Facilitated diffusion is when a molecule or ion is moved from a high concentration to a low concentration with the help of a membrane protein.
Work Step by Step
Facilitated diffusion does not require ATP. It occurs when a molecule or ion is moved from a high to a low concentration with the assistance of a membrane protein. A membrane protein is needed because either the molecule is too large or the molecule is polar. A large molecule will not be able to pass through the cell membrane because of its size. A polar molecule will not be able to pass through a membrane due to the nonpolar interior of the cell membrane. Either a channel protein or a carrier protein will assist a particle in facilitated diffusion.