Question

A perfect partition between the osmotically active system and pure water in physical
conditions can be formed by a
A. Semipermeable membrane
B. Impermeable membrane
C. Freely permeable membrane
D. None of these

Answer 1

Osmosis is a net movement of solvent molecules through a selectively or semi permeable membrane into a region of high solute concentration to the low solute concentration to equalize the solute concentration on both sides.

Complete answer:
● There is an osmotically active system containing osmotically active solutes and on the other side of the membrane, there is pure water.
● Impermeable membranes are those which do not allow any molecule to pass through. So, there will be increased water potential on one side with decreased water potential on the other side and no equilibrium will be there.
● Freely permeable membranes are those which allow both solutes and solvents to pass through.
● But in osmosis, only solvent molecules pass through the membrane.
● On the osmotically active side, there is low water potential and on the other side, there is high water potential.
● So, to attain equilibrium (equalize water potential), one side has to increase its water potential while others have to decrease its water potential.
● The only way to achieve is the movement of a solvent molecule from pure water towards osmotically active solute is through the barrier.
● The type of membrane which allows the only solvent molecule to pass through without the involvement of a solute molecule is called a Semi permeable membrane.
So, the correct option is (A) Semipermeable membrane.

Note: Difference in the water potential determines the gradient of flow. The natural tendency of water is to move towards osmotically active solute which has low water potential. Water potential becomes equal by attaining the equilibrium through diffusion.