From Costanzo's Physiology:
Osmosis of water is not diffusion of water: Osmosis occurs because of a pressure difference, whereas diffusion occurs because of a concentration (or activity) difference of water.
Also from Costanzo, describing two solutions 1, and 2 , seprated by a semipermeable membrane, and 1 having a higher concentration of solute:
The solute in Solution 1 produces an osmotic pressure and causes, by the interaction of solutes with pores in the membrane a reduction in hydrostatic pressure of Solution 1. The resulting hydrostatic pressure difference across the membrane then causes water to flow from Solution 2 into Solution 1.
My question is:
How does the solute produce an osomtic pressure, and what type of interactions with the membrane pores causes the reduction in hydrostatic pressure that ultimately drive water movement?