Which of the following is NOT a function of dilute hydrochloric acid secreted in the stomach of man?

Analyze the question: We need the option that is NOT a function of HCl in the stomach. Four options are real functions, and one is false.

Concept: The stomach's gastric glands secrete:

• Pepsinogen (inactive) from chief cells
• Hydrochloric acid from parietal (oxyntic) cells

Functions of HCl in the stomach:

1. It makes the stomach contents acidic (about pH 1.5-2), which is the optimum pH for pepsin. (Option A is true.)
2. It converts inactive pepsinogen into active pepsin. (Option B is true.)
3. It stops the action of ptyalin (salivary amylase), which works in a slightly alkaline or neutral medium. The acid denatures it. (Option D is true.)
4. It kills bacteria and other micro-organisms taken in with food. (Option E is true.)
5. It does not inactivate pepsin. Pepsin works best in acid, so HCl creates the conditions for it to work. (Option C is false.)

Step-by-step solution:

• A: acidifies the contents is a real function.
• B: activates pepsin is a real function.
• C: inactivates pepsin is the opposite of what happens, so it is not a function.
• D: inactivates ptyalin is a real function.
• E: kills micro-organisms is a real function.

**Answer: C.

Exam tip: Remember "HCl helps pepsin, hurts ptyalin." In the stomach, acid activates pepsin but stops salivary amylase. Pepsin is inactivated only when the pH rises, such as in the alkaline duodenum. In "NOT" questions, check each option and pick the one that is false.