Surface Area to Volume Ratio and Exchange Surfaces · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Small shapes swap faster

Science · Organisms & Life Processes · ages 14-16
Name ______________________   Date ____________

  1. What happens to the ratio as cubes get larger?

    • It falls as the cube gets bigger
    • It rises as the cube gets bigger
    • It stays exactly the same
    • It doubles with each centimetre

  2. A cube has sides 2 cm long. What is its surface area to volume ratio?

    Answer: ______________

  3. A cube has sides 2 cm long. What is its surface area to volume ratio?

    Answer: ______________

  4. Why does a single-celled organism manage with no lungs?

    • It does not need gases
    • Diffusion across its membrane is enough
    • It holds its breath

  5. Two animals share the same shape but one is ten times bigger. Which needs special exchange surfaces?

    • The smaller one
    • Neither needs them
    • The bigger one

  6. A cube has sides 5 cm long. What is its surface area to volume ratio?

    Answer: ______________

  7. A cube has sides 4 cm long. What is its surface area to volume ratio?

    Answer: ______________

  8. A cube has sides 4 cm long. What is its surface area to volume ratio?

    Answer: ______________

  9. A pupil works out a 3 cm cube: area 54, volume 27, ratio 0.5. What went wrong?

    • They measured the sides wrong
    • Ratios cannot be whole numbers
    • Divided the wrong way round

  10. Why do lungs hold about 75 square metres of tiny air sacs?

    • To give diffusion a huge area
    • To store extra blood
    • To warm the air faster
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Small shapes swap faster W1-mt_1TclgVUxfa-s1

  1. It falls as the cube gets bigger · Volume grows faster than area, so the ratio drops with size.
  2. 3 · Faces give 6 x 4 = 24, volume is 8, and 24/8 = 3.
  3. 3 · Faces give 6 times 4, which is 24, volume is 8, and 24 divided by 8 is 3.
  4. Diffusion across its membrane is enough · Its ratio is so large that diffusion across the membrane supplies the whole cell.
  5. The bigger one · The bigger animal has the smaller ratio, so diffusion alone cannot supply it.
  6. 1.2 · Faces give 6 x 25 = 150, volume is 125, and 150/125 = 1.2.
  7. 1.5 · Faces give 6 x 16 = 96, volume is 64, and 96/64 = 1.5.
  8. 1.5 · Faces give 6 times 16, which is 96, volume is 64, and 96 divided by 64 is 1.5.
  9. Divided the wrong way round · The ratio is area divided by volume: 54 divided by 27 is 2, not 0.5.
  10. To give diffusion a huge area · Millions of sacs build an enormous area, which raises the gas exchange rate.
Worksheet · LightMySky