Region A has a low solute concentration, while Region B has a high solute concentration. A selectively permeable membrane, which is impermeable to the solute but allows water to pass through, separates them.

When we have two regions, A and B, separated by a selectively permeable membrane, and region A has a low solute concentration while region B has a high solute concentration, we can expect a process called osmosis to occur.

• Osmosis is the movement of water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. The purpose of this movement is to equalize solute concentrations on both sides of the membrane.
• Since the membrane is impermeable to the solute, the solute particles cannot move across to balance the concentration difference. Hence, water, which can move freely through the membrane, will move from region A (where there's less solute and more water) into region B (where there's more solute and less water). This process will continue until the solute concentration on both sides of the membrane is balanced or the hydrostatic pressure (caused by the volume of water moving to region B) counteracts the osmotic pressure, bringing the system into equilibrium.