Question

What are the parameters which control water potential?

Answer 1

1. Slatyer and Taylor (1960) introduced the concept of water potential.
   Definition - water potential is the potential energy of water in a system - compared to pure water when temperature and pressure are kept constant.
2. It is also a measure of how freely water molecules can move in a particular environment or system. Water potential is denoted by the Greek symbol Ψ (psi) and measured in Pascal (Pa). At standard temperature, the water potential of pure water is zero
3. Addition of solute to pure water decreases the kinetic energy thereby decreasing the water potential, from zero to negative.
4. So, Comparatively a solution always has low water potential than pure water. In a group of cells with different water potential, a water potential gradient is generated.
5. Water will move from higher water potential to lower water potential.
   When potential (Ψ) can be determined by. Solute concentration or Solute potential (Ψ_s) Pressure potential (Ψ_p)
   By correlating two factors, water potential is written as (Ψw=Ψ_s)+Ψ_p

• Solute potential (Ψ_s) or Osmotic potential -

1. Denotes the effect of dissolved solute on water potential.
2. In pure water, the addition of solute reduces its free energy and lowers the water potential value from zero to negative.
3. Thus the value of solute potential is always negative. In a solution at standard atmospheric pressure, water potential is always equal to solute potential (Ψw = Ψ_s).

• Pressure Potential (Ψ_p) -

1. Pressure potential is a mechanical force working against the effect of solute potential.
2. Increased pressure potential will increase water potential and water enters cells and cells become turgid.
3. This positive hydrostatic pressure within the cell is called Turgor, pressure likewise, withdrawal of water from the cell decreases the water potential and the cell becomes flaccid.