Final answer:
Enzymatic reactions reach saturation when all enzyme active sites become filled, making enzyme molecules unable to bind more substrate and causing the reaction rate to plateau.
Step-by-step explanation:
Enzymatic reactions can become saturated as substrate concentration increases because active sites become filled. This occurs when all available enzyme molecules have their active sites occupied by substrate molecules, leading to a plateau in the reaction rate regardless of any further increase in substrate concentration. The enzyme-substrate complex can only form at available active sites; when these are all occupied, the addition of more substrate will not increase the rate of reaction any further.
At low temperatures, increasing the temperature increases the rate of an enzyme-catalyzed reaction; however, enzyme activity decreases at higher temperatures as they begin to denature, losing their structural integrity and functionality. With respect to pH, enzymes have an optimum range where they perform most effectively; pH levels outside of this range can also result in enzyme denaturation.