Biology

Polar substances form hydrogen bonds with water molecules clustered around them.

When a polar solute is added to the solution on one side of a membrane, it reduces the number of free water molecules on that side of the membrane increasing the osmotic pressure.

Because the hypo-osmotic side of the membrane (with less solute) has more unbound H20 molecules than the hyper-osmotic side (with more solute), H2O moves by diffusion from the right to the left.