Passive transport – facilitated diffusion

Selective facilitaton of the diffusion of a given compound crossing a biological membrane by the presence of specific transport proteins (transporter, channels).

The membranes of cells work as effective barriers for the diffusion of many compounds. Cells, however, can allow the passage of selected compounds by integrating respective proteins (for example specific channels as depicted). This way, cells can control, which molecules may reach a given place at a given time.

Passive transport only allows the equilibration of concentrations differences. Processes resulting in the enrichment of compounds on one side of a biological membrane are designated as active transport and depend on the input of energy.