface area to volume ratio and exchange

Cells, genetics and evolution

CCSS NGSS.HS-LS1-2CCSS NGSS.SEP 5England: GCSE Combined Science: Cell biology (exchange surfaces)

Objective and success criteria

Students will: Surface area to volume ratio and exchange.

  • 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: Diffusion: how particles spread out

Leads to: the next skill in this area.

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 (Diffusion: how particles spread out). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. Carbon dioxide made by respiring cells moves into the blood. Which way is the gradient? (higher in the blood, lower in the cells / there is no carbon dioxide in cells / the same on both sides / higher in the cells, lower in the blood) → higher in the cells, lower in the bloodPrompt: Where is carbon dioxide being made?
  2. Purple dye spread 15 mm through a block of jelly in 2 hours. What was the mean rate of diffusion, in mm per hour? → 7.5 mm/hPrompt: rate = distance ÷ time
  3. Diffusion: which statement is NOT true? (A larger surface area speeds up diffusion. / Particles stop moving once they are evenly spread. / 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?

Hook · 6 min

  • Show a microscope image of cells and ask what students think they are looking at.
  • Share the objective: Surface area to volume ratio and exchange. 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: A cube-shaped cell model has sides of 3 cm. What is its surface area to volume ratio, written as ? : 1?
  • Step 1: surface area = 6 × 3 × 3 = 54 cm²
  • Step 2: volume = 3³ = 27 cm³
  • Step 3: 54 ÷ 27 = 2
  • Step 4: So the answer is: 2
  • Answer: 2
  • 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. A cube-shaped cell model has sides of 5 cm. What is its surface area to volume ratio, written as ? : 1? → 1.2Prompt: Surface area of a cube = 6 × side × side.
  2. An elephant has a much smaller surface area to volume ratio than a mouse. What problem does this cause? (Moving too fast / Losing heat quickly enough / Losing heat too quickly / Getting too little food) → Losing heat quickly enoughPrompt: Heat is lost through the surface.

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. A cube-shaped cell model has sides of 4 cm. What is its surface area to volume ratio, written as ? : 1? → 1.5Prompt: Surface area of a cube = 6 × side × side.
  2. Which feature does NOT increase the effectiveness of an exchange surface? (a thick wall / being ventilated / a large surface area / a good blood supply) → a thick wallPrompt: Diffusion needs a short path.

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: Diffusion: how particles spread out.
  • 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

  • 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-8.

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

eurekami

Surface area to volume ratio and exchange

Name

Date

Score/ 8

  1. Question 1

    Exchange surfaces: which statement is NOT true?

    • A. Large animals need transport systems to reach all their cells.
    • B. A larger cube has a larger surface area to volume ratio.
    • C. Villi increase the surface area of the small intestine.
    • D. Fish gills have many thin filaments to increase surface area.

  2. Question 2

    Why are the alveoli in the lungs so numerous and tiny?

    • A. to give a huge surface area for gas exchange
    • B. to store air for later
    • C. to filter out food
    • D. to make the lungs heavier

  3. Question 3

    A cube-shaped cell model has sides of 4 cm. What is its surface area to volume ratio, written as ? : 1?

    Answer

  4. Question 4

    An elephant has a much smaller surface area to volume ratio than a mouse. What problem does this cause?

    • A. Losing heat quickly enough
    • B. Moving too fast
    • C. Getting too little food
    • D. Losing heat too quickly

  5. Question 5

    A cube-shaped cell model has sides of 6 cm. What is its surface area to volume ratio, written as ? : 1?

    Answer

  6. Question 6

    Why does a large multicellular animal need lungs and a heart, but an amoeba does not?

    • A. Large animals do not use oxygen
    • B. Its small SA:V ratio and long distances mean diffusion alone is too slow
    • C. Amoebae are not alive
    • D. Diffusion is faster in big animals

  7. Question 7

    A cube-shaped cell model has sides of 1 cm. What is its surface area to volume ratio, written as ? : 1?

    Answer

  8. Question 8

    A cube-shaped cell model has sides of 3 cm. What is its surface area to volume ratio, written as ? : 1?

    Answer

Free from eurekami.com

for the adult only

Answer key: Surface area to volume ratio and exchange

  1. 1. B. A larger cube has a larger surface area to volume ratio.

  2. 2. A. to give a huge surface area for gas exchange

  3. 3. 1.5

  4. 4. A. Losing heat quickly enough

  5. 5. 1

  6. 6. B. Its small SA:V ratio and long distances mean diffusion alone is too slow

  7. 7. 6

  8. 8. 2