Define and explain facilitated diffusion

Ans. Facilitated diffusion is also called carrier - mediated diffusion or transport by carrier protein. It occurs along concentration gradient assisted by carrier proteins e.g., diffusion of glucose in RBCs.
(a) The membrane proteins provide sites at which some molecules cross the membrane. They do not set up a concentration gradient for molecules to diffuse even if facilitated by proteins.
(b) Some special proteins aid to move substances across membranes without expenditure of ATP energy.
© It cannot cause net transport of molecules from a low to a high concentrations as it requires input of energy.
(d) Facilitated diffusion is stereospecific.