1. Tardigrade
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  3. Biology
  4. Assertion: Alveoli are the primary sites for exchange of gases. Reason: All factors in our body are favourable for diffusion of O2 from alveoli to tissues and that of CO2 from tissues to alveoli.

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Q. 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 tissues and that of $CO_2$ from tissues to alveoli.

Breathing and Exchange of Gases

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 present 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.