PASSIVE TRANSPORT: FACILITATED DIFFUSION
Facilitated diffusion is the diffusion of a substance across a membrane. It is "facilitated" because a transport protein in the membrane enhances the transport of the substance across the membrane.

The involvement of the transport protein makes facilitated diffusion a type of carrier-mediated transport, although it is passive.

Note: The transport membrane is specific to the substance being transported, that is, it only transports that substance. Glucose, which is needed in large amounts by cells for energy, is one substance commonly transported into cells by facilitated diffusion.