Hypertonic
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In biology, a hypertonic cell environment has a higher concentration of solutes outside of the animal or plant cell. Osmosis causes water to flow out of the cell. If enough water is removed in this way, the cytoplasm will have such a small concentration of water that the cell has difficulty functioning.
A solution which has a higher concentration of solutes than that in a cell is said to be hypotonic. This solution has more solute particles and, therefore, relatively less water than the cell contents.
[edit] Living in a Hypertonic environment
In plant cells, the effect is more dramatic. The cell membrane pulls away from the cell wall, but the cell remains joined to the adjacent cells at points called plasmodesmata. Thus, the cell takes on the appearance of a pincushion, with the plasmodesmata almost ceasing to function because they have become so constricted. This condition is known as plasmolysis.
In animal cells, being in a hypertonic environment results in crenation, where the shape of the cell becomes distorted and wrinkled as water leaves the cell.
Saltwater is hypertonic to the fish that live in it. The fish cannot isolate themselves from osmotic water loss, because they need a large surface area in their gills for gas exchange. They respond by drinking large amounts of water, and excreting the salt through their kidneys.
The opposite of hypertonic is hypotonic, where the net movement of water is into the cell; the intermediate state is called isotonic, where there is no net movement of water. This does not mean, however, that water is not moving; it means that water is moving both ways but with equal force, so the water concentration on either side of the cell membrane ultimately does not change. When a hypotonic cell dies, its remains are absorbed by other similar hypotonic cells.
