water potential Symbol Ψ. The difference between the chemical potential of the water in a biological system and the chemical potential of pure water at the same temperature and pressure. It is manifested as a force acting on water molecules in a solution separated from pure water by a membrane that is permeable to water molecules only and can be expressed as the sum of the solute potential and the pressure potential: Ψ = Ψ_s + Ψ_p

Water potential is measured in kilopascals (kPa). The water potential of pure water is zero; aqueous solutions of increasing concentration have increasingly negative values. Water tends to move from areas of high (less negative) water potential to areas of low (more negative) water potential. Osmosis in plants is now described in terms of water potential. In soils and other extracellular systems, another factor, called matric potential, can contribute significantly to water potential.

water potential
1. (osmotic potential, chemical potential) The difference between the energy of water in the system being considered and of pure, free water at the same temperature. The water potential of pure water is zero, so that of a solution will be negative. If there is a gradient of water potential between two plant cells, water will diffuse down the gradient until equilibrium is reached.

2. See CAPILLARY MOISTURE.

water potential
1. (chemical potential, osmotic potential) The difference between the energy of water in the system being considered and of pure, free water at the same temperature. The water potential of pure water is zero, so that of a solution will be negative. If there is a gradient of water potential between two plant cells, water will diffuse down the gradient until equilibrium is reached.

2. See capillary moisture.

water potential The difference between the energy of water in the system being considered and of pure, free water at the same temperature. The water potential of pure water is zero, so that of a solution will be negative. If there is a gradient of water potential between two cells, water will diffuse down the gradient until equilibrium is reached.

water potential
1. A measure of the energy that causes water to enter plant cells. There is a net movement of water from a region of high water potential to one of low water potential.

2. Surface tension. See CAPILLARY MOISTURE.