What is the difference between water potential and osmotic potential?
1 Answer
The difference between water potential and osmotic potential can be easily understood by their correlation with traditional terms like osmotic pressure, turgor pressure and diffusion pressure deficit.
Explanation:
The differnce between water potential and osmotic potential can be easily understood by studying water relations of a cell in old terminology of turgor pressure (T.P.), osmotic pressure (O.P.) and diffusion pressure deficit (D.P.D.).
Turgpr pressure may be defined as the actual pressure developed in a cell at a given time. It varies with the passage of time.
Osmotic pressure is the maximum turgor pressure that can be developed in a cell and depends upon the concentration of solutes in cell sap. It is a constant entity for a particcular cell.
Diffusion pressure deficit is the difference between osmotic pressure and turgor pressure. The movement of water from one cell to the other is controlled by the difference in D.P.D of the two cells. Water moves from a cell having lower D.P.D. to the cell having higher D.P.D.
Water potential is modern term for D.P.D. It has the same value but is negative, whereas D.P.D. is positive. For example if the D.P.D. of a cell is 16 atmosphere, water potential of cell will be
-16 bars.
Water potential of pure water is zero. It decrease by the addition of solute and thus has negative value
Osmotic potential is similarly the modern term for osmotic pressure having same value but is negative, while O.P.is positive. For example if the O.P. of cell is 24 atmosphere, its osmotic potential will be -24 bars.
Water moves from a cell with higher water potential to a cell with lower water potential.
The relation beteen O.P. , T.P. and D.P.D. are shown by the following equation:
D.P.D. = O.P.-T.P.
Or –D.P.D. = -O.P. + T.P.
Or Water potential = Osmotic potential+ Pressure potential
Pressure potential is the same as T.P. and both have positive value.
