Final answer:
An enzyme affects a reaction by lowering the activation energy required for the reaction to occur.
Step-by-step explanation:
An enzyme affects a reaction by lowering the activation energy required for the reaction to occur. Activation energy is the energy needed to initiate a chemical reaction. Enzymes act as catalysts, meaning they speed up the rate of a reaction by providing an alternative pathway with a lower activation energy. This allows the reaction to occur more quickly and efficiently.
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