Here's why:

* pH: Enzymes have an optimal pH range where they function best. Changes in pH can disrupt the enzyme's structure, particularly the active site, which is responsible for binding to the substrate. This disruption can lead to a decrease in enzyme activity or even denaturation (loss of function).

* Temperature: Enzymes are proteins, and like all proteins, they have a specific temperature range where they work optimally. At low temperatures, enzyme activity slows down. As temperature increases, enzyme activity generally increases until it reaches an optimal point. Beyond this optimal temperature, the enzyme begins to denature, causing a loss of function.

Let me know if you'd like more details about how pH and temperature affect enzyme function!