Osmosis
/ɑzˈmoʊsɪs/
Definition
Osmosis is a biological process in which water moves across a selectively permeable membrane, such as a plant cell membrane, from an area with lower dissolved solute concentration to one with higher solute concentration. In plants, this movement helps roots take up water and helps cells maintain turgor, the internal pressure that keeps tissues firm. Unlike general diffusion, osmosis refers specifically to the movement of water through a membrane.
Biological Role
- Water uptake by roots: In roots, osmosis helps move water from the soil into root hairs and then into surrounding cells, supporting the first step of water entry into the plant.
- Cell firmness and leaf support: By filling the vacuole, a fluid-filled storage compartment, osmosis creates turgor pressure. This internal pressure keeps stems and leaves firm and helps young tissues stay upright.
- Stomatal opening and closing: Guard cells around each stoma, a tiny leaf pore, gain or lose water through osmosis. Their change in pressure helps control gas exchange and water loss.
- Salt stress and wilting: When soil contains too much dissolved salt, water becomes harder for roots to absorb by osmosis. Plants may then wilt, show leaf scorch, or grow poorly even when the soil looks moist.
Related Terms
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Vacuole
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Overwatering
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