Amylase Inactivation by Stomach Acidity

Steps:

• Starch digestion begins in the mouth with salivary amylase, which breaks down starch into maltose.
• In the duodenum, pancreatic amylase continues this process in a neutral pH environment.
• Food enters the stomach, where hydrochloric acid lowers the pH to 1-2 for protein digestion.
• This acidic pH denatures amylase enzymes, altering their shape and halting starch breakdown.

Why C is correct:

• Enzymes like amylase have an optimal pH (around 6-7); stomach acidity denatures the protein structure, inactivating it per enzyme kinetics principles.

Why the others are wrong:

• A: Most starch remains undigested when reaching the stomach, as mouth digestion is brief.
• B: While true, the stomach lacks amylase production, the key issue is inactivation of existing salivary amylase by acid.
• D: Body temperature (37°C) is optimal for amylase and uniform throughout the digestive tract.

Final answer: C