What is Hypotonic Solution?
The term hypotonic is made from two Greek words, hypo means under and tonos means stretching. A hypotonic solution means a solution with lesser concentration of solutes as compared to another solution.
In biological terms, there is a lower concentration of solutes outside the cell than inside in hypotonic solutions. If there is a lower concentration of solute outside the cell water will rush inside the cell in order to balance between the both inside and outside solutions. In case of animal cells, this inward movement of solutes may cause the cell to burst. While, in case of a plant cell, turgor pressure saves the cells from bursting. Turgor pressure means cell vacuole drinks up extra water and pushes the cell membrane against cell wall, and because of its rigidity cell wall pushes it back.
Types of Solutions
A solution can be one of these three solutions when compared to another solution. It can be an isotonic solution, in which there is equal concentration of the solutes in the solution as compared to the other. It can be a hypotonic solution, which has low concentration of solutes in the solution in comparison to the other solution. Or it can be a hypertonic solution, in which a solution has more concentration of solutes as compared to other solution.
What is Tonicity?
Hypotonic solution, isotonic solution and hypertonic solution, all have the word tonic in common. Tonic refers to the tonicity of the solution. Tonicity is a measure of relative concentration of solutions which determine the extent as well as direction to which diffusion will occur. Or we can say tonicity is a measure of osmotic pressure gradient between two solutions which are separated by a membrane, more specifically a semipermeable membrane.
Tonicity is affected by those solutes which cannot pass the membrane and these solutes only exert effective osmotic gradient. Those solutes which can freely and easily cross the membrane will always be in an equal concentration inside and outside the cell and do not affect tonicity.