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IGCSEBiology
Trial Class

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

Enzyme Denaturation 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 focus on what happens to enzymes when conditions change, including the effects of extreme temperature and pH on enzyme activity.

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 3/5

    Explain why enzyme activity increases as temperature rises from 20°C to 37°C, but decreases rapidly above 45°C.

    Show model answer and marking guidance
    1. 20–37°C: increasing temperature gives molecules more kinetic energy.
    2. More frequent collisions between enzyme and substrate.
    3. Above 45°C: the enzyme begins to denature.
    4. The active site changes shape and the substrate can no longer fit: reaction rate drops.

    Watch for: Saying the enzyme "dies" at high temperature: enzymes are not alive, they denature.

  2. Question 2

    Paper 4 Both 3 marks Difficulty 3/5

    Define the term "optimum temperature" for an enzyme and state the approximate optimum for most human enzymes.

    Show model answer and marking guidance
    1. The temperature at which the enzyme works fastest / maximum rate of reaction.
    2. For most human enzymes this is approximately 37°C.
    3. This matches normal human body temperature.

  3. Question 3

    Paper 4 Extended 3 marks Difficulty 4/5

    Explain why denaturation is generally irreversible.

    Show model answer and marking guidance
    1. Denaturation changes the 3D shape / tertiary structure of the protein.
    2. Bonds holding the shape are broken permanently.
    3. The active site cannot return to its original shape: the substrate can no longer bind.

  4. Question 4

    Paper 4 Both 3 marks Difficulty 3/5

    Pepsin works best at pH 2 (in the stomach) while trypsin works best at pH 8 (in the small intestine). Explain why pepsin would not work efficiently in the small intestine.

    Show model answer and marking guidance
    1. The pH in the small intestine is alkaline (pH 8), far from pepsin's optimum (pH 2).
    2. At pH 8, pepsin would be denatured.
    3. The active site shape changes so the substrate cannot bind effectively.

  5. Question 5

    Paper 2 Core 2 marks Difficulty 2/5

    State what is meant by "denaturation" of an enzyme.

    Show model answer and marking guidance
    1. The permanent change in shape of the active site.
    2. Caused by high temperature or extreme pH: the enzyme can no longer catalyse the reaction.

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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