At a temperature just below the freezing point,the enzyme:

The rate of enzyme reactions rises with the increase in substrate concentration. But it does $NOT$ increase beyond a certain concentration because . . . . . . .

In homeotherms,the enzymatic reaction occurs best at . . . . . . °$C$.

What is the effect of temperature and pH on the activity of an enzyme?

At which temperature do enzymes lose their native conformation?

$A$ - Activity of an enzyme can be affected by a change in environmental conditions.
$R$ - These factors regulate the activity of the enzyme.