The semi permeable membrane is very important in the phenomenon of osmosis because they only permit the movement of solvent molecules through them.
Two solutions having similar osmotic pressure at a given temperature are called isotonic solutions. If the given solution has less osmotic pressure it is called hypo tonic and it is hyper tonic if its osmotic pressure is higher than the solution on the other side of semi permeable membrane.
Osmosis takes place only in hypo tonic and hypertonic solutions.
