Describe how carbon is cycled between the atmosphere and living organisms, including the roles of photosynthesis, respiration, decomposition and combustion.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Carbon dioxide is taken up from the atmosphere by plants during photosynthesis and incorporated into organic molecules such as carbohydrates and proteins.
Carbon is transferred through the food chain when organisms feed on one another, passing it between trophic levels.
Carbon is returned to the atmosphere as carbon dioxide by respiration in all living organisms, including plants, animals and decomposers.
Carbon stored in fossil fuels is released as carbon dioxide when it is combusted, or carbon in dead organisms is returned to the atmosphere by decomposition.
Carbon is transferred through the food chain when organisms feed on one another, passing it between trophic levels.
Carbon is returned to the atmosphere as carbon dioxide by respiration in all living organisms, including plants, animals and decomposers.
Carbon stored in fossil fuels is released as carbon dioxide when it is combusted, or carbon in dead organisms is returned to the atmosphere by decomposition.
Examiner tips
- Use the exact terms ‘photosynthesis’, ‘respiration’, ‘decomposition’, ‘combustion’
- Show the direction of carbon flow in each process
- Include both biotic and abiotic reservoirs
Common mistakes
- Confusing photosynthesis with respiration
- Omitting the role of decomposition or combustion
- Using vague phrases like ‘carbon moves’ instead of specific processes
Mark scheme (4 marks)
- Carbon dioxide is removed from the atmosphere by plants during photosynthesis and incorporated into organic molecules such as carbohydrates or proteins.
- Carbon is passed through the food chain when organisms feed on one another / is transferred between trophic levels by feeding / ingestion.
- Carbon is returned to the atmosphere as carbon dioxide by respiration in living organisms (plants, animals and decomposers).
- Carbon stored in fossil fuels is released as carbon dioxide by combustion, OR carbon in dead organisms is returned to the atmosphere by decomposition.
Key terms in this question
photosynthesis · respiration · decomposition · combustion
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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