Which biological process best describes the action of enzymes being inhibited by the presence of a competitive inhibitor?

The action of enzymes being inhibited by a competitive inhibitor is best characterized by decreased enzymatic activity. Competitive inhibition occurs when a molecule, the competitive inhibitor, closely resembles the substrate's structure and competes for binding at the enzyme's active site. When the competitive inhibitor occupies the active site, it prevents the actual substrate from binding, leading to a reduction in the rate of the enzymatic reaction.

In this scenario, while the substrate is still present, its ability to bind and react is hindered by the presence of the inhibitor. Thus, the overall enzymatic activity diminishes because fewer enzyme-substrate complexes can form, resulting in a lower output of the product. This highlights the direct impact a competitive inhibitor has on enzyme functionality, making decreased enzymatic activity the correct choice for describing this biological process.