Osmosis is movement of a solvent (such as water) across a semipermeable membrane into areas of higher solute concentration. Osmotic pressure determines the quantity of water displaced; it is proportional to the number of solute particles in a give volume of solution.
The tendency of water to move by osmosis is expressed as water potental, the Greek letter psi is used as its symbol and it is measured in kPa (kiloPascals). Pure water has a water potential of 0kPa, solutes lower the water potential.
- Wile, Dr. Jay L. Exploring Creation With Biology. Apologia Educational Ministries, Inc. 1998