why the enzyme function varies with substrate concentration before the catalase concentration was saturated with hydrogen peroxide.

The rate of enzyme reaction increases with increase in substrate concentration. Upon saturation of active site of the enzyme with the substrate, there will be no effect on the rate of reaction.

Explanation:

Enzymes are protein molecules secreted by special cells in a living organism. They are organic catalysts responsible for the metabolic reactions that take place in living organisms. Thus, glycolysis, synthesis of proteins and photosynthesis are mediated by numerous enzymes.

Also, enzymes may be classified according to the type of reaction they catalyze. They include: oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, and translocases.

From the question, catalase enzyme is a type of oxidoreductase enzyme that catalyzes the decomposition of hydrogen peroxide (substrate) into water and molecular oxygen.

The regions on the enzyme into which the substrate molecules fit are known as the ACTIVE SITES of the enzyme.

Substrate concentration is one of the factors that affect enzyme rate of reaction. The enzyme function varies with substrate concentration because the rate of enzyme reaction increases with increase in substrate concentration. Upon saturation of ACTIVE SITE of the enzyme with the substrate, there will be no effect on the rate of reaction.