The basic process of a cell of how things move into or out of the cell through the cell membrane is called cell transport and osmosis is a type of passive transport i.e., transport without the use of energy.
Osmosis definition:
“It is the random net flow of solvent molecules over a semipermeable barrier from a low solute concentration to a high solute concentration until equilibrium is attained.”
Osmosis is an important mechanism in biological systems as the biological membranes are semipermeable i.e., partially permeable. Large and polar molecules, such as ions, enzymes, proteins and polysaccharides, cannot pass through these membranes. Osmosis is considered as the major method for transporting water into and out of cells.
Although water is the most common solvent in biological systems, osmosis can also occur in other liquids, and even gases. Water molecules move across the cell membrane from an area of low solute concentration to a high solute concentration area when a cell is submerged in water. For example, when a cell is immersed in saltwater, water molecules leave the cell. Water molecules move into a cell when it is submerged in freshwater.
Osmosis is not associated with uptake of minerals and nutrients.
As water enters the cell, the turgor pressure exerted against the cell wall rises up, until it reaches an equilibrium state, thus equals the osmotic pressure as well.
When a cell is present in hypertonic (more concentrated than its own) solution:
Water moves out of the cell and the cell shrinks when it is placed in a solution that is hypertonic compared to the cytoplasm. The cell becomes flaccid as a result of this. The cell becomes plasmolysed in extreme circumstances, when the cell membrane disengages from the cell wall due to a loss of water pressure.
When a cell is immersed in hypotonic (less concentrated than its own) solution:
When it is placed in a solution that is hypotonic to its cytoplasm, water moves into a plant cell and causes the cell to swell and become turgid.
When a cell is placed in Isotonic (concentration is same as its own) solution:
There will be no net movement of water across the cell membrane if the medium is isotonic.
This means that if a cell is put in a solution with a higher solute concentration than its own, it will shrivel, and if it is put in a solution with a lower solute concentration than itself, it will swell and may possibly burst.
Examples of Osmosis:
- The absorption of water molecules from the soil through the roots of the plant.
- Osmosis is also responsible for controlling guard cell movement.
- When your fingers are submerged in water for a long period of time, they become pruned.
- Germination of seeds is due to osmosis.
- Osmosis helps in the absorption of water from the intestines into the bloodstream.
- Plants are more resistant to drought injury when their osmotic pressure is higher.
- Toxic metabolic waste products, such as urea, are released.
- Osmosis can be extremely harmful to species in unusual situations. , for example, Freshwater and saltwater aquarium fish will die rapidly and drastically if placed in water with a different salinity than that to which they were adapted. The use of table salt to kill leeches and slugs is another example of a harmful osmotic impact.
Reverse osmosis:
Reverse osmosis is a process of separation in which a solvent is forced to move through a semipermeable membrane that retains the solute on one side while the pure solvent is allowed to pass through on the other side, i.e., it moves from a region of high solute concentration to a region of low solute concentration by applying a pressure greater than the osmotic pressure. To reverse the osmosis process, you must overcome the osmotic pressure balance across the membrane because the flow is normally from dilute to concentrated.
Pressure retarded osmosis:
PRO (pressure retarded osmosis) is a technique used to separate a solvent (for example, fresh water) from a more concentrated (for example, sea water) and pressurized solution. Osmosis permits the solvent to pass through a semipermeable membrane to the concentrated solution side. The salinity gradient energy resulting from the difference in salt concentration between sea and river water can be used to create power using this technology.