Which of the following factors can lead to decreased enzyme activity when the temperature is too low?

When temperature is low, molecular movement, including that of both enzymes and substrates, decreases significantly. Enzymes operate most efficiently within a specific temperature range, typically around their optimal temperature. Lower temperatures result in less kinetic energy, which ultimately leads to fewer effective collisions between enzymes and substrates. This reduced interaction decreases the likelihood of the formation of enzyme-substrate complexes, thus diminishing overall enzyme activity.

In contrast, increased substrate collisions, optimal energy levels, and increased enzyme concentration are more likely to enhance enzyme activity rather than impair it. Hence, decreased molecular movement directly correlates with reduced enzyme activity in low-temperature scenarios, making it the correct choice.