The partial pressures (in mm Hg) of oxygen $(O_{2})$ and carbon dioxide $(C O_{2})$ at alveoli (the site of diffusion) are:

p O_{2} = 159 a n d p C O_{2} = 0.3

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p O_{2} = 104 and p C O_{2} = 40

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p O_{2} = 40 and p C O_{2} = 45

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p O_{2} = 95 and p C O_{2} = 40

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Solution

The correct option is B $p O_{2} = 104 and p C O_{2} = 40$
The pressure exerted by an individual gas in a mixture is known as its partial pressure. A gas will move from a region where its partial pressure is higher to a region where its partial pressure is lower.

Partial pressure of oxygen ( $p O_{2}$ ) in alveolar air is higher (104 mm of Hg) as compared to the partial pressure of carbon dioxide ( $p C O_{2}$ ) (40 mm of Hg).

In the deoxygenated blood, partial pressure of oxygen is lower (40 mm of Hg) as compared to partial pressure of carbon dioxide (45 mm of Hg).

Due to this difference in the partial pressures of oxygen between alveolar air and deoxygenated blood, oxygen diffuses from the alveoli into the blood capillaries.

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The partial pressures (in mm Hg) of oxygen (O2) and carbon dioxide (CO2) at alveoli (the site of diffusion) are:

The partial pressures (in mm Hg) of oxygen $(O_{2})$ and carbon dioxide $(C O_{2})$ at alveoli (the site of diffusion) are: