Osmosis is the flow of one element of a solution through a membrane while the other elements are blocked and not able to pass through the membrane.
Experimentation is often necessary to see which membranes would allow osmosis (selective flow). This is because not all membranes behave in the same way. Some membranes allow all or none of the elements of a solution to pass through.
n one demonstration of osmosis, a vertical tube with a solution of sugar, with its lower end closed off by a semi-permeable membrane, is placed in a container of water. As the water passes through the membrane into the tube, the level of sugar solution in the tube rises.