Answer: Solute movement can only proceed down a concentration gradient.
Explanation:
In cell membrane, solute can be transported by various means from passive to active transport systems.
During facilitated diffusion however, solutes are HELPED to be transported AGAINST concentration gradient (from a region of low to high concentration) across the cell membrane by a special kind of vehicle (PROTEIN) present within the cell membrane.
Thus, it is NOT correct to say Facilitated diffusion occurs ONLY down the concentration gradient