An Introduction to Osmosis: Process, Mechanisms, Exosmosis and Endosmosis
Before understanding the difference between endosmosis and exosmosis, one must be aware of the process of osmosis and its mechanism.
Definition of Osmosis
Osmosis is the flow of any solvent across a selectively permeable membrane into a region of higher solute concentration. It will result in an equilibration of the solute concentration both sides of the membrane. Although osmosis may occur in any solvent including supercritical liquids and some gases, most osmosis research involves water passing through a cell. Controlling solute concentrations and osmosis therefore manages the movement of water throughout our entire body. The water absorbed or dispersed gives stability and functionality to every cell, tissue, and organ in our body.
Mechanism of Osmosis
The base concept of osmosis is the difference in chemical potential between two components separated by a semipermeable membrane. Chemical potential is defined as the free energy accessible per mole of material in solution. In the demonstration of osmosis, the pure solvent has greater energy than that of the solution, which has lesser energy i.e., lesser chemical potential thereby creating a gradient so that the pure solvent is allowed to enter Chamber. Origin of the potential difference takes place from cytoplasmic solute involved in energy metabolism and dynamically replenishes chemical molecules.
What is Endosmosis and Exosmosis?
Endosmosis
In the endosmosis process, water diffuses in from the outside, outer side of the cell into its cytoplasm. You may study endosmosis by keeping a cell in the hypotonic solution.
A higher concentration of solutes exists inside the cells than outside in hypotonic solution. Still, based on the osmotic principle, only water molecules can diffuse through the selective barrier, not solutes. Therefore, a selective barrier will allow the water from the region surrounding the cell where it is highly concentrated into the cytoplasm. Endosmosis leads to the swelling of the cell, becoming turgid, or even bursting.
Conditions for Endosmosis
The concentration of the solute and solvent within and outside the cell during endosmosis is as follow:
- The concentration of solvent is higher and that of solute is lower outside the cell than within.
- In comparison to the cell’s surrounding, the cytoplasm has higher solute and lower solvent concentration.
Exosmosis
It is the osmosis type wherein the direction of water or solvent is away from a vessel or cell. It does happen in the existence of different water potential inside and outside cells. In consequence, the concentration in the solution outside the cell surpasses the same solute concentration in the cytoplasm. Exocytosis is the process during which water leaves the cell by diffusion out of the semipermeable cell membrane. This leads to the contraction of cells and plasmolysis.
Conditions for Exosmosis
The concentration of the solute and solvent within and outside the cell during endosmosis is as follow:
- The concentration of solvent is lower and that of solute is higher outside the cell than within.
- In comparison to the cell’s surroundings, the cytoplasm has lower solute and higher solvent concentration.
Endosmosis and Exosmosis Difference
|
S.No |
Exosmosis |
Endosmosis |
| 1 | The movement of solvent outside the cell.
(Exo- outside) |
The movement of solvent inside the cell.
(Endo- inside) |
| 2 | Osmosis takes place outside a cell. | Osmosis takes place inside a cell. |
| Osmotic pressure is high. | Osmotic pressure is low. | |
| 3 | Exosmosis causes the cell to shrink. | Exosmosis causes the cell to swell. |
| 4 | Water travels from the cytoplasm of the cell, which contain comparatively less solute, into the surrounding solution, which contains relatively more solute. | Water travels from the surrounding solution, which has comparatively fewer solute, into the cell, whose cytoplasm contains relatively more solutes. |
| 5 | For example- Pickles’ salt addition aids in their preservation by plasmolysis of bacteria to kill off their cell. | For example- Plants use endosmosis to draw water from the surrounding soil into their root hair cell. |
Summary
There are two types of osmosis-endosmosis and exosmosis. What is the actual difference between both the processes is that during the process of exosmosis, water is removed from the cell, whereas during the process of endosmosis, the water transports itself within the cell. We have to discuss the concept of hypertonic, hypotonic, and isotonic solutions in this regard. A solution is hypertonic to the cell if it contains a solute concentration that is greater than that of the cell. It is hypotonic to the cell if the concentration of the solute is low. The two are termed isotonic in case there is the same concentration of the solute in the solvent and the cell sap.