* If the medium is ''hypertonic'', the water concentration inside the cell is greater. This leads to net movement of water out of the cell. Animal cells shrivel up; plant cells become ''plasmolysed'' (the cell membrane pulls away from the cell wall in places as the cytoplasm shrinks).
''Tonicity'' is also applied to the elastic tension of living muscles, arteries, etc. that facilitates response to stimuli. Clinically, this is referred to as ''tonus'' (See ''[[muscle tone]]'').