Osmosis – Concept, types, importance and examples

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

Osmosis was discovered in 1877 by the German Wilhelm Pfeffer.

What is osmosis?

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

The mechanics of osmosis pursues 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 higher concentration end. This will generate a pressure change, known as osmotic pressure. This is what happens with the cell membrane, whose interior may be at a higher, equal or lower concentration than the exterior, allowing the entry and exit of water, that is, osmoregulation, without cost of energy.

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

Types of osmosis

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

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 an equilibrium with the environment, although in cases of hypertonic (high concentration of solute) or hypotonic ( of minimum solute concentration) can cause dehydration or explosion by accumulation of the cell, respectively.
  • Inverse 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 lowest concentration of solute, which is ideal for purification or retention of solute. For this to occur, a pressure must be applied that overcomes the natural osmotic pressure (ie, requires an energy cost).

Importance of osmosis

Osmosis is vital for cellular metabolism, since it is a form of matter transport 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, since in the first forms of cellular life there were still no 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 manufacture of catalysts or facilitate industrial cooling processes.

Biological diffusion

Biological diffusion - osmosis
In biological diffusion, molecules enter and leave through the plasma membrane.

A process similar to osmosis is known as simple diffusion, from the point of view in which it implies the transit of particles from one medium (such as the cell interior) to another (such as the extracellular environment) through a semi-permeable membrane, moving from the medium with the highest concentration to the one with the lowest concentration (that is, following the concentration gradient). This takes place passively, that is, without consumption of added energy.

Accordingly, biological diffusion is that which takes place in cells, allowing the entry or exit of molecules through the plasma membrane, according to the concentration gradient. Thus, 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:

  • Water purification. To remove its impurities from the water, the principle of reverse osmosis can be applied, to separate the dissolved contents in it by means of a semi-permeable 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 that a cooked egg can be soaked without breaking its shell.
  • Cell 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.