Why does oxygen move from the alveoli into the blood of pulmonary capillaries?
Correct answer C. The partial pressure of oxygen in alveolar air is higher than in the blood
Explanation
Gas exchange occurs by simple diffusion. Alveolar pO₂ is about 100 mmHg, while blood arriving in pulmonary capillaries has about 40 mmHg, so oxygen diffuses down this gradient.
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