Osmosis. How does reverse osmosis work and what is it?

Osmosis occurs spontaneously as a result of the passage of a solvent (e.g. water) through a semipermeable membrane from a solution with a lower concentration of a solute to a solution with a higher concentration, equalizing the concentration of each of them. How does osmosis work? What is reverse osmosis phenomenon?

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1. What is osmosis?

Osmosis is the diffusion of a solvent through a semi-permeable membrane that separates two solutions of different concentration. The solvent passes from a solution with a lower concentration (hypotonic) to a solution with a higher concentration (hypertonic).

The purpose of the movement of molecules is to equalize the concentration between the two solutions, and at the same time to equalize the hydrostatic pressure exerted on the membrane with the osmotic pressure that arises due to the difference in chemical potentials between the solutions.

If a cell is placed in a hypertonic solution, water will flow from the cell to the outside, and the cell will lose its firmness. This phenomenon is observed in plant cells.

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If we put a plant cell in a solution with a higher concentration (eg NaCl), as a result of this action, water will leak from the cell, and at the same time the vacuole will shrink, and the protoplast will start to stick out from the cell wall. This phenomenon is called plasmolysis.

Plasmolysis is a reversible process because when this cell is placed in a hypotonic solution, the water will flow back into the cell and return to its original state. This phenomenon is called deplasmolysis. However, if the cell is stored in a hypertonic solution for a long time, the cell membrane may rupture and the cell rupture.

2. How does osmosis work in living organisms?

The cells of living organisms in contact with a hypotonic solution become larger. If a cell does not have a cell wall, it can even burst.

Similarly, these cells, when they end up in a hypertonic solution, contract and undergo plasmolysis to varying degrees. An example is gargling with a special salt solution - the solution deprives bacterial cells of water and causes them to die due to dehydration and denaturation.

In plants, due to osmotic phenomena, they transport water from the roots to the leaves. Thus, the osmosis phenomenon provides the plants with stiffness of stems and leaves (in cooperation with some tissues), and is also the basis for the operation of the stomatal apparatus.

In animals, osmosis is part of the homeostasis process.

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3. Reverse osmosis - what is it?

The osmosis phenomenon can be stopped or even reversed by applying a sufficiently high pressure to the hypertonic solution. We are talking then about reverse osmosis, which has been used, inter alia, to desalinate sea water.

Reverse osmosis has also been used in water filters for years. It is worth remembering, however, that although as a result of reverse osmosis we get rid of as much as 96% of impurities from water, it also loses valuable minerals, such as calcium and magnesium. If we are going to consume such purified water in large amounts, it is worth taking care of its mineralization.

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