Question

Define the term water potential. What are its components? Explain.

Answer 1

Water potentialis defined as the difference between chemical potential of water at any point in a system and that of pure water under standard conditions. It is designated by sign Psi (ψ).

There are three major components of water potential in a plant cell. These are: (a) Matrix potential, (b) Solute potential and (c) Pressure potential.

Matrix potential (ψ${}_m$) is the component of water potential which is determined by the attraction between hydrated colloidal molecules, cell wall etc., and water.

Solute potential (ψ${}_s$) is also known as the osmotic potential. It may be defined as the amount by which water potential is always represented in negative numbers.

Pressure potential (ψp) is represented by the cell wall and cell membrane. The cell wall exerts a pressure (WP) on the cell contents. Similarly the cell membrane also exerts a pressure (ψ${}_p$) on the cell wall by virtue of its solvent content. The pressure potential is positive.

ψ=ψ${}_m$+ψ${}_s$+ψ${}_p$