Explain how carbon stored in fossil fuels is returned to the atmosphere and why this contributes to an increase in atmospheric carbon dioxide levels.

Cambridge International IGCSE Biology (0610) — 19.3 Nutrient cycles · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

1. Fossil fuels are burned in combustion reactions.
2. Combustion releases CO₂ into the atmosphere.
3. Deforestation reduces the number of trees that can take up CO₂ via photosynthesis.
4. CO₂ cannot be removed or broken down as quickly as it is released, so atmospheric levels rise.

Examiner tips

Use the word ‘combustion’ and mention CO₂ release; link deforestation to reduced photosynthesis; explain the imbalance between release and removal; keep each point brief and to the point.

Common mistakes

Confusing combustion with photosynthesis; omitting the role of deforestation; failing to state that CO₂ removal is slower than release; using vague terms like ‘burning’ without specifying CO₂ output.

Mark scheme (4 marks)

Fossil fuels are burned / combustion of fossil fuels occurs
Combustion releases carbon dioxide into the atmosphere
Deforestation reduces the number of trees / plants available to remove carbon dioxide by photosynthesis
Carbon dioxide cannot be removed / broken down as quickly as it is being released, so levels increase

Key terms in this question

fossil fuel