Question

Why is solute potential always negative? Explain Ψw=Ψs+Ψp

Answer 1

Water potential:

Water potential of pure water is the highest and equal to zero. This is because pure water has unbound water molecules that can move freely and therefore have high kinetic energy.


Solute potential:

• The magnitude of decrease of water potential due to the dissolution of a solute is called solute potential.
• When solute is dissolved in water, the amount of free water molecules reduces causing the kinetic energy of the molecules to reduce. Therefore the solute potential reduces. In other words it becomes negative. Therefore the solute concentration is always negative.

Ψw=Ψs+Ψp:

• Solute potential: The amount by which the water potential is reduced due to the presence of solute is called solute potential.
  • Solute potential is denoted as Ψs.
  • The solute potential decreases (gets more negative) as the concentration of solutes increases.
  • As the concentration of solutes reduces the water potential increases.
• Pressure potential: The magnitude of change of water potential due to the mechanical pressure is called Pressure potential.
  • Pressure potential is denoted as Ψp .
  • The pressure potential can be negative or positive.
  • It was previously known as turgor pressure. At atmospheric pressure the pressure potential is zero.
  • When pressure greater than atmospheric pressure is applied to pure water its water potential increases.

Water potential(Ψw) of a cell is affected by both solute and pressure potential. The relationship between them is as follows Ψw= Ψs+Ψp



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