Advanced Placement (AP) Biology Practice Exam

What effect does cooling a reaction have on enzymatic activity?

1. It typically speeds up the reaction rate.

2. It has no impact on the reaction.

3. It slows down the reaction rate.

4. It permanently deactivates the enzyme.

The correct answer is: It slows down the reaction rate.

Cooling a reaction generally slows down the reaction rate due to the decrease in kinetic energy among the reacting molecules. Enzymes, which are biological catalysts, rely on molecular motion to facilitate the formation of enzyme-substrate complexes. At lower temperatures, molecules move more slowly, which results in fewer collisions between enzymes and substrates. This decreased likelihood of collisions leads to a reduction in the overall rate of the reaction. It's important to understand that while cooling does not permanently deactivate the enzyme or alter its structure, it can significantly reduce its activity temporarily by influencing the dynamics of the molecular interactions. As the temperature drops, the molecular vibrations and movements necessary for enzyme function diminish, which is why enzymatic reactions are generally most active within an optimal temperature range. Beyond this optimal range, cooling the reaction can lead to a noticeable decrease in reaction speed.