Osmosis Facts for Kids

Updated April 17, 2017

Osmosis is a scientific concept typically taught to children during elementary school. In osmosis, a solvent passes through a membrane from one region to another, which contains a solute. Osmosis takes place on the molecular level, and is typically used to describe how material passes from the outside a cell through the cell membrane inside the cell.


Osmosis is a type of diffusion, which is a process in which molecules spread from areas of higher concentration to areas of lower concentration. When all areas are at the same level of concentration, this is called equilibrium. Osmosis occurs when a solvent is diffused through a semipermeable membrane, transferring from an area of lower concentration to an area of higher concentration, called a solute. The solvent is able to permeate the membrane from the side of the membrane where the solution is strongest, but not the other way around, until equilibrium is achieved when the solution on both sides of the solution is the same.

Solvents and Solutes

Solutes are things such as proteins and ions that dissolve in a solvent, such as water. When this happens, the concentration level of the solute increases in these areas, causing the solvent to diffuse to areas where solute concentration is higher. This will continue until equilibrium is achieved and the concentration level is the same on both sides of the membrane. At this point, the solvent and the solute essentially become one and the same as the solute is equally distributed throughout the solvent.


An excellent example of osmosis occurring in the cells of the body can be seen in red blood cells. Red blood cells contain a high concentration of solutes such as salt and protein. When these cells are placed in a solvent solution of water, the water will rush into the area where solute concentration is higher. This influx of water, the solvent, will cause the cell to swell until it eventually bursts.

Reverse Osmosis

Osmosis can also work in reverse. In the process of reverse osmosis, a solvent can be moved through a membrane from an area of high solute concentration into an area of low solute concentration by applying pressure that is greater than that of the pressure that occurs in typical osmosis. This process has practical uses, as it can push a solution through a filter that traps the solute on one side of the filter while all that makes it through the other side is pure solvent. The reverse osmosis process is commonly used to purify water.

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