facilitated diffusion

**facilitated diffusion**

Facilitated diffusion is a biological process by which molecules are transported across cell membranes with the help of specialized carrier proteins or channel proteins. Unlike simple diffusion, which occurs directly through the lipid bilayer, facilitated diffusion allows substances that are polar, charged, or large to move down their concentration gradient more efficiently without the expenditure of cellular energy (ATP). This mechanism is essential for the transport of nutrients, ions, and waste products in and out of cells, maintaining cellular homeostasis.