Enzymes function optimally at specific pH levels

Steps:

• Identify that each enzyme has a unique optimal pH for maximum activity.
• Recall amylase digests starch in saliva and pancreas, optimal at neutral pH (6.7–7.0).
• Note lipase breaks down fats in the small intestine, optimal at neutral to slightly alkaline pH (7–8).
• Determine maltase hydrolyzes maltose in the small intestine, optimal at neutral pH (around 6–7).
• Confirm pepsin digests proteins in the stomach, optimal at low acidic pH (1.5–2.5).

Why D is correct:

• Pepsin is activated and functions at peak efficiency in the stomach's low pH environment (pH 1.5–3.5), as defined by its role in protein digestion under acidic conditions.

Why the others are wrong:

• A. Amylase: Optimal in neutral pH of mouth and pancreas, denatures in low pH.
• B. Lipase: Optimal in neutral-alkaline pH of small intestine, inactive in low pH.
• C. Maltase: Optimal in neutral pH of small intestine, not adapted to acidic conditions.

Final answer: D