Question

What is the difference between water potential and osmotic potential?

Answer 1

Hint: The difference between water potential and osmotic potential depends upon the terms osmotic pressure, turgor pressure and diffusion pressure deficit. Osmotic pressure is the maximum turgor pressure that can develop in a cell. Turgor pressure is the actual pressure developed in a cell at a given time. The difference between osmotic pressure and turgor pressure is the diffusion pressure deficit.

Complete answer:

S.No.	Water potential	Osmotic potential
1.	Water potential is the measure of concentration of free water molecules, I.e., potential energy of the cell.	Osmotic potential is a measure of movement of water molecules from a region of lower solute concentration to higher solute concentration.
2.	The movement of free water molecules is zero for pure water and negative for cells containing solutes.	Osmotic potential decreases with increase in solute concentration (since water molecules will be less free to move due to more solute molecules).
3.	Water potential is the reduction in free energy of solvent in a system over its pure state.	It is a reduction in free energy of water due to a decrease in the number of water molecules per molal volume.

Note:
Water potential is represented by Greek letter Psi (Ψ) and is always less than zero or has negative values. It is equal but opposite in sign to the diffusion pressure deficit (D.P.D.). If a difference in water potential exists between two regions, the spontaneous downhill movement of water will take place, i.e., from the region of higher water potential to the region of lower water potential. Osmotic potential develops in both confined as well as in unconfined systems. The value is negative, though it is numerically equal to osmotic pressure.