What characterizes facilitated diffusion?

Facilitated diffusion is characterized primarily by its dependence on integral proteins to facilitate the transport of substances across a biological membrane. This process is a type of passive transport, meaning that it does not require energy input from ATP. Instead, facilitated diffusion allows specific molecules, often polar or larger than typical small molecules, to move down their concentration gradient with the assistance of transmembrane proteins. These proteins can form channels or act as carriers to effectively transport substances that cannot freely diffuse through the lipid bilayer of the membrane due to their size or polarity.

This mechanism is critical for the uptake of essential molecules such as glucose and ions, allowing them to cross cell membranes efficiently and selectively, thus maintaining the appropriate concentrations within cells necessary for various biological functions. The role of integral proteins is crucial in this process, distinguishing facilitated diffusion from simple diffusion, which does not involve protein assistance.