Question

Define and explain water potential

Answer 1

The difference of free energy present in the water of a system when compared with the free energy of pure water at constant temperature and pressure is called water potential. The concept of water potential was first given by Slatyer and Taylor. It is based on the on two important principles free energy and chemical potential. Water potential works on the laws of thermodynamics.

The symbol of water potential is ᴪ(psi). It is a relative measure and water potential of pure water is arbitrarily set at zero. So, the water potential of a solution is always expressed in negative values. It is always measured in Megapascals.

In plants, water potential is influenced by three components, osmotic potential, pressure potential, and matric potential.

Osmotic potential: The amount of water get lowered in a solution by the addition of solutes is called Osmotic potential.

The symbol of osmotic potential is (ᴪ_π-). It is always showing a negative value.

Pressure potential: The amount of water potential increases after the addition of water in a cell is called Pressure potential. The symbol of pressure potential is (ᴪ_p). It always shows a positive value.

Matric potential: The amount or quantum of decrease of water potential in a solution on account of matric forces is called Matric potential.

It is represented by a symbol tau.

it always has negative value.

The relation between water potential, osmotic potential and pressure potential is ᴪw= ᴪ_π +ᴪ_p +ᴪ_t

but in living cells matric potential is negligible.

So, water potential is calculated as the sum of the osmotic potential and pressure potential. ᴪ_w = ᴪ_π +ᴪ_p

Importance of water potential:

It regulates the direction of movement of water in plants.

In plants, water always move from high water potential region to low water potential region.