water potential, suction pressure
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water potential, suction pressure or (formerly) diffusion pressure deficit (DPD)the tendency of a cell to draw in water from outside by OSMOSIS, the water moving from a higher to a lower water potential. Since pure water at one atmosphere has a water potential of zero, cells drawing in water have a water potential of less than zero. Thus water potential is measured as a negative value, which can be confusing. Readers should be careful when using the terms ‘higher’ or ‘lower’ water potential; ‘more negative’ or ‘less negative’ are more exact statements In mathematical terms water potential is the sum of the OSMOTIC POTENTIAL and the PRESSURE POTENTIAL of a cell:
For example, when Osmotic Potential = -9
and Pressure Potential = 4,
Water Potential = - 9 + 4 = - 5.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005