Answer:
The enzyme activity decreases due to the denaturation of the enzymes.
Step-by-step explanation:
Enzymes are built with proteins. Enzymes catalyze a reaction by binding to the substrate molecule in its active site. As temperature increases the rate of the enzyme activity increases because kinetic energy of the molecules get increases.
But when the temperature crosses approximately 37-40 degrees Celsius the structure of enzyme denatures due to breakage of its intra- and intermolecular bonds. The active parts of an enzyme changes and it can no longer bind to its substrate hence the enzyme activity decreases.