Activation energy is

• A. Decreased by enzymes
• B. The energy needed for an enzyme reaction to stop
• C. Increased by enzymes
• D. Very high in catalyzed reactions

Answer: (A)

Activation energy is the energy barrier that must be overcome for a reaction to proceed. Enzymes lower this barrier by providing an alternative, lower-energy pathway—stabilizing the transition state and aligning substrates precisely in the active site. This reduction in activation energy speeds up the reaction without changing the overall energy difference between reactants and products. So, activation energy is decreased by enzymes. The idea that enzymes increase activation energy, or that it’s energy needed to stop the reaction, or that it’s very high in catalyzed reactions, does not fit the way enzymes function.