Factors Maintaining Alveolar Oxygen Gradient

Steps:

• Identify role of statement 1: Continuous breathing replenishes alveolar oxygen, keeping its concentration high.
• Identify role of statement 2: Blood circulation delivers deoxygenated blood, maintaining low oxygen in capillaries.
• Interpret statement 3: CO2 efflux from red blood cells reduces acidity, shifting hemoglobin's affinity toward oxygen binding (Bohr effect).
• Combine effects: All three sustain a steep gradient for diffusion per Fick's law.

Why A is correct:

• All statements align with Fick's law of diffusion, where rate ∝ concentration gradient; fresh O2 supply, low-O2 blood inflow, and CO2 removal maximize the Δ[O2] between alveolus and blood.

Why the others are wrong:

• B omits CO2 removal, which is essential for efficient oxygen loading in hemoglobin.
• C omits blood flow, preventing replenishment of low-O2 blood for ongoing exchange.
• D omits breathing, which fails to sustain high alveolar O2 levels.

Final answer: A