For an enzyme to work, it must:
1. Collide with its substrate.
2. Have an active site which fits the substrate
All factors that affect the rate of enzymes, will affect one or both of the above.
You need to know about the effects of temperature and pH
Explaining the Temperature Graph
An initial rising curve
Peak at optimum temperature = 37oC
A sharp decreasing curve
Enzymes are proteins and their functioning is dependent on their shape, particularly the shape of the active site.
When temperature is increased beyond the optimum, bonds within the enzyme start to break. The active site changes shape and the substrate can no longer fit. The enzyme is denatured. This is irreversible.