Question

required information
which of the following statements about partial pressures of gases in the lungs is true?
multiple choice
po2 in the lungs > po2 in the blood; pco2 in the lungs > pco2 in the blood
po2 in the lungs > po2 in the blood; pco2 in the lungs < pco2 in the blood
po2 in the lungs > po2 in the blood; pco2 in the lungs = pco2 in the blood
po2 in the lungs < po2 in the blood; pco2 in the lungs is < pco2 in the blood
po2 in the lungs < po2 in the blood; pco2 in the lungs > pco2 in the blood

Explanation:

Gas exchange in the lungs occurs due to partial pressure gradients. Oxygen ($O_2$) diffuses from an area of higher partial pressure to an area of lower partial pressure. So, $P_{O2}$ in the lungs (where air is taken in) is higher than $P_{O2}$ in the blood (which is relatively oxygen - depleted). Carbon dioxide ($CO_2$) diffuses in the opposite direction. The blood has a higher $P_{CO2}$ (as it has collected $CO_2$ from tissues) compared to the lungs (where $CO_2$ is being exhaled). So, $P_{CO2}$ in the lungs is less than $P_{CO2}$ in the blood.

Answer:

$P_{O2}$ in the lungs > $P_{O2}$ in the blood; $P_{CO2}$ in the lungs < $P_{CO2}$ in the blood (the second option in the multiple - choice list)