1. The correct answer is pH.
The activity of the enzymes might be affected by environmental changes such as change in pH. Each enzyme has the point when it is the most active and this value is known as the optimum pH. Extremely high or low pH values can lead to loss of enzyme activity and stability.
Phosphofructokinase is sensitive to acidity, meaning that it is inhibited by low pH levels.
2. The correct answer is temperature.
Enzyme is sensitive to the environmental conditions such as temperature changes.
Temperature is a factor that usually increases the rate of enzyme-catalyzed reactions by increasing the activity of enzymes. But, after reaching the optimum temperature, reaction rate abruptly declines. This happens because enzymes are deactivated or denatured at a certain temperature (above 40° C).
D. Myosin and actin do not fully detach, so the muscle cannot relax.
