Explain why an increase in temperature from 10°C to the optimum temperature increases the rate of an enzyme-controlled reaction, and what happens to the enzyme if the temperature is increased well above the optimum.

WJEC A-Level Biology (Wales) — 1.1 Chemical elements and biological molecules · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Increasing temperature gives molecules more kinetic energy, so they move faster and collide more often. This increases the number of successful enzyme–substrate collisions, forming more enzyme–substrate complexes and raising the reaction rate. If the temperature is increased well above the optimum, the enzyme becomes denatured. Denaturation permanently changes the shape of the active site, preventing substrate binding and stopping the formation of enzyme–substrate complexes.

Examiner tips

  • Use the term "kinetic energy" and "successful collisions" to show understanding of the rate increase.
  • Mention "denatured" and "permanent change in the active site" for the high‑temperature effect.
  • Keep the answer concise – 5 marks can be achieved with two short paragraphs.
  • Use UK spelling (e.g. "enzymatic").

Common mistakes

  • Confusing increased temperature with increased concentration; only temperature affects kinetic energy. Saying the enzyme is "inactivated" without explaining denaturation. Using vague terms like "more activity" without linking to collisions or active‑site shape.

Mark scheme (5 marks)

  1. Increasing temperature gives molecules more kinetic energy
  2. Molecules move faster, so more successful collisions occur between enzyme and substrate
  3. More enzyme-substrate complexes form, increasing the rate of reaction
  4. At temperatures well above the optimum, the enzyme becomes denatured
  5. Denaturation causes a permanent change in the shape of the active site, so the substrate can no longer fit and no enzyme-substrate complexes can form

Key terms in this question

optimum temperature

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