Question

they want to use their knowledge to determine the action of the enzyme pepsin when digested in the human stomach. they know that gastric juice in the stomach contains water, pepsin, and hydrochloric acid (hcl). they decide to use egg - white and pieces of cooked egg - white as the protein to be digested.
they set up four test tubes and place equal, small amounts of egg - white in each test tube. then they fill each test tube with a different liquid to a height of 3 cm. in test tube 1 they add water, in test tube 2 they add dilute hcl (hcl), in test tube 3 they add pepsin in water, and in test tube 4 they add pepsin and dilute hydrochloric acid. they place the four test tubes in an incubator at 37°c (body temperature).
after one day, they observe the results. they return the test tubes to the incubator and observe them again the next day. the table below is a record of the results.
protein digestion data table

test tube	1 day	2 days
2. egg + hcl	no change	no change
3. egg + pepsin	liquid slightly cloudy, egg - white solid	liquid cloudy, egg - white still solid
4. egg + pepsin + hcl	liquid cloudy, pieces of egg smaller	liquid very cloudy, almost no egg remains

what is the best conclusion for this experiment, considering the role of ph in enzyme activity? (5pts)
a. water is the most effective liquid for protein digestion in the stomach, as it maintains a neutral ph.
b. hcl alone is sufficient to digest protein in the stomach because it lowers the ph to an optimal level for protein digestion.
c. both pepsin and hcl are necessary for the effective digestion of protein in the stomach because hcl lowers the ph to an optimal level for pepsin activity.
d. pepsin alone is sufficient to digest protein in the stomach as it can function effectively without any change in ph.

Explanation:

Pepsin is an enzyme that digests proteins, and its activity is highly dependent on pH. Hydrochloric acid (HCl) in the stomach creates an acidic environment which is optimal for pepsin activity. In the experiment, when only water or only HCl was added to egg - white (protein), there was no digestion. When only pepsin was added, digestion was minimal. But when both pepsin and HCl were added, significant protein digestion occurred. This shows that both pepsin and HCl are necessary for effective protein digestion in the stomach as HCl lowers the pH to an optimal level for pepsin activity.

Answer:

C. Both pepsin and HCl are necessary for the effective digestion of protein in the stomach because HCl lowers the pH to an optimal level for pepsin activity.