Final answer:
In facilitated diffusion, molecules move down a concentration gradient using special membrane proteins, a process that doesn't require energy.
Step-by-step explanation:
In facilitated diffusion, molecules move down a concentration gradient, which means they move from an area of higher concentration to an area where they are less concentrated. This process relies on specific membrane receptors or channel proteins to help the molecules move across the plasma membrane. Unlike active transport, facilitated diffusion does not require energy because molecules are moving down the concentration gradient. This is a form of passive transport. An example of facilitated diffusion is the movement of glucose and, in certain situations, Na+ ions, through the cell membrane.