Final answer:
Complex proteins are digested into amino acids by the secretions of hydrochloric acid (HCl) and pepsin in the stomach, with further breakdown by enzymes in the small intestine.
Step-by-step explanation:
To digest complex proteins into single amino acids for absorption, certain secretions are necessary. The correct answer to the question of which secretions are needed is A) hydrochloric acid and pepsin in the stomach. Hydrochloric acid (HCl) denatures proteins, exposing their peptide chains to enzymatic action, and pepsin begins the process of breaking down these proteins into smaller polypeptides and amino acids.
This process is initiated in the stomach and is continued in the small intestine where other enzymes, including trypsin and chymotrypsin from the pancreas, further contribute to the digestion of proteins into amino acids. Pepsinogen is released from the chief cells in the stomach and is converted to active pepsin in the presence of the acidic environment that is created by HCl.
The secretion needed to digest complex proteins into single amino acids for absorption is hydrochloric acid and pepsin in the stomach. When protein-rich foods enter the stomach, they are greeted by a mixture of the enzyme pepsin and hydrochloric acid (HCl). The HCl denatures proteins within food, and pepsin cuts proteins into smaller polypeptides and their constituent amino acids.