facilitated diffusion The transport of molecules across the plasma membrane of a living cell by a process that involves a specific transmembrane carrier (see transport protein) located within the plasma membrane but does not require expenditure of energy by the cell. The carrier combines with a molecule at one face of the membrane, then changes shape so the molecule is moved through the membrane and released at the opposite face. It enables the diffusion through the membrane of molecules that otherwise could not pass through. Compare active transport.

facilitated diffusion A carrier-mediated membrane-transport mechanism, driven by a diffusion gradient, that is important in the transport of materials into and out of cells.

facilitated diffusion A carrier-mediated membrane transport mechanism that is driven by a diffusion gradient.