What is the principle behind the experiment which states Osmosis?

Question

I am 11th student.I have a doubt about the experiment which show osmosis in plants. I read that mouth of an inverted thistle funnel is covered with a semi permiable membrane and the funnel is then filled with concentrated solution and dipped in a beaker containing pure solvent. As by the principle osmosis the pure solvent will enter into the funnel through semi permiable membrane and the level of solution inside funnel rises up.This what the experiment shows but I doubts that IT IS DUE TO THE ATMOSPHERIC PRESSURE acting on the surface of pure solvent, b'coz when we dip a straw in water the level of water rises inside the straw. By the same way why should the same thing to be happend here??


please reply me immediatly to get rid of this doubt

Answer 1

When a solution and a pure solvent are separated by a semipermeable membrane the volume of the solution increases because the net movement of the solvent molecules is from the pure solvent to the solution. The liquid in the tube above the solution slowly rises. If the membrane is strong enough to withstand the pressure and if the tube is long enoughj the liquid will rise until its hydrostatic pressure is great enough to prevent further osmosis of solvent molecules into the solution.