Explain why increasing the temperature from 10 °C to the optimum temperature increases the rate of an enzyme-controlled reaction, and what happens to the rate of reaction when the temperature is raised well above the optimum.

Cambridge International IGCSE Biology (0610) — 5.1 Enzymes · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Increasing temperature raises the kinetic energy of molecules, so enzyme and substrate collide more often and more successfully.
This increases the number of enzyme–substrate complexes and therefore the rate of reaction.
When the temperature is raised well above the optimum the enzyme becomes denatured.
Denaturation permanently alters the shape of the active site, preventing substrate binding and the rate of reaction falls.

Examiner tips

  • Use the term ‘kinetic energy’ and ‘enzyme–substrate complexes’. Explain the two effects: increased collisions and denaturation. Show the change in rate (increase then decrease).

Common mistakes

  • Confusing ‘denaturation’ with ‘inactivation’. Forgetting to mention the loss of active‑site shape. Using vague terms like ‘more energy’ without linking to collisions.

Mark scheme (4 marks)

  1. Increasing temperature increases the kinetic energy of molecules
  2. More frequent / successful collisions between enzyme and substrate, so more enzyme-substrate complexes form
  3. Above the optimum temperature the enzyme becomes denatured
  4. Denaturation causes a permanent change in the shape of the active site, so the substrate can no longer bind and the rate of reaction decreases

Key terms in this question

optimum temperature · rate of reaction

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