Final answer:
Enzyme activity is primarily affected by environmental temperature, pH levels, and substrate concentration. Deviations from their optimal conditions can lead to enzyme denaturation and altered reaction rates.
Step-by-step explanation:
The three main factors that can affect enzyme activity are temperature, pH levels, and substrate concentration. Enzymes, being proteins, have specific conditions under which they function optimally. Changes in temperature can cause enzymes to lose their three-dimensional structure and function when too high or too low, a process known as denaturation. Similarly, the optimal pH value is crucial for enzyme activity; extreme pH levels can also lead to denaturation. Lastly, the substrate concentration affects the rate of enzyme-catalyzed reactions; an increase in substrate concentration usually leads to an increased reaction rate until the enzyme is saturated.