Enzyme activity peaks match stomach's acidic pH

Steps:

• Recall stomach pH is acidic, typically 1.5–3.5, where enzymes like pepsin function.
• Examine graph: Identify enzyme with highest activity at low pH (around 2–4).
• Compare peaks: Enzyme A shows maximum activity in acidic range.
• Eliminate others: B, C, D peak at neutral or alkaline pH, unsuitable for stomach.

Why A is correct:

• Pepsin, a stomach enzyme, is active at pH 1.5–2.5 per enzyme-substrate complex stability in acids.

Why the others are wrong:

• B: Peaks at neutral pH ~7, typical for intestinal enzymes.
• C: Shows activity at slightly alkaline pH ~8, like pancreatic enzymes.
• D: Broad peak at pH 6–7, not acidic enough for stomach.

Final answer: A