What role does a catalyst play in chemical reactions?

A catalyst plays a crucial role in chemical reactions primarily by increasing the reaction rate. It achieves this by providing an alternative pathway for the reaction to occur, which typically has a lower activation energy compared to the uncatalyzed reaction. As a result, the reactants are able to transform into products more quickly.

One of the distinguishing features of a catalyst is that it is not consumed during the reaction; this means it can be used repeatedly in multiple reaction cycles. Consequently, it can facilitate reactions in both directions without undergoing any permanent change itself. This characteristic makes catalysts invaluable in both biological systems, where enzymes act as biological catalysts, and in industrial processes, where they are used to enhance reaction efficiency and yield.

In this context, the correct answer highlights the catalyst's function of speeding up reactions while remaining unchanged, emphasizing its importance in chemistry and various applications.