A Level Biology Practice Exam

Which factor does NOT typically affect enzyme activity?

1. Substrate concentration

2. Enzyme concentration

3. Time of day

4. Temperature

The correct answer is: Time of day

The time of day does not typically influence enzyme activity, unlike factors such as substrate concentration, enzyme concentration, and temperature, which play crucial roles in enzyme function. Substrate concentration impacts enzyme activity significantly because the rate of reaction can increase with more substrate, up to a point where all active sites of the enzyme molecules are occupied (saturation point). Similarly, an increase in enzyme concentration generally leads to a higher reaction rate as long as there is sufficient substrate available. Temperature can affect the kinetic energy of molecules, altering reaction rates; most enzymes have an optimal temperature range where they function best before denaturing at higher temperatures. In contrast, while some enzymes may be influenced by circadian rhythms or hormonal signals related to the time of day, this is not a universal factor affecting enzyme activity across all enzymes. Therefore, it stands out as the factor that does not typically affect enzyme activity in a straightforward manner.