Answer:
The reactant in a chemical reaction upon which an enzyme acts is called the substrate.
Step-by-step explanation:
Enzymes are biological catalysts that facilitate chemical reactions by lowering the activation energy required for the reaction to occur. They do this by binding to specific substrates and converting them into products.
Enzymes have a specific three-dimensional structure that allows them to bind with their substrates at a region called the active site. The substrate fits into the active site like a lock and key, and the enzyme-substrate complex is formed. Within this complex, the enzyme catalyzes the conversion of the substrate into the desired product(s). Once the reaction is complete, the products are released, and the enzyme is free to bind to another substrate molecule and catalyze the reaction again.