Behaviour of a red blood cell in a hypotonic medium. When a cell is placed in a hypotonic solution, the solute concentration outside the cell is lower than that inside the cell. As a result, there will be a net flow of water into the cell by osmosis, and the cell will gain volume until the intracellular and extracellular fluids are in osmotic equilibrium. If placed in a hypotonic solution, a red blood cell will swell up and may burst (haemolysis).