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Question : Assertion : Alveoli are the primary sites for exchange of gases. Reason : All factors in our body are favourable for diffusion of O_(2) from alveoli to tissus and that of CO_(2) from tissues to alveoli.

Answer»

If both ASSERTION and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true and reason is not the correct explanation of assertion
If assertion is true but reason is false.
If both assertion and reason are false.

Solution :The solubility of the gases as well as the thickness of the membranes involved in diffusion are important factors that affect the rate of diffusion. A gradient of partial pressure is presen for oxygen from alveoli to blood and blood to tissue. Similarly, a gradient of `CO_(2)` is present in the opposite direction i.e, from tissues to blood and blood to alveoli. It is further dependent on the solubility of the diffusing gases. As the solubility of `CO_(2)` is `20-25` times higher than that of `O_(2)`, the amount of `CO_(2)` that can diffuse through the diffusion membrane per unit difference in partial pressure is MUCH higher compared to that of `O_(2)`. THEREFORE all the factors in our body are favourable for diffusion of `O_(2)` from alveoli to tissues and that of `CO_(2)` from tissues to alveoli.
ALVEOLUS is the primary site of exchange as it has an extensive network of blood capillaries and consists of squamous epithelium. DUE to very intimate contact of blood capillaries with the alveoli, the exchange of gases takes place easily.


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