IB Biology Exam Prep

Category - Biology

Which of the following best describes the function of bile salts in the process of digestion?
  1. Bonding to the surface of amino acids to allow them to be actively pumped against the concentration gradient by epithelial cells.
  2. Lowering stomach pH to produce the acid environment necessary for the proper functioning of enzymes and the destruction of pathogens.
  3. Coating fat droplets and preventing them from coalescing to expose more surface of the droplets to the action of hydrolytic enzymes..
  4. Cleaving bonds of amino acids to break long polypeptide chains into smaller segments that can be more easily absorbed.
Explanation
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.
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