While diffusion deals with the movement of particles of solid, liquid and gas, Osmosis deals with the movement of only the particles of a solvent (liquid). We will study osmosis with the help of an experiment. Take a beaker which is half filled with water.
Take a thistle funnel and tie its mouth with the help of parchment paper, sheep bladder or egg membrane. These membranes are called selectively permeable or differentially permeable, since they allow only certain particles to pass through and not all. In this case the selectively permeable membrane is permeable to only molecules of water but impermeable to others.
Fix the thistle funnel to a stand and immerse it in the water contained in the beaker. Fill the thistle funnel with 5% sugar solution and note the level. After some time it may be observed that the level of the sugar solution in the thistle funnel rises. Why? Water from the beaker must have entered into the thistle funnel.
Now taste the water in the beaker. It does not taste sweet, because the membrane has allowed only the water molecules to enter into the thistle funnel but has not allowed the sugar molecules into the beaker.
ADVERTISEMENTS:
Water migrates into the thistle funnel because it is in higher concentration in the beaker. Hence Osmosis may be defined as the movement of the molecules of a solvent (water) from the region of their higher concentration through a selectively permeable membrane. In this, there will be no movement of the solute particles.