Final answer:
The true statement about enzyme-catalyzed reactions is that the rate of product formation changes in direct proportion to enzyme concentration until reaching a saturation point. Other factors such as temperature and pH also critically influence the rate of these reactions.
Step-by-step explanation:
The correct statement about enzyme-catalyzed reactions is: Under given conditions of substrate concentration, pH, and temperature, the rate of product formation varies directly with enzyme concentration up to a maximum, at which point the rate cannot be increased further.
Enzyme activity is influenced by several factors including temperature, pH, and substrate concentration. Increases in enzyme concentration typically lead to increases in reaction rates, assuming the substrate is in excess. However, with all other factors constant, if the enzyme becomes saturated with substrate, further increases in substrate concentration do not significantly increase the rate of reaction.
Temperature is another crucial factor, with reaction rates increasing as the temperature rises until an optimum level. Beyond this, enzymes can become denatured and cease to function efficiently. Each enzyme has an optimum pH at which it functions best, and a shift away from this pH can decrease the enzyme’s activity.