The effect of pH on enzyme activity is critical, as enzymes function optimally within specific pH ranges. Deviations from these ranges can lead to decreased enzyme activity or denaturation. For instance, in humans, the enzyme pepsin works best in the acidic environment of the stomach, while others like trypsin are active in alkaline conditions of the small intestine. The relationship between pH and enzyme activity emphasizes the importance of maintaining homeostasis for proper metabolic functioning.