Question

Why does carbon dioxide enter the blood vessels in the tissues but diffuse out of the blood vessels into the alveoli in the lungs?

Answer 1

This is due to the difference in the concentration of carbon dioxide on both sides of the membrane. In lungs the concentration of carbon dioxide is less in alveoli and more in blood vessels so carbon dioxide diffuse into the alveoli and goes out through nose. Where as concentration carbon dioxide near the tissues is more in tissue and less in blood vessels so carbon dioxide diffuse into the blood vessels.