Final answer:
Enzymes are protein-based catalysts in living organisms that speed up biological reactions by lowering the activation energy required.
Step-by-step explanation:
Enzymes are protein molecules that serve as catalysts for certain biological reactions, such as digestion, energy production, and molecular synthesis. By binding to specific reactants known as substrates, enzymes lower the activation energy of chemical reactions inside cells, facilitating processes necessary for life. A well-known example of an enzyme is salivary amylase, which helps in the digestion of starch into simpler sugars.