A wildlife organisation is investigating the carbon cycle in a woodland ecosystem. The woodland contains producers, primary consumers, secondary consumers, and decomposers. Explain how carbon moves from the atmosphere into living organisms and then back into the atmosphere in this woodland ecosystem.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Carbon is continuously cycled through the biotic and abiotic components of ecosystems. In a woodland, this cycling involves several different biological processes and groups of organisms.
Model answer (5 marks)
1. Producers (plants) absorb CO₂ from the atmosphere during photosynthesis, converting it into organic carbon in their tissues.
2. Primary consumers eat the producers, taking the stored carbon into their bodies.
3. Secondary consumers eat the primary consumers, transferring the carbon further up the food chain.
4. When any of these organisms respire, they oxidise the organic carbon, releasing CO₂ back into the atmosphere.
5. Decomposers break down dead plants and animals, and through decomposition and their own respiration they also return CO₂ to the air; combustion of organic matter can additionally release CO₂.
2. Primary consumers eat the producers, taking the stored carbon into their bodies.
3. Secondary consumers eat the primary consumers, transferring the carbon further up the food chain.
4. When any of these organisms respire, they oxidise the organic carbon, releasing CO₂ back into the atmosphere.
5. Decomposers break down dead plants and animals, and through decomposition and their own respiration they also return CO₂ to the air; combustion of organic matter can additionally release CO₂.
Examiner tips
- Use the exact terms: photosynthesis, respiration, decomposers, combustion; show the flow from atmosphere → producers → consumers → atmosphere.
- Number your points to match the five marks and keep each point concise.
Mark scheme (5 marks)
- Carbon dioxide is removed from the atmosphere by producers (plants) through photosynthesis
- Carbon passes along the food chain when consumers eat producers (or other consumers)
- Carbon dioxide is returned to the atmosphere when living organisms respire
- Decomposers break down dead organisms / decaying matter, releasing carbon dioxide through decomposition / respiration
- Carbon can also be returned to the atmosphere through combustion of organic matter
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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