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IGCSEBiology
Trial Class

Original practice · 5 questions · 16 marks · about 18 minutes

Nutrient Cycles Practice Questions

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

These questions test your understanding of how carbon and nitrogen are recycled through ecosystems.

Before you open the answers

  • Attempt every question without notes.
  • Show working for calculations and write complete biological statements.
  • Use the suggested time as a guide, not a strict limit on the first attempt.

These are original practice questions. They do not reproduce an official Cambridge paper or official mark scheme.

  1. Question 1

    Paper 4 Extended 4 marks Difficulty 4/5

    Describe four processes involved in the carbon cycle.

    Show model answer and marking guidance
    1. Photosynthesis removes CO₂ from the atmosphere: plants convert it to glucose.
    2. Respiration by all living organisms returns CO₂ to the atmosphere.
    3. Combustion (burning) of fossil fuels releases stored carbon as CO₂.
    4. Decomposition: decomposers break down dead organisms, releasing CO₂ through respiration.

  2. Question 2

    Paper 4 Both 3 marks Difficulty 3/5

    Explain the role of decomposers in nutrient cycling.

    Show model answer and marking guidance
    1. Decomposers (bacteria and fungi) break down dead organisms and waste.
    2. They release nutrients (e.g. Mineral ions) back into the soil.
    3. These nutrients can then be absorbed by plant roots: recycling them through the ecosystem.

  3. Question 3

    Paper 4 Extended 4 marks Difficulty 4/5

    Describe the role of the following bacteria in the nitrogen cycle: (a) nitrogen-fixing bacteria, (b) nitrifying bacteria, (c) denitrifying bacteria.

    Show model answer and marking guidance
    1. (a) Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia/ammonium compounds: found in root nodules of legumes or in soil.
    2. (b) Nitrifying bacteria convert ammonium compounds to nitrites, then to nitrates: making nitrogen available for plant uptake.
    3. (c) Denitrifying bacteria convert nitrates back to nitrogen gas: returning it to the atmosphere.
    4. Decomposers also contribute by converting dead organic matter to ammonium compounds.

  4. Question 4

    Paper 2 Core 2 marks Difficulty 2/5

    Name the process that removes carbon dioxide from the atmosphere.

    Show model answer and marking guidance
    1. Photosynthesis.
    2. Plants use CO₂ and water to make glucose, releasing oxygen.

  5. Question 5

    Paper 4 Extended 3 marks Difficulty 4/5

    Explain why the burning of fossil fuels is disrupting the carbon cycle.

    Show model answer and marking guidance
    1. Fossil fuels contain carbon that was locked underground for millions of years.
    2. Burning releases this stored carbon as CO₂ rapidly: faster than photosynthesis can remove it.
    3. This increases the concentration of CO₂ in the atmosphere, contributing to the enhanced greenhouse effect / global warming.

Mark the set consistently

Award a point only when the idea is clearly present in the written answer. Correct any missed point in a complete sentence, then test the same skill on a different question several days later.

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