Final answer:
Facilitated diffusion is the process where solutes move down their concentration gradient through the plasma membrane with the help of channel or carrier proteins, without energy expenditure by the cell.
Step-by-step explanation:
If diffusion is aided by channel and carrier proteins and the solute is still going down its concentration gradient, this process is known as facilitated diffusion. Facilitated diffusion is a type of passive transport where solutes move across the plasma membrane with assistance from transport proteins, like channel or carrier proteins, without the expenditure of energy from the cell. This process helps in moving substances that typically would not diffuse easily or quickly through the lipid bilayer due to their polarity or size, like glucose or certain ions. During facilitated diffusion, the concentration gradient acts as the driving force, and the involvement of specific membrane proteins ensures that the movement of molecules is regulated. For example, glucose transport proteins (GLUT) are a type of carrier protein that facilitates the entry of glucose molecules into a cell by changing their shape as the glucose binds.