(a) Semi-permeable membrane: It is a membrane that allows the movement of solvent
molecules (e.g. water molecules) through it but prevents the movement of solute
particles (e.g. sugar or salt molecules).
For example: Egg membrane, parchment membrane, cellophane paper etc. are semi-
(b) Osmosis: The diffusion of water molecules through a semi-permeable membrane
from a region where water is more concentrated to a region where it is less
concentrated is called osmosis.
In other words, osmosis is the diffusion of water from its pure state or dilute solution into
a stronger or concentrated solution through a semi-permeable membrane.