What is it called when molecules move from low to high concentration across plasma membranes?

Answer: Osmosis

Explanation: Osmosis is a process in which water move from an area of low solute concentration to an area of high solute concentration through a selectively permeable membrane. For osmosis to occur, it must be through a selectively permeable membrane. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.