Q.(a) Explain the process of digestion in the stomach. OR

The stomach churns food with acidic gastric juice, which activates the enzyme pepsin to begin breaking down proteins, converting the food into a semi-fluid chyme that moves on to the duodenum.

Answering part (a): When swallowed food (the bolus) enters the stomach through the cardiac sphincter, it is met by continuous secretion of gastric juice from the gastric glands lining the stomach wall. Gastric juice is a complex mixture: hydrochloric acid (HCl), secreted by the oxyntic (parietal) cells, creates a strongly acidic environment (pH around 1.5-2.5) inside the stomach; pepsinogen, secreted by chief (peptic) cells as an inactive precursor, is converted by this acidic environment into the active proteolytic enzyme pepsin; and mucus, secreted by mucous cells, coats and protects the stomach's own lining from being digested by the acid and pepsin. The muscular walls of the stomach undergo strong churning (peristaltic mixing) movements that thoroughly blend the food with gastric juice. Within this acidic environment, pepsin acts specifically on dietary proteins, breaking the long polypeptide chains down into smaller fragments called proteoses and peptones — this is only a partial digestion of protein, not complete breakdown to amino acids, which happens later in the small intestine. In infants, gastric juice also contains rennin (chymosin), which curdles milk protein (casein) so it can be acted upon by pepsin. Through the combined churning an …