Do you notice any similarities between the words hypertonic, hypotonic, isotonic?
If you spotted that the last five letters of each word spells tonic, congratulations. Youve just learned that tonicity is the basis of classifying these solutions.
So whats all this tonicity about?
Tonicity refers to the ability of a solution to alter the internal water volume of a cell. For instance, cells can get skinny, fat, or stay the same depending on thier tonicity. But nobody says, hey look at that fat red blood cell under a microscope. (At least nobody Ive ever met does.)
Instead, science adds a prefix to tonic for classification purposes. These prefixes include hyper, which means excessive; hypo, which means deficient; and iso, which means the same. This is the basis for the names hypertonic, hypotonic, and isotonic.
We know from the prefix iso that isotonic solutions when exposed to a solution should keep their normal shape. The osmotic pressure outside the cells is the same as the osmotic pressure inside the cells.
Well use red blood cells as an example. Normal sized red blood cells are round and are concave. When these cells exist in an isotonic solution one in which the concentration of solutes is the same inside the cell as outside the cell water exits and enters the cell at the same rate. This is the normal balance of a red blood cell.
The prefix hypo means deficient. A hypotonic solution will have a lower concentration of solutes than the cell. The cell will also have a higher osmotic pressure the tendency for water to move into a cell by osmosis than the solution surrounding it. This will cause fluid to move into the cell.
When the solution outside of the red blood cells has a lower osmotic pressure than the cytoplasm of the red blood cells, the solution is hypotonic with respect to the cells. The cells take in water in an attempt to equalize the osmotic pressure, causing them to swell and potentially burst.
For example, a hypotonic solution like distilled water will have a high concentration of water with no solutes. If distilled water is used to hydrate red blood cells, the distilled water will move by osmosis into the cells, where theres a lower concentration of water. This is the cells attempt to equalize osmotic pressure.
The result: The red blood cells swell, then burst also known as lyse.
Hyper means too much. A hypertonic solution will have a higher concentration of solutes than the cell and will have a higher osmotic pressure outside the cell than inside the cell.
This will cause the water to be pulled from the cell, which results in the cells attempt to equalize osmotic pressure. The cell will crenate shrink.
I hope this information about hypertonic, hypotonic, isotonic solutions has been helpful.