CO2 diffuses more easily through the respiratory membrane than 02 because it is:

More soluble in plasma Diffusion of gases through the tissues or respiratory membrane depends on the solubility of the gas in lipids; but since all the gases of respiratory impoance are all highly soluble in lipids the diffusion through the tissues would depend on diffusion of gases in tissue water. The diffusion of gases through fluid depends on multiple factors (1. the solubility of the gas in the fluid, 2. the cross-sectional area of the fluid, 3. the distance through which the gas must diffuse, 4.the molecular weight of the gas, and 5. the temperature of the fluid.] of which the two which are characterstics of the gas itself are - Solubility in fluid & - Molecular weight. The diffusion coefficient of the gas is directly propoional to the solubility and inversely propoional to the square root of the molecular weight. Diffusion coefficient = Solubility/ Molecular weight Diffusion coeffiecient of: Oxygen ---- 1.0 Carbon dioxide ---- 20.3 Carbon dioxide despite having higher molecular weight than Oxygen, has a very high diffusion coefficient because of its very high solubility in plasma (about 22 times).