Answer:
Reactant
Explanation:
The substances that are inserted first into a chemical reaction are the reactants. They are at the beginning of the reaction and it is these substances that will react and undergo transformation.
The products, on the other hand, are the resulting substances of the chemical reaction that occurs between two or more reagents.
Catalyst is a chemical substance that does not participate in the chemical reaction (like reactants and products). Its role is to decrease the activation energy and increase the speed of reactions.
Enzymes are organic substances (proteins) that act as catalysts in various metabolic processes of living things.