What is the main function of enzymes in living organisms?

Enzymes play a crucial role in biological reactions by acting as catalysts, which means they accelerate the rates of these reactions without being consumed in the process. This is essential for many metabolic pathways, as most biochemical reactions would occur too slowly for life to sustain itself without enzymatic assistance. By lowering the activation energy needed for reactions, enzymes allow processes such as digestion, respiration, and cellular metabolism to occur efficiently at the temperatures found in living organisms.

While storing energy, providing structure, and transporting molecules are functions carried out by other types of biological molecules (like carbohydrates, proteins, and lipids), these are not the primary roles of enzymes. Enzymes are specifically designed to facilitate biochemical reactions, making option B the correct choice for the main function of enzymes in living organisms.