Describe how temperature affects the rate of an enzyme-controlled reaction, including what happens both below and above the enzyme's optimum temperature.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
As temperature rises, the kinetic energy of molecules increases, so collisions between enzyme and substrate become more frequent and more likely to be successful, leading to a higher rate of reaction. The rate continues to rise until the optimum temperature is reached, at which point the reaction rate is at its maximum.
Beyond the optimum temperature the enzyme begins to denature; the active site changes shape and loses its specific fit for the substrate. Consequently, enzyme‑substrate complexes can no longer form efficiently, and the reaction rate falls sharply.
Beyond the optimum temperature the enzyme begins to denature; the active site changes shape and loses its specific fit for the substrate. Consequently, enzyme‑substrate complexes can no longer form efficiently, and the reaction rate falls sharply.
Examiner tips
- Use the phrase "optimum temperature" and state that the rate is maximum there.
- Explain the kinetic energy/collision effect for the rise in rate.
- Mention denaturation and loss of active‑site shape for the fall in rate.
- Keep the answer concise and use the exact terminology from the mark scheme.
Common mistakes
- Confusing the effect of temperature with pH changes.
- Saying the rate simply "decreases" without mentioning denaturation.
- Using vague terms like "hot" or "cold" instead of "below/above optimum".
Mark scheme (5 marks)
- As temperature increases up to the optimum, the rate of reaction increases
- Because molecules have more kinetic energy and move faster, leading to more successful collisions / more enzyme-substrate complexes forming
- At the optimum temperature the rate of reaction is at its maximum / fastest
- Above the optimum temperature the enzyme becomes denatured / the active site changes shape
- Denaturation means the substrate can no longer fit into the active site, so no enzyme-substrate complexes form and the rate of reaction decreases
Key terms in this question
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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