Final answer:
Pepsin is an enzyme that is essential for breaking down proteins in the stomach, which is a necessary step in the digestion process.
Step-by-step explanation:
Pepsin is necessary for the stomach to break down proteins. Pepsin is a digestive enzyme produced in the stomach that helps in the breakdown of proteins into smaller peptides. When proteins are ingested, pepsin is secreted by the stomach's cells in an inactive form called pepsinogen. When pepsinogen comes into contact with hydrochloric acid in the stomach, it is converted into pepsin. Pepsin works optimally in the acidic environment of the stomach and helps in the digestion of dietary proteins.