What is the definition of osmosis?
Osmosis is a process of vital importance to maintain the osmotic balance that allows cells to function, and in the water sector it is used as a desalination option.
Osmosis is a biological process that involves passive diffusion; it occurs when two solutions with a different concentration of solutes are separated by a semipermeable membrane (which only lets the solvent through). This process occurs spontaneously, without any input of energy.
Three terms are used to compare two aqueous solutions separated by a semipermeable membrane:
- Hypotonic solution: the solute concentration is lower than that of the adjacent solution.
- Hypertonic solution: the solute concentration is higher than that of the adjacent solution.
- Isotonic solution (balanced): when both solutions have the same concentration.
During the process of osmosis, the solvent will diffuse from the side with a lower solute concentration (more diluted), crossing the semipermeable membrane to the side with a higher solute concentration, until both sides have equal solute concentrations. This process takes place from hypotonic solutions towards hypertonic solutions.
he process of osmosis can occur inside organisms, or in outside media.
- For instance, inside organisms red blood cells could be in a hypertonic solution. To equalise the concentration with the outside solution, water moves out of red blood cells, causing them to shrink and potentially causing death. On the other hand, when the solution is hypotonic, water moves into red blood cells, causing them to swell, something that can burst and kill the cells (cell lysis).
- In outside media, for example, living beings such as plants exposed to saline environments (high concentration solutions) are subject to high osmotic pressure, so they require an osmoregulation system to tolerate salinity.
Osmotic pressure is the extra pressure which needs to be applied to a solution to stop the inward flow of solvent across a semipermeable membrane.