The mechanism of action of surfactant is

Ans. is 'd' i.e. Breaks the structure of water in the alveoli The water molecules on the surface of water (at air-water interphase) have an especially strong attraction for one another. This results in the water surface to contract producing surface tension.Thus the water molecules lining the alveoli produce an elastic contractile force due to surface tension which causes the alveoli to collapse.This surface tension force of water molecules is broken by surfactant (a mixture of phospholipids, proteins and ions, most important phospholipid of which is dipalmitoylphosphatidyl-choline-DPCC). It is secreted by type II alveolar epithelial cells and lines the alveoli.The phospholipid molecules have a hydrophilic head and two parallel hydrophobic 'tails'. Thus only head part of the molecule dissolves in the fluid lining the alveolar surface and the hydrophobic tails face the alveolar lumen. This new surface thus formed of the surfactant has a significantly reduced surface tension than the water molecules.By reducing the surface tension, surfactant serves two purposes:Prevents the alveoli from collapsingPrevents pulmonary edema.