Biological Systems MCAT Practice Exam

The primary function of gastric acid (hydrochloric acid, HCl) in the stomach is to destroy microorganisms. The acidic environment created by gastric acid plays a critical role in the digestive process by maintaining a low pH, which is inhospitable to many pathogens and helps to ensure that the ingested food is sanitized before it moves further into the gastrointestinal tract. This acid not only serves to eliminate harmful bacteria and other microbes that could potentially cause infections or illness, but it also aids in the denaturation of proteins, making them easier for digestive enzymes to break down. In addition, the acidic environment activates pepsinogen, a precursor enzyme that converts to pepsin, which digests proteins. While the other functions suggested by the other choices—like breaking down carbohydrates, absorbing nutrients, and secreting mucus—are important in the overall digestive process, they are not the primary role of gastric acid. For example, the breakdown of carbohydrates primarily occurs in the mouth and small intestine, nutrient absorption mostly takes place in the small intestine, and mucus is produced to protect the stomach lining from the acidic environment. Therefore, the role of gastric acid in destroying microorganisms is crucial for maintaining gut health and aiding digestion.