Diffusional transport mechanism:

While a simple diffusion process occurring across a semipermeable membrane is coupled along with chemical reactions within the membrane, the net diffusional rate of permeating species by the membrane might be greatly enhanced. Like a diffusional permeation is known as facilitated diffusional transport. Facilitated diffusion occurs in liquid membrane systems. This mechanism needs a carrier substance within the membrane that shuttles back and forth among the two sides of the membrane carrying the permeating substance through combining with it. Forward reaction of chemical combination among the carrier and the permeating substance takes place on one side of the membrane and the backward reaction of dissociation within carrier and the permeant occurs on the other side.