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IGCSEBiology
Trial Class

Original practice · 5 questions · 17 marks · about 19 minutes

Limiting Factors of Photosynthesis 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 ability to interpret graphs and explain how light intensity, carbon dioxide concentration, and temperature act as limiting factors.

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

    A graph shows that the rate of photosynthesis increases as light intensity increases, then levels off at a plateau. Explain the shape of this graph.

    Show model answer and marking guidance
    1. At low light intensity, light is the limiting factor: increasing light increases the rate.
    2. At the plateau, another factor becomes limiting (e.g. CO₂ concentration or temperature).
    3. Increasing light beyond this point does not increase the rate further.
    4. All available CO₂ is being used / enzymes are working at maximum rate.

  2. Question 2

    Paper 4 Both 3 marks Difficulty 3/5

    State three factors that can limit the rate of photosynthesis.

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    1. Light intensity.
    2. Carbon dioxide concentration.
    3. Temperature.

  3. Question 3

    Paper 4 Extended 4 marks Difficulty 4/5

    A greenhouse owner wants to maximise plant growth. Suggest three ways they could increase the rate of photosynthesis and explain how each works.

    Show model answer and marking guidance
    1. Increase light intensity with artificial lights: more light energy for photosynthesis.
    2. Add CO₂ (e.g. From a gas burner): increases raw material supply for the reaction.
    3. Heat the greenhouse to ~25–30°C: enzyme activity increases but avoid too high (denaturation).
    4. Water plants adequately: water is a raw material for photosynthesis.

  4. Question 4

    Paper 4 Extended 3 marks Difficulty 3/5

    Explain why very high temperatures (above 40°C) decrease the rate of photosynthesis.

    Show model answer and marking guidance
    1. Enzymes involved in photosynthesis begin to denature.
    2. The active sites change shape and substrates can no longer bind.
    3. Stomata may close to prevent water loss, reducing CO₂ entry.

  5. Question 5

    Paper 4 Both 3 marks Difficulty 3/5

    Define the term "limiting factor" in the context of photosynthesis.

    Show model answer and marking guidance
    1. A limiting factor is the factor that is in shortest supply / lowest quantity.
    2. It directly controls / restricts the rate of photosynthesis.
    3. Increasing the limiting factor will increase the rate; increasing other factors will not.

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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