OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

How do enzymes affect the activation energy of a reaction?

1. They increase the activation energy

2. They have no effect on activation energy

3. They decrease the activation energy

4. They can block activation energy

The correct answer is: They decrease the activation energy

Enzymes are biological catalysts that facilitate chemical reactions in living organisms by lowering the activation energy required for those reactions to occur. Activation energy is the minimum amount of energy needed for a chemical reaction to take place. When enzymes bind to their substrates (the molecules upon which enzymes act), they form an enzyme-substrate complex. This complex stabilizes the transition state, which is the temporary state during a reaction when substrates are transformed into products. By stabilizing this transition state and providing an alternative reaction pathway, enzymes reduce the amount of energy needed to initiate the reaction. This reduction in activation energy means that reactions can occur more easily and more quickly, which is crucial for the functioning of biological systems. By promoting more efficient reactions, enzymes play an essential role in metabolism and various physiological processes.