Question

a substance that influences the reaction but does not participate in the reac catalyst reactant product substrate

Explanation:

A catalyst is a substance that speeds up a chemical reaction without being consumed in the reaction. Reactants are substances that participate in the reaction. Products are the substances formed as a result of the reaction. A substrate is a substance on which an enzyme acts. Since the question describes a substance that influences the reaction but does not participate in it, the catalyst fits this description.

Answer:

A. catalyst