Diffusion is a type of transport that moves molecules or compounds in or out of a cell. There are three main types of diffusion, which include simple diffusion, channel diffusion and facilitated diffusion.
Simple diffusion occurs when small, nonpolar molecules transport through the selectively permeable cell membrane. Molecules that are able to pass through the membrane must be hydrophobic so that they can move through the hydrophobic region of the lipid bilayer region. Simple diffusion is a passive process that does not require energy or a membrane protein.
Channel diffusion is also a type of passive transport that occurs with the help of membrane transport proteins. These proteins are embedded in the cell membrane and can open and close to allow molecules or compounds into or out of the cell. Channel diffusion is easily regulated by the membrane proteins. In general, ions and charged particles are the types of molecules that utilize channel diffusion.
The final type of diffusion is facilitated diffusion. This type of diffusion also utilizes protein carriers that are embedded into the cell's membrane. These protein carriers bind to compounds, then change their shape. Next, they release the compound into or out of the cell and regain their shape. Facilitated diffusion is also a passive process.