What is the definition of facilitated diffusion?

Facilitated diffusion is defined as the movement of specific molecules through protein channels in the cell membrane. This process allows certain substances, which may be polar or larger molecules that cannot easily pass through the lipid bilayer, to cross the membrane efficiently. The presence of specialized protein channels or carriers facilitates this process, enabling the molecules to move down their concentration gradient without the expenditure of energy.

In facilitated diffusion, the proteins serve as gateways, providing a selective pathway allowing specific ions or molecules to enter or exit the cell, which is crucial for maintaining homeostasis and supporting cellular functions. Since this process is passive, it relies solely on the concentration difference of the solute, emphasizing the role of these protein channels in assisting molecules that would otherwise not permeate the membrane effectively.