Describe the role of stomata in the excretion of waste gases from the leaves of a flowering plant.

Pearson Edexcel International GCSE Biology (4BI1) — 2.12 Excretion: flowering plants · Describe · 4 marks · View as Markdown

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

Flowering plants produce waste gases as by-products of metabolism. These gases must be removed from the plant body.

Model answer (4 marks)

1. Carbon dioxide produced by aerobic respiration is a waste gas.
2. Oxygen produced during photosynthesis is also a waste gas.
3. Both gases leave the leaf by diffusion.
4. Stomata are pores in the leaf epidermis that open and close to control gas exchange.

Examiner tips

  • Use the exact terms ‘carbon dioxide’, ‘oxygen’, ‘diffusion’, ‘stomata’, ‘pores’, ‘epidermis’, ‘open and close’.
  • Show the four points clearly, each worth one mark.
  • Mention that stomata are the route for gas movement.
  • Keep the answer concise and to the point.

Common mistakes

  • Confusing stomata with other leaf structures such as trichomes.
  • Lumping all gases together without specifying CO₂ and O₂.
  • Using vague words like ‘air’ instead of ‘gases’ or ‘diffusion’.

Mark scheme (4 marks)

  1. Carbon dioxide is a waste product of (aerobic) respiration in flowering plants
  2. Oxygen is a waste product of photosynthesis in flowering plants
  3. Waste gases move out of the leaf by diffusion (through the stomata)
  4. Stomata are pores / openings (in the leaf surface / epidermis) that allow gas exchange / that open and close to control the movement of gases

Key terms in this question

stomata · excretion

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