Q: How does the partial pressure of oxygen and carbon dioxide compare in atmospheric air versus alveolar air?  

Answer: B

The partial pressure of oxygen in atmospheric air is higher (159 mm Hg) compared to that in alveolar air (104 mm Hg). On the other hand, the partial pressure of carbon dioxide is lower (0.3 mm Hg) in atmospheric air compared to that in alveolar air (40 mm Hg). This difference in partial pressures of oxygen and carbon dioxide is due to the exchange of gases between alveoli and capillaries during respiration. Oxygen diffuses from alveoli into capillaries while carbon dioxide diffuses from capillaries into alveoli, leading to a decrease in partial pressure of oxygen and an increase in partial pressure of carbon dioxide in alveolar air.

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