In an enzyme-catalyzed reaction, substrates are the molecules that undergo chemical change.

• A. True (correct)
• B. False
• C. The solvent
• D. The products

Answer: (A)

Substrates are the molecules that actually undergo chemical change in an enzyme-catalyzed reaction. The enzyme binds the substrate at its active site, forming an enzyme–substrate complex, and helps transform the substrate into products by lowering the activation energy. After the reaction, the products are released and the enzyme is free to catalyze more conversions. The solvent is just the medium in which the reaction occurs, not the molecule that changes, and the products are the new molecules formed. So this statement is correct.