Which organ is primarily involved in chemical digestion via gastric acid?

• A. Mouth
• B. Small intestine
• C. Esophagus
• D. Stomach

Answer: (D)

Gastric acid digestion happens in the stomach. Here, parietal cells secrete hydrochloric acid, creating a strongly acidic environment that activates pepsinogen into the enzyme pepsin. Pepsin then begins digesting proteins by breaking peptide bonds, turning large proteins into smaller peptides. The stomach also churns food and protects its lining with mucus, but the crucial chemical digestion driven by acid is centered in this organ. The other organs listed play different roles: the mouth begins some digestion with saliva, the small intestine handles most chemical digestion and nutrient absorption with pancreatic enzymes and bile, and the esophagus mainly moves food along.