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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. [5] Some organisms have evolved intricate methods of circumventing hypertonicity. For example, saltwater is hypertonic to the fish that live in it.
Turgor pressure within the stomata regulates when the stomata can open and close, which plays a role in transpiration rates of the plant. This is also important because this function regulates water loss within the plant. Lower turgor pressure can mean that the cell has a low water concentration and closing the stomata would help to preserve water.
Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration of electrolytes (salts in solution which in this case is represented by body fluid) to keep the body fluids from becoming too diluted or concentrated.
The descriptor can apply to objects of different types, including cells, where one mechanism of crenation is the contraction of a cell after exposure to a hypertonic solution, due to the loss of water through osmosis.
Tonicity concept related to the transport of water towards the more concentrated aqueous solution (osmotic transport): In isotonic solutions, water flows equally into and out of the cell (equilibrium). In hypertonic solutions water flows out of the cell and the cell shrinks (plasmolysis).
The contractile vacuole is a specialized type of vacuole that regulates the quantity of water inside a cell.In freshwater environments, the concentration of solutes is hypotonic, lower outside than inside the cell.
Plasmolysis is the process in which cells lose water in a hypertonic solution. The reverse process, deplasmolysis or cytolysis, can occur if the cell is in a hypotonic solution resulting in a lower external osmotic pressure and a net flow of water into the cell.
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and matrix effects such as capillary action (which is caused by surface tension).