WJEC Biology Practice Exam

Enzymes function as biological catalysts primarily by lowering the activation energy required for chemical reactions to occur. This reduction in activation energy means that reactions can proceed more quickly and efficiently, making it possible for biological processes to happen at temperatures and conditions compatible with life.

Enzymes achieve this by binding to the substrates— the reactants in a reaction— and stabilizing the transition state. This allows the reaction to occur at a much lower energy level than would otherwise be needed. By facilitating this process, enzymes enable organisms to carry out vital biochemical reactions, such as digestion, metabolism, and DNA replication, at a rate that supports life.

The other options involve misconceptions about how enzymes work. Enzymes do not increase the temperature of reactions, nor do they alter pH specifically to catalyze reactions, even though temperature and pH can affect enzyme activity. They also do not provide energy to reactions; rather, they make it easier for the existing energy in substrates to be utilized more efficiently. This key characteristic of enzymes as catalysts underpins much of biochemistry and allows for the complex reactions necessary for life to occur seamlessly.