Which statement best describes enzyme activity with temperature change?

• A. It increases up to the optimum temperature, then decreases due to denaturation
• B. It decreases as temperature increases
• C. It remains constant with temperature
• D. It increases indefinitely

Answer: (A)

Enzyme activity depends on temperature because heat increases the kinetic energy of molecules, making collisions between enzyme and substrate more frequent and effective up to a point. As temperature rises from very low levels, the rate of catalysis typically increases. But enzymes have a shape maintained by weak bonds; when temperature gets too high, those bonds break and the enzyme unfolds or its active site changes shape. This denaturation reduces or abolishes the enzyme’s ability to catalyze reactions. So there is an optimal temperature where activity is highest, with lower activity both below and above that point. The idea that activity would keep increasing or stay constant with temperature doesn’t fit how enzyme structure depends on temperature, and the notion of unlimited increase ignores denaturation.