Class 11 Biology Transport In Plants Water potential

Water potential

  • Water potential is the difference between free energy of water molecules in a pure solvent and free energy of water molecules in a solution.
  • Solute potential (Ψs) and pressure potential (Ψp) are the two main components that determine water potential.
  • The greater the concentration of water in a system, the greater is its kinetic energy or ‘water potential’.
  • Water potential is denoted by the Greek symbol Psi or Ψ and is expressed in pressure units such as pascals (Pa).
  • The water potential of pure water at standard temperatures is taken to be zero.
  • All solutions have a lower water potential than pure water; the magnitude of this lowering due to dissolution of a solute is called solute potential.
  • For a solution at atmospheric pressure (water potential) Ψw = (solute potential) Ψs.
  • The pressure exerted by the protoplasts due to entry of water against the rigid walls is called pressure potential (Ψp).
  • When water enters a plant cell due to diffusion causing a pressure built up against the cell wall, it makes the cell turgid, which increases the pressure potential.
  • Water potential of a cell is affected by both solute and pressure potential: Ψw = Ψs + Ψp


Fig. Water potential

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