The alveoli consists of different types of cell. It is here that gas exchange occurs. However, only certain special cells in the alveoli are thin enough to allow gas exchange. The two types of cells in the alveoli are the type 1 pneumocytes and the type 2 pneumocytes. The type 1 pneumocytes are the thin cells of the alveoli where gas exchange occurs.
They have very thin membranes allowing the gases to diffuse across the membrane easily. If the cells are thicker the gases won’t be able to diffuse and gas exchange won’t be possible.