Define water potential and solute potential.

Explanation

Water potential is a measure of free energy associated with water per unit volume `(JM^(-3))`. The water potential of pure water `(Psi_(w))` at atmospheric pressure is zero. The unit of water potential is bars or Pascal (1m Pa=10 bars).
solute Potential The addition of solutes reduce water potential (to a negative value). This reduces the concentration of water. Hence, solutions have a lower water potential than pure water, the magnitude of this lowering due to dissolution of a solute is called solute potential or `Psi_(s)`.