Which of the following describes mechanical digestion?

• A. Absorption of nutrients.
• B. Break down of food through chewing and swallowing.
• C. Secretion of digestive enzymes.
• D. Movement of chyme through the GI tract.

Answer: (B)

Mechanical digestion is about physically breaking food into smaller pieces to increase surface area for enzymes to act. In the mouth, chewing and grinding accomplish this by physically breaking down the food, with the tongue aiding in mixing it with saliva to form a manageable bolus. Swallowing helps move that bolus along the tract, but the actual breakdown is the chewing action. The other options describe nutrient absorption, enzyme secretion (chemical digestion), or movement through the GI tract (propulsion), which are different parts of digestion and not the physical fragmentation process.