Which statement about enzymes is true? An enzyme functions to increase the rate of a chemical reaction. Enzymes are proteins that function as catalysts in nonliving things. Each enzyme can catalyze many different biochemical reactions ... Enzymes and substrates fit together like a lock and key.

The correct answer is Enzymes and substrates fit together like a lock and key. Enzymes are biological catalysts which increase the reaction rate by lowering its activation energy and convert substrates into products. There is a model which describes fiting in geometrical shape of the enzyme and his substrate. This model is called "Lock and key" model.