Correct Response: C. The bile produced by the liver and stored in the gall bladder helps emulsify lipids (fats) in the duodenum. Bile salts are hydrophilic on one side and hydrophobic on the other side, and they tend to aggregate around droplets of lipids. The hydrophobic side is positioned toward the fat, and the hydrophilic side faces outward. The hydrophilic side prevents fat droplets coated with bile from re-aggregating into larger fat particles and exposes the fat's surface to enzymes. Bile salts emulsify fats and do not bond with amino acids in order to move them against the concentration gradient (A). Bile salts are secreted into the duodenum, which is part of the intestinal tract and is not part of the stomach (B). Bile salts adhere to lipids rather than to amino acids (D); it is pepsin that begins the process of breaking down protein in the stomach.
