Describe how oxygen produced during photosynthesis is removed from a flowering plant as a waste product of metabolism.

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 carry out photosynthesis, producing oxygen as a waste product. This oxygen must be removed from the plant body.

Model answer (4 marks)

Oxygen produced in the chloroplasts diffuses out of the leaf through the stomata.
The movement is driven by a concentration gradient – oxygen concentration is higher inside the leaf than in the surrounding air.
Stomata are small pores mainly on the lower leaf surface that allow gas exchange.
Only the excess oxygen (net surplus) is released; some is used in the plant’s respiration.

Examiner tips

  • Use the word ‘diffuses’ and mention ‘stomata’ to hit two marks. Explain the concentration gradient to gain a third mark. State that only excess oxygen is released to earn the final mark.

Common mistakes

  • Confusing oxygen with carbon dioxide. Forgetting to mention the stomata. Failing to note that only the surplus oxygen is expelled.

Mark scheme (4 marks)

  1. Oxygen diffuses out of the leaf (through the stomata)
  2. Diffusion occurs down a concentration gradient, from higher concentration inside the leaf to lower concentration outside
  3. Stomata are pores / openings found mainly on the lower surface of the leaf
  4. Some oxygen is used in respiration within the plant (so only the excess / net surplus is removed as waste)

Key terms in this question

photosynthesis

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