Water Balance of Cells Without Walls• Tonicity is the ability of a surrounding solution tocause a cell to gain or lose water. à ⽤以描述半透膜內外之滲透壓的相對⾼低。• Isotonic solution: Solute concentration is the sameas that inside the cell; no net water movementacross the plasma membrane.• Hypertonic solution: Solute concentration isgreater than that inside the cell; cell loses water.• Hypotonic solution: Solute concentration is lessthan that inside the cell; cell gains water.