Exchange between lung capillaries and alveoli is?

Ans. B Passive diffusionRef: Ganong's 25th ed. pg. 634-635* Exchange of oxygen and CO2 across the lung capillary and alveoli is passive diffusion.* Diffusion of O2 occur from alveoli to capillary (towards the pressure gradient), and diffusion of CO2 is in opposite direction (from capillary to alveoli).* Facilitated diffusion requires special carrier proteins.Extra Mile* Rate of diffusion is directly proportional to:# Pressure gradient# Surface area of respiratory membrane# Solubility of gas* Rate of diffusion is inversely proportional to:# Thickness of respiratory membrane# Molecular weight of gas