Osmosis is the movement of water across a membrane that is permeable to water but no to certain substances (solutes), such as sugar dissolved in the water. Given two solutions separated by such a semipermeable membrane, water will flow from the solution containing less dissolved material into the solution containing a higher concentration of solutes. Osmosis is important in biological systems, as many biological membranes are semipermeable. These membranes are impermeable to organic solutes with large molecules, such as polysaccharides, while permeable to water and small, uncharged solutes. Permeability may depend on solubility properties, charge, or chemistry, as well as solute size. Permeability may depend on solubility properties, charge, or chemistry, as well as solute size. Osmosis provides the primary means by which water is transported into and out of cells.