Which enzyme initiates the digestion of proteins?
A. Trypsin
B. Pepsin
C. Aminopeptidase
D. Carboxypeptidase

Hint: Digestion is a complex natural process of breaking down food and minerals into simpler form in order to fuel up the energy production in the body. This process is common to all vertebrates.

Complete Answer
Let's study each of the enzymes mentioned above in order to find the correct answer.
a) Trypsin is an enzyme that is although concerned with digestion of protein yet can't be considered the correct answer for the question because it helps in digestion of protein already acted upon by pepsin secreted in the stomach. Therefore, A is an incorrect option.
b) Pepsin is another enzyme that is secreted in the stomach by specialised cells of the stomach. It is secreted in an inactive form called pepsinogen. This pepsinogen is later acted upon by HCl acid in the stomach, leading to the formation of Pepsin. This pepsin breaks down protein into peptides and amino acids. Therefore, we can say that this enzyme is concerned with initiation of digestion of proteins. Thus, it is the correct answer.
c) Amino peptidase is produced in the small intestine of the body. It is concerned with breaking amino acids from peptide chains. In simple words, it helps in further breakdown of proteins in the small intestine so, clearly does not initiate digestion of proteins. Thus, it is an incorrect option.
d) Carboxyl peptidase is another enzyme that is produced in the small intestine and is concerned with further breakdown of protein. Therefore, it is also an incorrect option.

So, the correct answer is ‘Pepsin’.


Note:
Digestive system of vertebrates is quite complex and advanced. Every part of the system is concerned with some specific task leading to organised digestion of food. However, these tasks are completed by action of chemical based proteins called enzymes that are secreted by various parts of the digestive system. They work as a catalyst in breakdown reactions of foods and minerals.