Solution :
i) Alveoli are pouch-like air sac that is made up of simple squamous epithelium. ii) The alveoli are thin-walled and richly supplied with a network of blood vessels to facilitate the exchange of gases between blood in the capillaries and the air inside the alveoli. iii) These alveoli are balloon-like structures which provide the maximum surface area for the exchange of gases.
iv) It has a thin cell wall to facilitate gaseous exchange.
v) The presence of millions of alveoli in the lungs provides ample surface area to facilitate gaseous exchange between the air in alveoli and blood in surrounding capillaries.
vi) Oxygen (O2) diffuses across the alveolar and capillary walls into the bloodstream while carbon dioxide (CO2) diffuses from blood across the mentioned walls into the alveoli.