Question

give reason- the wall of alveoli contains an extensive network of blood vessels

Answer 1

inside alevoli of lungs continious exchange of gas takes place.the walls of alevoli are covered with extensive network of blood vessels or capillaries in which oxygen from alevoli is dissolved and carried out by the blood to heat for pumping.in the same way carbon dioxide is also carried away by the blood vessels. Network of blood vessels are responsible for gaseous exchange that takes place in lungs.

hope this helps