When two solutions are isotonic, their osmotic potentials are equivalent and there is no net movement of water molecules. When different, hypotonic (dilute solution, fewer solutes more water) solutions have higher osmotic potential (less negative), whereas hypertonic (concentrated solution, more solutes less water) solutions have lower osmotic potential (more negative). Water molecules will flow from a hypotonic to a hypertonic solution due to differences in osmotic potentials.
Students can become perplexed while thinking about osmosis and osmotic pressure because, according to popular belief, water does not flow during osmosis from regions of higher osmotic pressure to regions of lower pressure. Rather, water diffuses from regions of increased solvent activity to regions of lower activity, causing pressure to be created. Not the other way around! Plant scientists reduce conceptual confusion by viewing osmosis in a different light.
Osmotic Potential
When water goes from one compartment to another in our simulations, it conducts work and hence contains potential energy. Plant scientists use the word water potential (psi) to represent this energy, and they define osmosis as the transfer of water from regions of higher potential (activity) to regions of lower potential (inactivity) (activity). When the water potentials of two compartments are equal, they are said to be in equilibrium.
According to the convention, the water potential of distilled water is zero, and it grows increasingly negative as solutions become more concentrated. Thus, net water diffusion happens from less negative potential regions to more negative (or lower) potential regions and continues until the potentials are equal. Many people are less confused by this technique of picturing osmosis since water potential is more strongly tied to water behaviour than the concept of pressure. As a result, we’ve also incorporated this thermodynamic understanding of water activity and potential energy in our presentation.
Solute potential (s), commonly known as osmotic potential, is negative in plant cells and 0 in distilled water. –0.5 to –1.0 MPa is a typical value for cell cytoplasm. Solutes diminish water potential (resulting in a negative w) by consuming some of the potential energy in the water. Solute molecules can dissolve in water because water molecules can bind to them via hydrogen bonds; a hydrophobic molecule, such as oil, cannot dissolve because it cannot bind to water. Because the energy in the hydrogen bonds between solute molecules and water is locked up in the bond, it is no longer available to accomplish work in the system. In other words, adding solutes to an aqueous system reduces the quantity of available potential energy. As a result, s decreases with increasing solute concentration.
Because s is one of the four components of a system or total, drop-ins will result in a decrease in total. Water flows towards places with lowers (and consequently lower total). The semipermeable membrane that divides the two sides of the tube allows water but not solutes to pass. On the right side of the first tube, solute has been added. Adding solute to the right side reduces s, forcing water to migrate to the right side of the tube. As a result, the water level is greater on the right side.
As a result, s decreases with increasing solute concentration. Because s is one of the four components of a system or total, drop-ins will result in a decrease in total. Because of the large solute concentration in the cytoplasm, the internal water potential of a plant cell is more negative than pure water. Because of this difference in water potential, water will transfer from the soil into the root cells of a plant via the process of osmosis. This is why solute potential is often referred to as osmotic potential.
Conclusion:
However, osmotic pressure is still a useful concept, especially when the differential movement of water is related to other hydraulic phenomena such as arteriole pressure (in kidney physiology) and the use of reverse osmosis for desalinating seawater, which uses hydraulic pressure to “create” distilled water from a saline solution through a selectively permeable membrane. Solute potential (s), commonly known as osmotic potential, is negative in plant cells and 0 in distilled water. –0.5 to –1.0 MPa is a typical value for cell cytoplasm. Solutes diminish water potential (resulting in a negative w) by consuming some of the potential energy in the water. Solute molecules can dissolve in water because water molecules can bind to them via hydrogen bonds; a hydrophobic molecule, such as oil, cannot dissolve because it cannot bind to water. Because the energy in the hydrogen bonds between solute molecules and water is locked up in the bond, it is no longer available to accomplish work in the system. In other words, adding solutes to an aqueous system reduces the quantity of available potential energy.