Final answer:
Enzymes are the organic catalysts required in the body for chemical reactions, and they function by lowering the activation energy of reactions.
Step-by-step explanation:
Organic catalysts in the body that are necessary for chemical reactions are called enzymes. These biological catalysts are crucial because they accelerate biochemical reactions by lowering the activation energy, which is essential as most of these reactions would occur too slowly at normal temperatures to sustain life. Enzymes are typically made up of protein molecules and operate by binding to the reactant molecules, or substrates, facilitating the necessary chemical transformations. It is important to understand that while they speed up reactions, enzymes do not alter the overall free energy change of the reaction; they merely make it easier for the reaction to get started by lowering the energy barrier.