What role do enzymes play in the body?

• A. They make up fibers that join together and offer support for body parts.
• B. They transport nutrients in the bloodstream.
• C. They control chemical reactions inside the cells.
• D. They prevent foreign bodies from entering the cells.

Answer: (C)

Enzymes act as biological catalysts, accelerating chemical reactions inside cells. They work by binding to specific substrates at their active sites and lowering the activation energy needed for the reaction to occur, so metabolic processes run quickly at normal body conditions. This makes them essential for virtually all cellular functions, from digestion to energy production. Enzymes are usually proteins (with some RNA enzymes), highly substrate-specific, and their activity can be influenced by temperature, pH, and inhibitors. They are not structural fibers that provide support, not transporters moving nutrients through the bloodstream, and not barriers against foreign invaders—that role belongs to membranes and the immune system. In short, enzymes control chemical reactions inside the cells.