Osmosis (Meaning and Explanation)

We explain what osmosis is and the types that exist. Also, why it is important, what biological diffusion is and examples of osmosis.

What is osmosis?

Osmosis or osmosis is a physical phenomenon of matter exchange through a semipermeable membrane from a less dense medium to a higher density medium, without incurring energy expenditure. It is a passive phenomenon, but vital for the cellular metabolism of living beings.

The mechanics of osmosis pursue an equilibrium of concentrations between the two segments of a solution separated by the membrane, transmitting solvent from one side to the other to dilute the end with the highest concentration. This will generate a change in pressure, known as osmotic pressure. This is what happens with the cell membrane, whose interior can be at a higher, equal or lower concentration than the outside, allowing the entry and exit of water, that is, osmoregulation, without energy cost.

osmosis It was discovered in 1877 in studies on plant physiology by the German Wilhelm Pfeffer despite the fact that similar studies already existed on the subject and the term had been coined in 1854 (by the British Thomas Graham).

Types of osmosis

reverse osmosis — Reverse osmosis goes from the point of highest to lowest solute concentration.

There are two forms of osmosis: direct and reverse.

Direct osmosis. It is the one that occurs in the cells of living beings, in which water enters or leaves through the plasma membrane, allowing a balance with the environment, although in cases of hypertonic media (with enormous concentration of the solute) or hypotonic ( minimum concentration of the solute) can cause dehydration or explosion due to cell accumulation, respectively.
Reverse osmosis. It is an identical mechanism but in the opposite direction, which allows the flow of water or solvent from the point of highest concentration to the point of lowest solute concentration, which is ideal for purification or solute retention purposes. For this to occur, a pressure must be applied that overcomes the natural osmotic pressure (i.e., requires an energy cost).

Importance of osmosis

Osmosis is vital for cellular metabolism, since It is a form of transport of matter between the inside and outside of the cell that does not entail any energy expenditure, that is, it is produced passively, without consuming ATP. This principle is also fundamental to explain the origin of life, given that in the first forms of cellular life there would not yet be active metabolic mechanisms.

On the other hand, the principles of osmosis can be replicated in everyday situations and allow, for example, the filtering of water (reverse osmosis), among other practical procedures such as manufacturing catalysts or facilitating industrial refrigeration processes.

Biological diffusion

A process similar to osmosis is known as simple diffusion, from the point of view in which it involves the transit of particles from one medium (such as the cell interior) to another (such as the extracellular environment) through a semipermeable membrane, moving from the medium of higher concentration to the medium of lower concentration (that is, following the concentration gradient). This takes place passively, that is, without additional energy consumption.

According to this, biological diffusion is what takes place in cells, allowing the entry or exit of molecules through the plasma membrane according to the concentration gradient. This is how, for example, oxygen enters the blood into the red blood cells, where hemoglobin can capture them for transport. This single example denotes the vital importance of this mechanism for life.

Examples of osmosis

Some simple examples of osmosis are:

The purification of water To remove impurities from water, the principle of reverse osmosis can be applied, to separate the contents dissolved in it through a semipermeable membrane.
The hydration of an egg The shell of an egg operates as an osmotic membrane, allowing water to enter its interior (more concentrated), so a boiled egg can be soaked without breaking its shell.
Cellular osmosis Part of the cellular transport mechanisms that allow the exchange (entry or exit) of matter between the cytoplasm and the environment without consuming ATP in the process.