Tonicitat: diferència entre les revisions

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==Efecte en les cèl·lules==
En les cèl·lules animals un ambient hipertònic força l'aigua a abandonar la cèl·lula i per tant la forma de la cèl·lula es distorsiona i s'arruga, un estat conegut com [[crenació]]. En les cèl·lules vegetals l'efecte és més dramàtic . ''The flexible [[cell membrane]] pulls away from the rigid [[cell wall]], but remains joined to the cell wall at points called [[plasmodesmata]]. The cell takes on the appearance of a [[pincushion]], and the plasmodesmata almost cease to function because they become constricted — a condition known as [[plasmolysis]]. In plant cells the terms isotonic, hypotonic and hypertonic cannot strictly be used accurately because the pressure exerted by the cell wall significantly affects the [[osmotic equilibrium point]]''.
 
''Some organisms have evolved intricate methods of circumventing hypertonicity. For example, [[Seawater|saltwater]] is hypertonic to the [[fish]] that live in it. They need a large surface area in their [[gill]]s in contact with seawater for [[gas exchange]], thus they lose water osmotically to the sea from gill cells. They respond to the loss by drinking large amounts of saltwater, and actively [[excretion|excreting]] the excess salt. This process is called [[osmoregulation]]''.
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