Water Balance of Cells with Cell Walls (Campbell Biology)
The cells of plants, prokaryotes, fungi, and some unicellular eukaryotes are surrounded by cell walls. When such a cell is immersed in a hypotonic solution—bathed in rainwater, for example—the cell wall helps maintain the cell’s water balance. Consider a plant cell. Like an animal cell, the plant cell swells as water enters by osmosis. However, the relatively inelastic cell wall will expand only so much before it exerts a back pressure on the cell, called turgor pressure, that opposes further water uptake. At this point, the cell is turgid (very firm), the healthy state for most plant cells. Plants that are not woody, such as most houseplants, depend for mechanical support on cells kept turgid by a surrounding hypotonic solution. If a plant’s cells and surroundings are isotonic, there is no net tendency for water to enter and the cells become flaccid (limp); the plant wilts.
However, a cell wall is of no advantage if the cell is immersed in a hypertonic environment. In this case, a plant cell, like an animal cell, will lose water to its surroundings and shrink. As the plant cell shrivels, its plasma membrane pulls away from the cell wall at multiple places. This phenomenon, called plasmolysis, causes the plant to wilt and can lead to plant death. The walled cells of bacteria and fungi also plasmolyze in hypertonic environments.
Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html
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