A scientist observes that, when the pH of the environment surrounding an enzyme is changed, the rate the enzyme catalyzes a reaction greatly decreases. Which statement best describes how a change in pH can affect an enzyme?

A. A pH change can cause the enzyme to change its shape.

B. A pH change can remove energy necessary to activate an enzyme.

C. A pH change can add new molecules to the structure of the enzyme.

D. A pH change can cause an enzyme to react with a different substrate.

A - A pH change can cause the enzyme to change its shape

Explanation:

A rise or fall in the pH of the medium from the optimum of pH 7 usually affect the enzymes' active sites of and therefore the shape and the rate of enzyme activity.

Assuming the pH is too low, the enzyme medium becomes acidic; Acidosis. The high Hydrogen ions concentration interacts with the R-groups of the amino acids moiety of the enzymes, this interaction affects the ionization of the R-groups, disrupting the ionic bonding holding these R-groups in shape.

This results in loss of the 3-Dimensional shape arrangements of the protein molecule and therefore of the active sites. Since active sites of enzymes determines the specificity of the enzymes substrate - complex to give enzyme-product complex, the catalytic activity of the enzymes decreases, the rate of reaction decreases, and products formation stops, and the reaction also stops.

The same is applicable to extremely high pH=Alkalosis.

However, the effective buffer system of the body prevents this scenarios from happening in real sense in the body. Through mopping by the haemoglobin, excretion by the kidney, etc