Osmosis is the physical process by which solvent molecules form the region of lower concentration diffuse into the solution of higher concentration through a semi-permeable membrane when a solution and solvent is separated by a semi-permeable membrane.
In Osmosis movement of molecules takes place from the area of high potential (pure solvent or low concentrate solution) to the area of lower potential(higher concentrated solution) when both are separated by semi-permeable membrane. Movement of molecules continues till equilibrium in concentration is attained. This potentially is called Osmotic potential.
The pressure which developed due to difference in concentrations on the membrane is called osmotic pressure. Osmotic pressure is defined as the pressure which developed in a solution to increase its Chemical Potential.
Based on Gibb’s free energy relationship Osmotic potential is designated with negative sign. Thus a molar sucrose solution at 00C has an Osmotic potential of -22.4 atm. Or -22.7 bars.
Dutch chemist Vant Hoff formulated an equation to measure the Osmotic potential i.e.-
Where π is the Osmotic Potential, ‘C’ is the concentration of the solution and ‘R’ is the gas constant (0.0820 litre. atm degree mole) and ‘T’ is the temperature (273-00C)
Here C= No of Moles (N)
Volume in liters (V)
Plant cells act as osmotic systems due to presence of semi-permeable plasma membrane which separate cell sap solution from the external solution.
Significance of Osmosis in Plants:-
i) Water is absorbed by root from soil by osmosis.
ii) Distribution of water takes place through plant tissues by osmosis.
iii) It helps in transpiration and guttation.
iv) High osmotic pressure out side the sell sap cause plasmolysis.
v) Osmosis maintains water restoration and turgidity of plant cells and organs.
vi) High osmotic Concentration help in resisting draught and frost.
vii) It also regulates various movements in plants.