Here is an example of the kind of material presented in an MCAT passage that would lead to excellent multiple choice questions. Plots of catalytic rate versus pH can be used to determine which ionizable groups are participating in catalysis. When the rate undergoes a large alteration over a small pH range, it is a plausible though not definitive supposition those amino acid residues whose side chains with pKa's in that range are playing an important roll in catalysis.