2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH

If the pH is too far from the ideal, optimum pH, the enzymes can de-nature, as a change in pH can cause the bonds that hold the structure in place to break :( This would mean that the substrate no longer fits in the active site. 

Different enzymes will work at different pH values. Eg the enzymes in your stomach will work best at a more acidic pH than those in your small intestine.

Figure 1: A graph showing the relationship between rate of enzyme activity
and pH