In external respiration, the partial pressures are: A)alveoli: high PO₂, low PCO₂; pulmonary capillaries: low PO₂, high PCO₂ B)alveoli: high PO₂, high PCO₂; pulmonary capillaries: low PO₂, low PCO₂ C)alveoli: low PO₂, high PCO₂; pulmonary capillaries: high PO₂, low PCO₂ D)alveoli: low PO₂, low PCO₂; pulmonary capillaries: high PO₂, high PCO₂

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In external respiration, oxygen diffuses from the alveoli (where its partial pressure is high) into the blood of the pulmonary capillaries (where its partial pressure is low), and carbon dioxide diffuses in the opposite direction, from the blood (where its partial pressure is high) into the alveoli (where its partial pressure is low).

In External Respiration, the Partial Pressures Are