What is the partial pressure (in mm Hg) of O₂ in :-
i) Alveoli
ii) Oxygenated blood
iii) Tissues

i- 104, ii- 95, iii- 40

The correct answer is Option (4) -i- 104, ii- 95, iii- 40

Partial pressure refers to the pressure exerted by an individual gas within a mixture of gases. The alveoli, which are small sac-like structures in the lungs, serve as the primary location for the exchange of gases such as oxygen and carbon dioxide. This gas exchange process occurs through diffusion, relying on differences in pressure gradients. Put simply, gases move from areas of higher pressure to lower pressure. Besides pressure differences, the rate of diffusion is also influenced by gas solubility and the thickness of the membrane through which gases move. Oxygen is exchanged between the alveoli and blood, then further transported from the blood to body tissues. Conversely, carbon dioxide exchange occurs from body tissues to the blood, and subsequently from the blood to the alveoli for elimination.

The partial pressure of O₂ in :-

i) Alveoli - 104 mm Hg

ii) Oxygenated blood - 95 mm Hg

iii) Tissues- 40