Osmotic potential
/ɑzˈmɑtɪk pəˈtɛnʃəl/
Definition
Osmotic potential describes the part of a cell’s water potential caused by dissolved substances such as sugars, salts, and organic acids. It is a biological concept used to predict water movement across a semipermeable membrane. Because solutes lower free water energy, osmotic potential is zero in pure water and becomes more negative as solute concentration rises. In plants, it helps explain water uptake, turgor pressure, and wilting.
Biological Role
- Driving water uptake: In roots, differences in osmotic potential help pull water from the soil into root cells, then onward through the plant when conditions support that movement.
- Supporting cell expansion: Growing tissues depend on a suitable osmotic potential to maintain turgor, the internal pressure that keeps cells firm and allows leaves, stems, and roots to expand.
- Link to drought and salinity: Dry soils and salty soils make water harder for roots to absorb because they lower the surrounding water potential, reducing the gradient plants rely on for uptake.
- Part of stress adjustment: Many plants respond to water stress by accumulating sugars, amino acids, or ions in their cells, which changes osmotic potential and helps preserve turgor during dehydration.
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