Describe the role of microorganisms in the carbon cycle.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Microorganisms decompose dead organic matter, releasing carbon as carbon dioxide during their respiration. This CO₂ is returned to the atmosphere, allowing the carbon to be recycled and reused by plants in photosynthesis.
Examiner tips
- Use the word ‘decompose’ and mention ‘dead organic matter’ to hit the first point. Show the link between microbial respiration and CO₂ release. Explain that CO₂ returns to the atmosphere and is taken up by plants. Keep the answer concise – 4 points, 1–2 sentences each.
Common mistakes
- Confusing microbial activity with plant photosynthesis. Forgetting to mention the return of CO₂ to the atmosphere. Using vague terms like ‘break down’ without specifying ‘dead organic matter’.
Mark scheme (4 marks)
- Microorganisms decompose/break down dead organic matter (organisms/plants/animals)
- Carbon is released as carbon dioxide during respiration by microorganisms
- This returns carbon (dioxide) to the atmosphere
- This process allows carbon to be recycled / reused by plants (for photosynthesis)
Key terms in this question
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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