Final answer:
Facilitated diffusion is the passive transport of solutes through transport proteins in the plasma membrane. It allows polar molecules like glucose, amino acids, and ions to enter and leave cells down their concentration gradient.
Step-by-step explanation:
In facilitated diffusion (passive transport), solutes go through transport proteins in the plasma membrane. These transport proteins, such as channel proteins, gated channel proteins, and carrier proteins, facilitate the movement of solutes down their concentration gradient. This process does not require energy and allows polar molecules like glucose, amino acids, and ions to enter and leave cells.