Biology – Movement into and out of cells | e-Consult

Water potential is a measure of the tendency of water to move from one area to another. It's defined as the difference in water potential between pure water and a solution. Pure water has a water potential of 0. Solutions with solutes have a negative water potential. The more solutes present, the more negative the water potential.

Water moves from areas of high water potential (less negative) to areas of low water potential (more negative). This movement is driven by the tendency of water to equalize the water potential across a membrane or between different solutions. Water moves via osmosis, which is the net movement of water across a semi-permeable membrane from a region of higher water potential to a region of lower water potential.

Consider these scenarios:

• A pure water solution in contact with a solution containing solutes: Water will move from the pure water into the solution with solutes, attempting to equalize the water potential.
• A plant cell with a high solute concentration in contact with a cell with a lower solute concentration: Water will move from the cell with lower solute concentration to the plant cell, driven by the higher water potential of the lower solute concentration solution.
• A soil with a high water potential in contact with a plant root cell with a low water potential: Water will move from the soil into the root cell, driven by the higher water potential of the soil.