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Pressure exerted by cytoplasm resulting in a pressing of the plasma membrane against a containing cell wall.
Turgidity is what can occur given cell suspension within a hypotonic environment. Plant cells are "happiest" when they display turgidity where the contrast, as seen given isotonicity, is a limpness known as flaccidity. Bacteria too prefer to exist in a turgid state where the contrast, plasmolysis, interferes with metabolism and growth. Indeed, one approach to food preservation is to create hypertonicity within foods, such as high salt or sugar concentrations, to prevent turgidity/encourage plasmolysis.
Turgidity is what can occur when cells are suspended in dilute solutions and/or supplied with water containing low solute concentrations (e.g., tap or rain water). As water evaporates, however, solutes are left behind, concentrating the aqueous solution. This drives the solution from one that is hypotonic to one that is isotonic and then hypertonic. The leaves of plants tend to droop when sufficient water has evaporated without replacement that their cells are bathed in an isotonic rather than hypotonic solution.
Note that animal cells lack cell walls and are normally bathed in an isotonic solution. Animal cells therefore both do not normally display turgidity and in fact cannot display turgidity but rather lyse – burst – given exposure to hypotonic solutions.
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