OCR GCSE Biology 2026 – 400 Free Practice Questions to Pass the Exam

When an enzyme operates at its optimum temperature, it is indeed functioning at its highest efficiency. This is because the structure of the enzyme is finely tuned to work best at a specific temperature that enhances its kinetic activity. At this optimum level, the enzyme and substrate molecules collide more frequently, leading to a higher rate of product formation and overall reaction speed.

As temperature increases towards the optimum, the kinetic energy of molecules rises, making them move faster and collide more often, facilitating the catalytic process. However, if the temperature exceeds this optimum, it can lead to denaturation, where the enzyme's structure becomes altered and loses its catalytic ability. This is not the case at the optimum temperature where the enzyme is stable and effective.

The other options describe scenarios that are not characteristic of an enzyme operating at its optimal temperature. For example, the reaction occurring at the slowest rate or ceasing entirely would indicate that the enzyme is not functioning optimally, and denaturation suggests a breakdown rather than efficiency.