A student investigates the effect of temperature on the activity of amylase. As the temperature is increased from 10°C to 40°C, the rate at which amylase breaks down starch increases. Above 40°C, the rate of reaction decreases until amylase no longer functions. Explain these observations.

WJEC A-Level Biology (Wales) — 1.2 Cell structure and organisation · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Between 10°C and 40°C, the kinetic energy of the molecules increases, so more collisions occur between amylase and starch. The increased frequency of successful collisions leads to more enzyme‑substrate complexes, raising the rate of reaction. Above 40°C the high temperature changes the shape of the amylase active site – the enzyme is denatured. The altered active site can no longer bind starch, so enzyme‑substrate complexes cannot form and the reaction stops.

Examiner tips

  • Use the term ‘kinetic energy’ and ‘successful collisions’ to show understanding of temperature effects.
  • Explain that denaturation changes the active site shape, preventing substrate binding.
  • Keep the answer concise – 5 points, one sentence per point.
  • Use UK spelling (e.g. ‘enzyme’).

Common mistakes

  • Confusing increased temperature with increased enzyme concentration.
  • Saying the enzyme is ‘inactive’ instead of ‘denatured’ and not mentioning the loss of substrate binding.

Mark scheme (5 marks)

  1. Between 10°C and 40°C, molecules have more kinetic energy as temperature increases
  2. More successful collisions occur between the substrate and the active site of the enzyme
  3. More enzyme-substrate complexes form, so the rate of reaction increases
  4. Above 40°C, the active site of the amylase changes shape / the enzyme is denatured
  5. The substrate can no longer fit into the active site, so no enzyme-substrate complexes can form and the reaction stops

Key terms in this question

amylase

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