Digestion processes in the gastrointestinal tract

Steps:

• Identify physical breakdown as mechanical processes like churning or grinding food.
• Identify chemical breakdown as enzymatic reactions that alter food molecules.
• Recall that the stomach uses muscles to mix and churn food (physical) while secreting hydrochloric acid and pepsin for protein digestion (chemical).
• Eliminate options not involved in both types of breakdown.

Why D is correct:

• The stomach performs both physical breakdown via peristalsis and muscular contractions and chemical breakdown via gastric juices containing pepsin and HCl, as defined in human digestive physiology.

Why the others are wrong:

• A. Colon: Primarily absorbs water and electrolytes; minimal breakdown occurs via bacteria, not both types actively.
• B. Liver: Produces bile for fat emulsification but does not directly break down food; it's an accessory organ.
• C. Rectum: Stores and expels waste; no digestion or breakdown happens here.

Final answer: D