Activation energy can be reduced by the presence of?

Activation energy is the minimum amount of energy required for a chemical reaction to occur. The presence of a catalyst plays a crucial role in reducing this activation energy, thereby increasing the rate of the reaction. Catalysts provide an alternative pathway for the reaction to take place, which has a lower energy barrier than the uncatalyzed reaction.

Enzymes are a specific type of catalyst that facilitate biochemical reactions in living organisms. They work by binding to substrates and stabilizing the transition state, which effectively lowers the activation energy needed for the reaction to proceed. While enzymes are technically catalysts, they are often discussed separately in biochemical contexts because of their highly specific nature and regulation.

In contrast, inhibitors typically raise the activation energy or interfere with the reaction process, while substrates are the reactants that enzymes act upon and do not affect the activation energy in the way that catalysts do. Hence, the answer correctly identifies that activation energy can be reduced by a catalyst.