Final answer:
Enzymes are proteins that act as biological catalysts, regulating the rate of chemical reactions in living things without being altered themselves.
Step-by-step explanation:
Enzyme
An enzyme is a protein that acts as a biological catalyst. Enzymes are substances that regulate the rate of chemical reactions without being changed in the process. They speed up reactions by reducing the amount of activation energy needed to start the reaction. For example, salivary amylase is an enzyme that hydrolyzes its substrate amylose, a component of starch.