a) A single type of enzyme could not be used in every region of the body because the body is not a single celled organism, it is a multicellular organism and each cell needs special and specific care in order to function.
A single type of enzyme could not control all the different systems of the body. Different enzymes and specialized cells have the responsibility to carry out specific functions so that the body can properly operate. One type of enzyme could not manage the excretory, digestive, reproductive, skeletal systems etc as these regions of the body require distinct attention and assistance to keep the body regulations active and to maintain proper health.
b) Problems expected of someone who lacks pepsin would be a protein deficiency. This would be present by way of weak and brittle bones and overall immuno compromised health.
Another problem expected would be stunted growth and development. As an individual is not receiving the right and recommended amount of digested protein, their bodies will lack the nutrients to properly grow as they age.