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IGCSEBiology
Trial Class

Original practice · 5 questions · 15 marks · about 17 minutes

Gas Exchange and Air Composition 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 compare the composition of inhaled and exhaled air, and explore gas exchange in both animals and plants.

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 Both 4 marks Difficulty 3/5

    Compare the composition of inspired (inhaled) air and expired (exhaled) air in terms of oxygen, carbon dioxide, and water vapour.

    Show model answer and marking guidance
    1. Oxygen: higher in inspired air (~21%) than expired air (~16%).
    2. Carbon dioxide: lower in inspired air (~0.04%) than expired air (~4%).
    3. Water vapour: lower in inspired air than expired air (lungs add moisture).
    4. Nitrogen: approximately the same in both (~79%).

  2. Question 2

    Paper 4 Both 3 marks Difficulty 3/5

    Describe an experiment to show that exhaled air contains more carbon dioxide than inhaled air.

    Show model answer and marking guidance
    1. Breathe in through one tube and out through another: both passing through limewater.
    2. The limewater on the exhaled side turns milky/cloudy faster.
    3. This shows more CO₂ in exhaled air: CO₂ turns limewater milky.

  3. Question 3

    Paper 4 Extended 3 marks Difficulty 3/5

    Explain why expired air contains less oxygen than inspired air.

    Show model answer and marking guidance
    1. Oxygen diffuses from the alveoli into the blood.
    2. It is used by cells for aerobic respiration.
    3. So less oxygen remains in the air when it is breathed out.

  4. Question 4

    Paper 4 Extended 3 marks Difficulty 4/5

    Describe how gas exchange occurs in the leaves of plants.

    Show model answer and marking guidance
    1. During the day: CO₂ diffuses in through stomata for photosynthesis; O₂ diffuses out as a product.
    2. At night: O₂ diffuses in through stomata for respiration; CO₂ diffuses out.
    3. Gases dissolve in the moist film on mesophyll cell surfaces before diffusing across.

  5. Question 5

    Paper 2 Core 2 marks Difficulty 1/5

    Explain why expired air can turn limewater milky.

    Show model answer and marking guidance
    1. Expired air contains carbon dioxide.
    2. Carbon dioxide reacts with limewater (calcium hydroxide) to form a white precipitate (calcium carbonate).

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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