Final answer:
Enzymes are protein catalysts that speed up metabolic biological reactions in an organism by lowering the activation energy required for these reactions, hence they are vital for cellular metabolism.
Step-by-step explanation:
Protein catalysts that speed up the various metabolic biological reactions in an organism are called enzymes. An enzyme functions by lowering the activation energy needed for a reaction to occur, thereby allowing the reaction to proceed more quickly than it would without the presence of the enzyme. This is crucial because most biochemical reactions are too slow under regular conditions within cells. For example, salivary amylase is an enzyme that catalyzes the breakdown of starch into sugars in the mouth.
Most enzymes are proteins, but some RNA molecules can also act as enzymes. They are highly specific to their substrates and can be reused for multiple reactions since they are not consumed by the reaction they catalyze. The role of enzymes in cellular metabolism is vital, as they facilitate reactions that are essential for life.