Final answer:
Facilitated diffusion is the spontaneous passage of molecules or ions across membranes through specific transmembrane proteins. It does not require energy and occurs when molecules move down a concentration gradient through specific protein channels.
Step-by-step explanation:
In facilitated diffusion, materials diffuse across the plasma membrane with the help of membrane proteins. This process does not require energy and occurs when molecules move down a concentration gradient through specific protein channels in the membrane.
Facilitated diffusion is commonly used by polar molecules like glucose, amino acids, and ions that are repelled by the hydrophobic parts of the cell membrane.