The organ in which most chemical digestion occurs is the?

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

Answer: (A)

Chemical digestion happens most extensively in the small intestine. Here, chyme from the stomach mixes with pancreatic enzymes—amylase for starch, lipase for fats, and proteases for proteins—and with bicarbonate to create the right pH. The lining has a vast surface area with villi and microvilli, and its brush-border enzymes (like disaccharidases and peptidases) finish digestion to monosaccharides and amino acids right where absorption occurs. The stomach does begin protein digestion with acid and pepsin, but most digestion is completed later. The mouth initiates carbohydrate digestion with salivary amylase, and the esophagus mainly moves food along with little to no digestion. So the small intestine is the key site for chemical digestion.