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 enzyme and substrate collide more often and more successfully, forming more enzyme–substrate complexes and the reaction rate rises until the optimum temperature is reached.
Below the optimum the reaction rate continues to increase with temperature because collisions are more frequent.
Above the optimum the enzyme becomes denatured; the active site changes shape and the substrate can no longer fit, so the number of enzyme–substrate complexes falls and the reaction rate decreases.
Below the optimum the reaction rate continues to increase with temperature because collisions are more frequent.
Above the optimum the enzyme becomes denatured; the active site changes shape and the substrate can no longer fit, so the number of enzyme–substrate complexes falls and the reaction rate decreases.
Examiner tips
- Use the phrase ‘optimum temperature’ and explain the two temperature ranges (below/above).
- Show the link between kinetic energy, collision frequency and complex formation.
- Mention denaturation and loss of active‑site shape for the high‑temperature drop.
- Use the word ‘denatured’ – examiners look for this term.
Common mistakes
- Failing to mention the enzyme becoming denatured above optimum.
- Using vague terms like ‘too hot’ instead of ‘denaturation’.
- Not distinguishing the two temperature ranges (below and above optimum).
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, leading to more successful collisions between enzyme and substrate
- More enzyme-substrate complexes form (at or below the optimum)
- Above the optimum temperature, the enzyme becomes denatured / the active site changes shape
- The substrate can no longer fit into the active site, so the rate of reaction decreases
Key terms in this question
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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