THE CONCEPT OF WATER POTENTIAL ( )
The free energy is the thermodynamic parameter that determines
the direction in which physical and chemical changes must occur
(Free energy is the sum of an energy of a system capable of doing
work). The difference between the free energy of water molecules
in pure water and that of water in any other system (e.g., water in a
solution or in a plant cell or tissue) is termed as water potential.
The Greek letter psi, the symbol for which is y designates the water
potential in a system. The water potential is measured in bars;
The water potential of a solution can be determined using pure
water as the standard of reference. The pure water, at atmospheric
pressure, has a water potential of zero (0).
The presence of solute particles reduces the free energy of water
and thus decreases the water potential (negative value). I t is
therefore, the water potential of a solution is always less than zero.
The direction of flow will be from the region of higher water
potential (as in pure water) to the region of lower water potential
(as in a solution. The movement of water continues until the water
potential of the two regions becomes equal. At this point of
equilibrium, net transfer of water will cease.
, THE COMPONENTS OF WATER POTENTIAL
For solutions, such as contents of cells, water potential is determined by
three major sets of internal factors viz, matric potential ( m), solute
potential ( s) and pressure potential (p ). The water potential ( ) in
a plant cell or tissue can be written as the sum of the matric potential
(m ) due to binding of water to cell walls and cytoplasm, the solute
potential ( s) due to concentration of dissolved solutes, which by its
effect on the entropy components reduces the water potential and the
pressure potential ( p) due to hydrostatic pressure. which by its effect
on the energy components increases the water potential:
Each component potential is discussed separately below:
Matric potential ( m):
Matric is the term used for a surface of hydrophilic colloids (such as clay
particles, cell wall polysaccharides, proteins, starch, etc.) to which the
The free energy is the thermodynamic parameter that determines
the direction in which physical and chemical changes must occur
(Free energy is the sum of an energy of a system capable of doing
work). The difference between the free energy of water molecules
in pure water and that of water in any other system (e.g., water in a
solution or in a plant cell or tissue) is termed as water potential.
The Greek letter psi, the symbol for which is y designates the water
potential in a system. The water potential is measured in bars;
The water potential of a solution can be determined using pure
water as the standard of reference. The pure water, at atmospheric
pressure, has a water potential of zero (0).
The presence of solute particles reduces the free energy of water
and thus decreases the water potential (negative value). I t is
therefore, the water potential of a solution is always less than zero.
The direction of flow will be from the region of higher water
potential (as in pure water) to the region of lower water potential
(as in a solution. The movement of water continues until the water
potential of the two regions becomes equal. At this point of
equilibrium, net transfer of water will cease.
, THE COMPONENTS OF WATER POTENTIAL
For solutions, such as contents of cells, water potential is determined by
three major sets of internal factors viz, matric potential ( m), solute
potential ( s) and pressure potential (p ). The water potential ( ) in
a plant cell or tissue can be written as the sum of the matric potential
(m ) due to binding of water to cell walls and cytoplasm, the solute
potential ( s) due to concentration of dissolved solutes, which by its
effect on the entropy components reduces the water potential and the
pressure potential ( p) due to hydrostatic pressure. which by its effect
on the energy components increases the water potential:
Each component potential is discussed separately below:
Matric potential ( m):
Matric is the term used for a surface of hydrophilic colloids (such as clay
particles, cell wall polysaccharides, proteins, starch, etc.) to which the
