Water potential

the chemical potential of pure water (μ o w ) as the standard, the chemical heat of water in a system under isothermal pressure (μ w ) and the difference between that standard, divided by the hydromormal volume of water (
V
w ) is called the water potential of the system (ψ w ).。Its units are "pressure" units, usually expressed in Palestinian. Expressed as a pa (
pa
system of international units. The water potential of pure water is set at zero, and the water potential of other systems, such as aqueous solution, is negative. A water potential is defined as an export from the chemical potential of water, which is measured in energy. The direction of spontaneous processes in nature is that energy moves from higher to lower levels. Permeation can occur because there is a gradient of water's free energy on both sides of the semi-permeable membrane. Because the water potential is derived from the chemical potential promotion, the water potential is also the strength factor that promotes the movement of water. Water always flows from one side with a high water level to the other side with a low water level.。The water potential of any water-containing system is affected by factors that alter the free energy of water molecules. Mature plant cell water potential is mainly affected by cellular fluid ψ) and cellular pressure ψ p ). So generally speaking, plant cell water potential is equal to the algege of the osmosis and pressure potential, that is: ψ w

ψψp . The figure shows the change in the value of the ψ
w
the water absorption process. When in the initial mass wall separation, the cell is not tense (in relative volume of
1.0
), at this time the pressure potential is equal to zero, the water potential of the cell is equal to the permeability of the cell fluid, both of which are minimal (about
-20
bar). When it is put into pure water, cells absorb water, the volume is increasing, the cell pressure potential is also increasing, with the cell water absorption cell fluid is also slightly diluted, so the penetration potential is also slightly increased (finally about
-15
bar), the cell water potential also increased (negative absolute value tends to be smaller). When the cell absorbs water to the maximum limit (in terms of relative volume of
1.5
), the cell volume is the largest, the pressure potential is also the maximum (about
15
bar), at this time the pressure potential and the absolute value of the permeability potential is equal, then the cell water potential is equal to zero, and the external pure water potential is equal, although the cell fluid penetration is less than the water potential of the outside water, but the cell stop absorbing water. At this point the cell is at its most tense state. (bar: A unit that represents a pressure.)
1

10
-6 dauthan cm -2 , Pa: is short for
pascal
, the international unit of pressure. Mpa is commonly used in plant
and
.
1Mpa
10
6
ppa
9.87
standard atmospheric pressure. )。