Explain 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, molecules gain kinetic energy, move faster and collide more often, so more enzyme‑substrate complexes form and the reaction rate increases up to the optimum temperature.
Below the optimum the rate continues to rise because collisions are more frequent and successful.
Above the optimum the enzyme becomes denatured; the active‑site shape changes permanently, so the substrate can no longer bind. Consequently enzyme‑substrate complexes cannot form and the reaction rate falls.
Below the optimum the rate continues to rise because collisions are more frequent and successful.
Above the optimum the enzyme becomes denatured; the active‑site shape changes permanently, so the substrate can no longer bind. Consequently enzyme‑substrate complexes cannot form and the reaction rate falls.
Examiner tips
- Use the word "optimum" and mention both the rise and fall of the rate.
- Explain the role of kinetic energy and collisions before the optimum.
- Describe denaturation and loss of active‑site shape after the optimum.
- Show the logical link between temperature, enzyme structure and reaction rate.
Common mistakes
- Failing to mention denaturation or the loss of active‑site shape.
- Using vague terms like "hot" or "cold" instead of "below/above optimum".
- Not linking increased collisions to more enzyme‑substrate complexes.
Mark scheme (5 marks)
- As temperature increases up to the optimum, the rate of reaction increases
- Because molecules have more kinetic energy, so move faster and collide more frequently / more successfully
- More enzyme-substrate complexes form (at or below the optimum)
- Above the optimum temperature the enzyme is denatured / the shape of the active site changes permanently
- The substrate can no longer fit into the active site, so no enzyme-substrate complexes can 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 "Explain" question →
- Decode the mark scheme abbreviations →
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