Stomach acid kills ingested bacteria

Steps:

• Identify the function: The organ must produce an acid to eliminate bacteria in food during digestion.
• Recall digestive process: Food enters the mouth, then stomach, where initial breakdown occurs.
• Focus on stomach role: It secretes hydrochloric acid to create a low pH environment.
• Eliminate non-acidic organs: Liver, pancreas, and salivary glands do not produce bactericidal acids.

Why D is correct:

• The stomach produces hydrochloric acid (HCl), which lowers pH to 1.5–3.5, denaturing proteins and killing bacteria per the definition of gastric acid's antimicrobial role.

Why the others are wrong:

• A. Liver: Produces bile for emulsifying fats, not acids for bacteria.
• B. Pancreas: Secretes alkaline bicarbonate to neutralize stomach acid, aiding enzyme function.
• C. Salivary gland: Produces saliva with enzymes like amylase for starch breakdown, lacking bactericidal acid.

Final answer: D