Explain how the spongy mesophyll and stomata work together to allow efficient gas exchange in a leaf.

Cambridge International IGCSE Biology (0610) — 6.2 Leaf structure · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Spongy mesophyll contains large intercellular air spaces that give a high surface area for diffusion.
Carbon dioxide from the atmosphere diffuses rapidly through these air spaces to the chloroplasts, while oxygen produced in photosynthesis diffuses back out.
Stomata are pores on the leaf surface that provide the entry and exit points for gases.
Guard cells surrounding each stoma control its opening and closing, regulating gas exchange and minimising water loss.

Examiner tips

  • Use the word ‘diffuse’ to show understanding of gas movement.
  • Mention that guard cells control stomatal aperture to link gas exchange with water regulation.
  • Keep the answer concise – one sentence per point.
  • Use UK spelling (e.g. ‘mesophyll’).

Common mistakes

  • Confusing spongy mesophyll with palisade mesophyll.
  • Forgetting to mention guard cells or their role in regulating stomata.
  • Using vague terms like ‘allows gas movement’ instead of ‘diffuses’.

Mark scheme (4 marks)

  1. Spongy mesophyll has air spaces that increase surface area for diffusion
  2. Carbon dioxide (and oxygen) diffuse rapidly through the air spaces of the spongy mesophyll
  3. Stomata are pores / openings that allow gases to enter and leave the leaf
  4. Guard cells control the opening and closing of stomata to regulate gas exchange (and water loss)

Key terms in this question

spongy mesophyll · stomata

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