Which organ is primarily responsible for absorbing water and electrolytes from indigestible food matter?

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

Answer: (A)

Water and electrolyte reabsorption from indigestible matter happens mainly in the large intestine. After most nutrients have been absorbed earlier in the digestive tract, the remaining chyme enters the colon. There, the lining actively pulls out ions like sodium and chloride, and water follows by osmosis, producing a more solid stool. This reclaiming of water is essential for keeping the body hydrated and balancing electrolytes. The large intestine also hosts bacteria that ferment some fibers, but the key function tied to this question is turning liquid or semi-liquid chyme into feces by removing water and electrolytes. By contrast, the stomach does some limited water absorption, the small intestine handles most nutrient absorption (and a portion of water), and the esophagus mainly serves as a passageway.