California State University, Fullerton

BIOL 191B

HOMEWORK
Answer the following questions on a separate sheet of paper. Be sure to explain your answers and
answer ALL parts of the question. Turn in your answers at the start of the next lab period.
1. Which sample showed a greater rate of lipid digestion, the sample with bile salts or
without bile salts? Explain how you know and how this relates to enzyme activity.
The sample with bile salts showed a greater rate of lipid digestion. The bile salt in this
sample helped break down lipids in milk which increased the surface area showed by the
action of lipases, therefore lipase chemically broke down the lipids which led to a pH
change (low) that changed the color change of the solution to a yellow color and this
occurred because phenol red is an indicator that changes the color of solution as acidity
increases. This indicates that lipid digestion rates increase, and digestion occurred. In
comparison, the color of the solution without bile salts slightly changed which indicates
that the lipids in the milk weren’t completely broken down since there is a low surface
area exposed by the action of lipases to help increase lipid digestion. This is related to
enzyme activity as lipase aid in the digestion of lipids by lowering the energy required to
break down lipids in order for them to be absorbed into the body.
2. Which pH (2 or 8) should show the greater rate of protein digestion for pepsin and
trypsin? Explain your reasoning.
The trypsin pH 8 and pepsin pH 2 both should show an outcome of protein digestion, but
trypsin should show a greater and quicker rate of protein digestion. pH affects the
outcome and function of both enzymes. As Pepsin functions better when pH is acidic (pH
2) and trypsin functions better when pH is basic (pH 8). Therefore, if pH is too basic,
pepsin doesn’t function and if pH is too acidic, trypsin doesn’t function. Trypsin is
produced by the pancreas, and it functions in the small intestine and its pH is basic.
While pepsin is produced by the gastric chief cells in the stomach, and it functions in the
stomach where pH is acidic. Pepsin is a principal enzyme that help break down proteins
into small pieces to be easily absorbed in the small intestine which would make it easier
for trypsin with a pH 8 to digest those small pieces more efficiently at a quicker rate.