In enzyme-catalyzed reactions, what role does an enzyme play?

• A. It provides energy to start the reaction
• B. It lowers the activation energy and accelerates the reaction
• C. It is consumed and becomes part of the product
• D. It remains unchanged but slows down the reaction

Answer: (B)

Enzymes act as biological catalysts by lowering the activation energy required for a reaction to proceed. They achieve this by binding substrates at the active site and stabilizing the transition state, providing an alternative, lower-energy pathway. As a result, the reaction rate increases without the enzyme being consumed or becoming part of the product; enzymes are unchanged after the reaction and can catalyze additional reactions. The other statements don’t fit because enzymes don’t supply energy to start the reaction, they don’t become part of the product, and they don’t slow down the reaction.