Red Blood Cell Shape in Hypotonic Solutions: Osmosis & Hemolysis

When a red blood cell is placed in a hypotonic solution, the concentration of solutes outside the cell is lower than the concentration of solutes inside the cell. This causes water to move into the cell by osmosis, causing the cell to swell and become spherical. The lack of ability of the red blood cell membrane to resist this swelling is due to the absence of a cell wall.

Eventually the membrane ruptures and haemolyzes. The exact appearance of the red cell as it ruptures depends on the tonicity of the solution it is placed in.