Factors Affecting Water Potential

Water potential (Ψ) is a measure of the potential energy of water to do work. To do work, an object must be able to exert enough force to move another object. For water to move an object, it must be in motion. When atmospheric pressure is applied to a given volume of water, the highest water potential it can have is 0. This is the water potential of distilled water, which has the highest potential to move and displace objects.

Solute potential (Ψs), also known as osmotic potential, is negative in plant cells and is zero in distilled water. When solutes are added to water, they reduce the water potential due to the intake of potential energy that is available in the water. This decrease in water potential is known as the solute potential. Hydrophilic molecules, which can associate with water through hydrogen bonds, are able to dissolve in water, while hydrophobic molecules, such as oil, cannot. Therefore, when the solute potential decreases, the solute concentration increases.

Water moves from the soil into the root cells of the plants through osmosis due to the difference in the water potential, which is sometimes referred to as osmotic potential.

Factors affecting Water potential and Solute potential

Factors Affecting Water Potential

The sum of the pressure, concentration, and gravity components of water potential in plants is:

Ψ = Ψs + Ψp + Ψg

Ψs denotes the effects of solutes, Ψp denotes the effects of pressure, and Ψg denotes the effects of gravity on the free energy of water.

The Impact of Solutes on Water Potential

The solute potential or the osmotic potential indicates the effect of the dissolved solutes on water potential. The solutes reduce the free energy of water by the dilution of water, which mainly is an entropy effect. In other words, combining solutes and water causes an increase in the entropy or disorder of the system and hence decreases the free energy. This indicates that the osmotic potential is independent of the particular nature of the solute.

The Influence of Pressure on Water Potential

The pressure potential is the effect of hydrostatic pressure on water’s free energy. A positive pressure increases the water potential, while a negative pressure decreases it. Both negative and positive pressure occur in plants. In the cells, the positive hydrostatic pressure is known as turgor pressure. The negative hydrostatic pressure that develops in the xylem conduits is often referred to as tension.

The Influence of Gravity on Water Potential

Gravitational potential $= mgh + \frac{1}{2} \rho gh^2$

Ψg = 0.01 MPa m-1

The gravitational factor (Ψg ) is typically disregarded when examining water transport at the cellular level, as differences in this factor among neighboring cells are insignificant in comparison to variations in pressure potential and osmotic potential.

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