<P> Reverse osmosis is a separation process that uses pressure to force a solvent through a semi-permeable membrane that retains the solute on one side and allows the pure solvent to pass to the other side, forcing it from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure . </P> <P> Osmosis may be used directly to achieve separation of water from a solution containing unwanted solutes . A "draw" solution of higher osmotic pressure than the feed solution is used to induce a net flow of water through a semi-permeable membrane, such that the feed solution becomes concentrated as the draw solution becomes dilute . The diluted draw solution may then be used directly (as with an ingestible solute like glucose), or sent to a secondary separation process for the removal of the draw solute . This secondary separation can be more efficient than a reverse osmosis process would be alone, depending on the draw solute used and the feedwater treated . Forward osmosis is an area of ongoing research, focusing on applications in desalination, water purification, water treatment, food processing, etc . </P>

The movement of water and ions through a cell membrane depends on what property of the membrane