What does facilitated diffusion primarily involve?

Facilitated diffusion primarily involves the movement of molecules across a cell membrane through specialized protein channels. This process is essential for transporting substances that cannot readily diffuse through the lipid bilayer due to their size, charge, or polarity. The channel proteins provide a pathway that allows these specific molecules to move down their concentration gradient, from areas of higher concentration to areas of lower concentration, without the need for energy.

Selective permeability is a key aspect of facilitated diffusion, as the channel proteins are specific to certain substances, thereby ensuring that only particular molecules can enter or exit the cell. This selectivity is crucial for maintaining the cell's internal environment and properly regulating the transport of essential nutrients and ions.

Other processes mentioned, such as energy-dependent transport, involve active mechanisms that require ATP to move substances against their concentration gradients. Bulk transport of large particles refers to processes like endocytosis and exocytosis, which involve membrane invagination or fusion rather than diffusion through specific channels. In contrast, facilitated diffusion is a passive transport method reflecting the principles of concentration gradients and membrane permeability.