What role do enzymes play in biological reactions?

Enzymes are biological catalysts that significantly increase the rate of chemical reactions by lowering the activation energy required for reactions to occur. Activation energy is the minimum amount of energy that reactants must possess for a successful chemical reaction to take place. By providing an alternative reaction pathway with a lower activation energy, enzymes make it easier for the reactants to collide in a way that leads to product formation.

This property of enzymes is crucial in biological systems, as many reactions that are vital for life would occur too slowly without the assistance of enzymes. The lower activation energy not only speeds up the reaction but also allows it to proceed under the mild conditions found in living organisms, such as physiological temperature and pH.

In contrast, the other options do not accurately describe the role of enzymes. Enzymes do not slow down reactions, nor do they act as substrates or change the nature of reactants themselves. Instead, they facilitate the transformation of substrates into products by providing a suitable environment for the reaction to occur.