Osmosis is a vital process in biological systems, as biological membranes are semipermeable. In general, these membranes are impermeable to large and polar molecules, such as ions, proteins, and polysaccharides, while being permeable to non-polar or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or organelle membranes by diffusing across the phospholipid bilayer via aquaporins (small transmembrane proteins similar to those responsible for facilitated diffusion and ion channels). Osmosis provides the primary means by which water is transported into and out of cells. The turgor pressure of a cell is largely maintained by osmosis across the cell membrane between the cell interior and its relatively hypotonic environment.
Osmosis is the movement of a solvent across a semipermeable membrane toward a higher concentration of solute. In biological systems, the solvent is typically water, but osmosis can occur in other liquids, supercritical liquids, and even gases.[12][13]
The mechanism responsible for driving osmosis has commonly been represented in biology and chemistry texts as either the dilution of water by solute (resulting in lower concentration of water on the higher solute concentration side of the membrane and therefore a diffusion of water along a concentration gradient) or by a solute's attraction to water (resulting in less free water on the higher solute concentration side of the membrane and therefore net movement of water toward the solute). Both of these notions have been conclusively refuted.
It is difficult to describe osmosis without a mechanical or thermodynamic explanation, but essentially there is an interaction between the solute and water that counteracts the pressure that otherwise free solute molecules would exert. One fact to take note of is that heat from the surroundings is able to be converted into mechanical energy (water rising).
Osmosis is responsible for the ability of plant roots to draw water from the soil. Plants concentrate solutes in their root cells by active transport, and water enters the roots by osmosis. Osmosis is also responsible for controlling the movement of guard cells.
Osmosis also plays a vital role in human cells by facilitating the movement of water across cell membranes. This process is crucial for maintaining proper cell hydration, as cells can be sensitive to dehydration or overhydration. In human cells, osmosis is essential for maintaining the balance of water and solutes, ensuring optimal cellular function. Imbalances in osmotic pressure can lead to cellular dysfunction, highlighting the importance of osmosis in sustaining the health and integrity of human cells.
In unusual environments, osmosis can be very harmful to organisms. For example, freshwater and saltwater aquarium fish placed in water of a different salinity than that to which they are adapted to will die quickly, and in the case of saltwater fish, dramatically. Another example of a harmful osmotic effect is the use of table salt to kill leeches and slugs.
Reverse osmosis is a separation process that uses pressure to force a solvent through a semi-permeable membrane that retains the solute on one side and allows the pure solvent to pass to the other side, forcing it from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This process is known primarily for its role in turning seawater into drinking water, when salt and other unwanted substances are ridded from the water molecules.[16]
Osmosis may be used directly to achieve separation of water from a solution containing unwanted solutes. A "draw" solution of higher osmotic pressure than the feed solution is used to induce a net flow of water through a semi-permeable membrane, such that the feed solution becomes concentrated as the draw solution becomes dilute. The diluted draw solution may then be used directly (as with an ingestible solute like glucose), or sent to a secondary separation process for the removal of the draw solute. This secondary separation can be more efficient than a reverse osmosis process would be alone, depending on the draw solute used and the feedwater treated. Forward osmosis is an area of ongoing research, focusing on applications in desalination, water purification, water treatment, food processing, and other areas of study.
Future developments in osmosis and osmosis research hold promise for a range of applications. Researchers are exploring advanced materials for more efficient osmotic processes, leading to improved water desalination and purification technologies. Additionally, the integration of osmotic power generation, where the osmotic pressure difference between saltwater and freshwater is harnessed for energy, presents a sustainable and renewable energy source with significant potential. Furthermore, the field of medical research is looking at innovative drug delivery systems that utilize osmotic principles, offering precise and controlled administration of medications within the body. As technology and understanding in this field continue to evolve, the applications of osmosis are expected to expand, addressing various global challenges in water sustainability, energy generation, and healthcare.[17]
Details on osmosis development are available at Osmosis/Development. Visit there for documentation on the internal structure of osmosis, design decisions, steps to configuring development environments, etc.
In physiology, osmosis (Greek for push) is the net movement of water across a semipermeable membrane. Across this membrane, water will tend to move from an area of high concentration to an area of low concentration. It is important to emphasize that ideal osmosis requires only the movement of pure water across the membrane without any movement of solute particles across the semipermeable membrane. Osmosis can still occur with some permeability of solute particles, but the osmotic effect becomes reduced with greater solute permeability across the semipermeable membrane. It is also true that, at a specific moment in time, water molecules can move towards either the higher or lower concentration solutions, but the net movement of water will be towards the higher solute concentration. The compartment with the highest solute and lowest water concentration has the greatest osmotic pressure. Osmotic pressure can be calculated with the van 't Hoff equation, which states that osmotic pressure depends on the number of solute particles, temperature, and how well a solute particle can move across a membrane. Its measured osmolality can describe the osmotic pressure of a solution. The osmolality of a solution describes how many particles are dissolved in the solution. The reflection coefficient of a semipermeable membrane describes how well solutes permeate the membrane. This coefficient ranges from 0 to 1. A reflection coefficient of 1 means a solute is impermeable. A reflection coefficient of 0 means a solute can freely permeable, and the solute can no generate osmotic pressure across the membrane. The compartment with the greatest osmotic pressure will pull water in and tend to equalize the solute concentration difference between the compartments. The physical driving force of osmosis is the increase in entropy generated by the movement of free water molecules. There is also thought that the interaction of solute particles with membrane pores is involved in generating a negative pressure, which is the osmotic pressure driving the flow of water. Reverse osmosis occurs when water is forced to flow in the opposite direction. In reverse osmosis, water flows into the compartment with lower osmotic pressure and higher water concentration. This flow is only possible with the application of an external force to the system. Reverse osmosis is commonly used to purify drinking water and requires the input of energy. The concept of osmosis should not be confused with diffusion. Diffusion is the net movement of particles from an area of high to low concentration. One can think of osmosis as a specific type of diffusion. Both osmosis and diffusion are passive processes and involve the movement of particles from an area of high to low concentration.
While diffusion is often depicted as the net movement of solutes between two solutions, osmosis is about the net movement of the solvent molecules (not the solute) (solvent such as water molecules). The differing concentration of water molecules between the two sides of the membrane is what drives the water to move so as to equalize the concentrations of the two areas.
In biology, osmosis is defined as the net movement of water molecules through a biological membrane (e.g. cell membrane) from an area of higher to an area of lower water potential. Other definitions of osmosis are as follows:
In chemistry, osmosis is defined similarly. It is the passage of a pure solvent from a solution of lesser to one of greater concentration of solutes when the two solutions are separated by a membrane that selectively prevents the passage of solute molecules while allowing the solvent molecules to pass through.
Etymology: The term osmosis is a Latinized form of now obsolete osmose. A derived word is osmotic, which is defined as pertaining to or of the nature of osmosis. Thus, osmotic pressure, for instance, is a pressure that arises due to or is relevant to osmosis.
Water molecules tend to move, and they move downhill, i.e. from an area of high water concentration (or fewer solutes) to an area of low water concentration (or greater solutes). If there is no net movement of water, it cannot be called osmosis. It should also incorporate a semipermeable membrane to move across. Without it, the process is only a case of diffusion and not osmosis.
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