A) simple diffusion
B) active transport
C) passive transport
D) fascilitated diffusion
Correct Answer: A
Solution :
Maximum gaseous exchange between blood (dissolved phase) and alveolar (lungs) air (gaseous phase) across respiratory membrane occurs by simple diffusion. The exchange depends upon the concentration gradients (partial pressure) of the concerned gases in blood and alveolar air. Both\[{{\text{O}}_{\text{2}}}\] and \[\text{C}{{\text{O}}_{2}}\]are highly and equally soluble in lipid and hence easily diffusible through cell membrane. In passive transport an ion or molecule crossing a membrane moves down its concentration gradient and no metabolic energy is consumed. Facilitated diffusion is special type of passive transport where specific permeases in membrane facilitate the crossing of solutes. Active transport uses specific transport protein called pumps which use metabolic energy (ATP) to move ions or molecules against their concentration gradient.
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