Explain how the structure of a leaf is adapted to allow transpiration to occur.

Cambridge International IGCSE Biology (0610) — 8.3 Transpiration · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Stomata on the leaf surface allow water vapour to diffuse out.
Air spaces in the spongy mesophyll become saturated with water vapour, creating a high internal concentration.
The inter‑connecting air spaces give a large internal surface area, so more water can evaporate.
A concentration gradient of water vapour between the inside and outside of the leaf drives the diffusion of water vapour outwards.

Examiner tips

  • Use the word ‘stomata’ and ‘spongy mesophyll’ – these are key terms. Show the cause–effect chain: stomata → high internal vapour → gradient → diffusion. Keep the answer concise, 4–5 short sentences.
  • common_mistakes
  • :
  • Forgetting to mention stomata or the spongy mesophyll. Using vague phrases like ‘leaf surface’ without specifying stomata. Failing to explain the concentration gradient or the role of internal surface area.

Mark scheme (4 marks)

  1. Stomata are present on the leaf surface, allowing water vapour to diffuse out
  2. Air spaces in the spongy mesophyll become saturated with water vapour, maintaining a high concentration of water vapour inside the leaf
  3. The interconnecting air spaces create a large internal surface area, increasing the amount of water that can evaporate
  4. A concentration gradient of water vapour exists between the inside and outside of the leaf, so water vapour diffuses out

Key terms in this question

transpiration

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