Transport in Plants

| 167

Å DËMØÑSTRÅTÏØÑ ØF ØSMØSÏS

A thistle funnel filled with

sucrose solution is kept

inverted in a beaker

containing pure water.

Sucrose solution is separated

from water by a semi-

permeable membrane (e.g.

egg shell membrane).

Water moves into the funnel. As a result,

the level of the solution in the funnel rises. It

continues till the equilibrium is reached.

If an external pressure is applied from

the upper part of the funnel, no water

diffuses into the funnel through the

membrane.

This pressure required to prevent water from diffusing is the

osmotic pressure. This is the function of the solute concentration.

More the solute concentration, greater will be the pressure required

to prevent water diffusion.

Numerically, osmotic pressure is equivalent to the

osmotic potential, but the sign is opposite. Osmotic

pressure is the positive pressure, while osmotic

potential is negative.