Facilitated diffusion (Wiki)
A facilitated diffusion protein speeds the movement of a chemical through a membrane in the absence of energy input; therefore, the transported chemical can move only down a concentration gradient. This can be accomplished by the formation of a high-specificity pore or channel
that spans the membrane. These polar "holes" through the membrane are
lined by specific amino acids residues that lower the energy barrier to
the movement of polar molecules."
"Transport of substances across a biological membrane from an area of higher concentration to an area of lower concentration by means of a carrier molecule. Since the substances move along the direction of their concentration gradients, energy is not required.
For example, polar molecules and charged ions dissolved in water can not diffuse freely across cell membrane due to its hydrophobic lipids. They can only be transported across membranes by proteins forming transmembranechannels. Larger molecules are transported by transmembrane carrier proteins, such as permeases that change their conformation as the molecules are carried through, for example glucose or amino acids.
Membrane Transport Protein (Wiki)
" general term for a membrane protein that increases the permeability of the plasma membrane to a particularmolecule, by a process not requiring metabolic energy.