Question

Assertion (A): Exchange of oxygen and carbon dioxide occurs between blood vessels and alveoli. Reason(R): Oxygen diffuses from alveoli to blood vessels and carbon dioxide diffuses from blood vessels to alveoli. *​

Answer 1

Answer:

Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

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. The alveolus is the primary site of exchange as it has an extensive network of blood capillaries and consists of squamous epithelium. Due to the very intimate contact of blood capillaries with the alveoli, the exchange of gases takes place easily.