Oxygen and carbon dioxide are exchanged in the lungs and through all cell membranes by:
a. Active transport
b. Diffusion
c. Filtration
d. Osmosis
The pressure gradient for O2 is much less than the pressure gradient for CO2, but because of hemoglobin, more O2 can be carried in the blood.
Because the pressure gradient for O2 is greater than the pressure gradient for CO2, more molecules of O2 will be exchanged in the alveoli than molecules of CO2.
Most molecules of O2 are carried by hemoglobin, but it is the gradient between the plasma and the alveoli that determines the movement of O2 in and out of the blood.
O2 is 20 times more soluble than CO2, meaning that much more O2 can be carried in the blood plasma than CO2.