AQA GCSE Biology Paper 1 Practice Exam 2026 – Complete Study Guide

Enzymes in plants, like all enzymes, have optimal temperature ranges within which they function best. At low temperatures, the kinetic energy of the molecules decreases, which leads to slower movement. This reduced movement lowers the frequency of collisions between enzymes and substrate molecules, resulting in significantly slowed enzymatic reactions. Therefore, at lower temperatures, enzymes are less active, leading to decreased rates of metabolic processes and other physiological functions in plants.

In contrast, high temperatures can lead to increased enzyme activity up to a certain point, after which denaturation may occur. Excess light might enhance photosynthesis but doesn't directly correlate with enzyme efficiency in a detrimental way, while low carbon dioxide can limit photosynthesis rates but does not solely affect enzyme activity at the level that low temperature does. Thus, low temperature is the primary condition that causes enzymes to work very slowly in plants.