Question

practice it
the function of an enzyme is to

increase the activation energy of a chemical reaction.
speed up the rate of a chemical reaction.
change the direction of a chemical reaction.
prevent a chemical reaction from occurring.
stop a chemical reaction once it has started.

Explanation:

Enzymes are biological catalysts. Catalysts lower the activation - energy of a chemical reaction, which in turn speeds up the rate of the reaction without changing the reaction's direction, preventing it, or stopping it once it has started.

Answer:

speed up the rate of a chemical reaction.