Explanation

Diffusion of water from its pure state or dilute solution into a solution or stronger solution, when the two are separated by semi-permeable membrane is called osmosis. In thistle funnel experiment, when sugar solution is added to beaker after the process of osmosis stops, the solution of beaker becomes hypertonic, as a result of which exosmosis occurs in thistle funnel hence, level of solution in thistle funnel lowers.