Explain how the structure of a leaf is adapted to allow efficient gas exchange in a flowering plant.

Pearson Edexcel International GCSE Biology (4BI1) — 2.8 Gas exchange: flowering plants · 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 in the lower epidermis allow CO₂ to enter and O₂ to leave the leaf by diffusion.
The leaf has a large surface area, which increases the area over which diffusion can occur.
Air spaces in the spongy mesophyll allow gases to circulate and diffuse throughout the leaf.
The waxy cuticle is thin or absent on the lower surface, so it does not block gas exchange and reduces water loss from the upper surface.

Examiner tips

  • Use the word ‘stomata’ and mention the lower epidermis. Mention large surface area and air spaces. Explain the role of the cuticle. Keep the answer concise and use correct terminology.

Common mistakes

  • Forgetting to state that stomata are on the lower epidermis. Describing the cuticle as thick or blocking gas exchange. Omitting the role of air spaces in the spongy mesophyll.

Mark scheme (4 marks)

  1. Stomata are present (in the lower epidermis) and allow gases to enter and leave the leaf by diffusion
  2. The leaf has a large surface area, increasing the area over which diffusion can occur
  3. Air spaces in the spongy mesophyll allow gases to circulate / diffuse throughout the leaf
  4. The waxy cuticle is thin / absent on the lower surface, so it does not prevent gas exchange / reduces water loss from the upper surface without blocking gas exchange

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