The diffusion of water molecules through a semi-permeable membrane from a region of its higher concentration (more dilute solution) to its lower concentration (less diluted solution) is called osmosis.
In other words, osmosis is the diffusion of water from its pure state or a dilute solution into a stronger or concentrated solution through a semi-permeable membrane.
Osmotic Pressure:
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The results of the above activities show that the pressure builds up in the sugar solution and forces the solution up the capillary tube. The pressure results from the rapid diffusion of water molecules from the dilute to the more concentrated solution.
The osmotic pressure is the maximum pressure which can develop in an osmotically active solution when it is separated by a semi-permeable membrane to stop further endosmosis from a region of lower concentration to a higher concentration of solute. Osmotic pressure can also be defined as the pressure required to completely stop the entry of water into a solution across a semi-permeable membrane.
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Osmotic Potential:
The osmotic potential of a solution is a measure of the tendency of water molecules to diffuse out of it. A concentrated solution that has relatively few water molecules has a low osmotic potential. On the other hand, a dilute solution with a larger proportion of water molecules has a high osmotic potential. Pure water has the highest possible osmotic potential.
Movement of water in a plant occurs from a dilute solution of a high osmotic potential to a concentrated solution of a low osmotic potential.