Facilitated diffusion is considered passive transport because substances pass through a cell membrane with the assistance of a protein carrier, and no cellular energy is used in this process. Solutes use facilitated diffusion to move from areas of higher concentration to areas of lower concentration.
Facilitated diffusion is a method of passive transport that allows sizable, charged or hydrophilic molecules, which cannot use the process of simple diffusion, to travel through the cell membrane with the aid of membrane proteins. These proteins are found throughout the phospholipid layer and connect the interior and exterior of the cell. Without the protection of these membrane proteins, the ions and polar molecules that use passive transport would be repelled by the hydrophobic parts of the cell membrane, rendering diffusion impossible. This process is also known as facilitated transport.
There are two different membrane proteins used in the process of facilitated diffusion: carrier proteins and channel proteins. Carrier proteins bind to a molecule in order to transport it through the cell membrane. Channel proteins create a passage that allows molecules and ions to diffuse through the cell membrane, allowing passage with various signals. This passage is forged within a hydrophilic region of the cell membrane.