A Levels Biology (9700)•9700/12/M/J/21
Explanation
Enzyme Lowers Activation Energy Barrier
Steps:
- Activation energy (Ea) is the energy difference from substrates to transition state.
- Uncatalyzed reaction has higher Ea; enzyme-catalyzed has lower Ea.
- Graph shows energy profiles for both paths, with transition state peaks.
- Reduction in Ea is the vertical distance between the two peaks.
Why B is correct:
- B points to the difference between uncatalyzed and catalyzed Ea peaks, matching the definition of enzyme-induced lowering of the activation energy barrier.
Why the others are wrong:
- A shows uncatalyzed Ea height, not the reduction.
- C shows catalyzed Ea height, not the difference.
- D indicates overall energy change (ΔG), unrelated to activation energy.
Final answer: B
Topic: Mode of action of enzymes
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