The large muscular sac where mechanical digestion continues and protein digestion begins is the?

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

Answer: (A)

The key idea is where both mechanical processing of food and the first step of protein digestion occur. The stomach is a large, muscular sac that continues physical breakdown as it churns and mixes food with gastric juice. At the same time, it initiates protein digestion because the stomach’s glands release pepsinogen, which is activated to pepsin by the acidic environment created by hydrochloric acid. Pepsin then begins breaking proteins into smaller peptides. The stomach’s muscular action plus this early enzymatic activity explain why it’s the correct site. The esophagus mainly moves food along without digestion; the small intestine does most of the digestion and nutrient absorption (with protein digestion completed there by pancreatic and brush-border enzymes); the colon mainly handles water absorption.