External respiration refers to gas exchange in which location?

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External respiration is the gas exchange that occurs between the air in the lungs and the blood. It happens across the thin alveolar–capillary membrane in the lungs, where diffusion moves oxygen from the alveolar air into the blood and carbon dioxide from the blood into the alveolar air. This exchange is driven by differences in partial pressures: oxygen in the alveoli is higher than in the blood, while carbon dioxide is higher in the blood than in the alveolar air. The result is oxygenated blood ready for delivery to tissues and carbon dioxide removed from the body when you exhale. This is distinct from gas exchange in body tissues (internal respiration), which occurs at tissue capillaries; gas transport in the blood, which is merely moving gases through the bloodstream; and cellular respiration, which is the cellular use of oxygen to produce energy.