Hypotonic vs Hypertonic
The diffusion of water molecules from a dilute solution to a concentrated solution through a semi-permeable membrane is called ‘osmosis’. Semi-permeable membrane only allows solvent particle to move across it and does not allow solute particles to move through the membrane. The solvent concentration gradient across the two solutions is the driving force for this process. Here, the less concentrated solution is known as the hypotonic solution while the more concentrated solution is known as the hypertonic solution. The net movement of solvent from hypotonic solvent to hypertonic solvent takes place due to the unequal osmotic pressure. The pressure required to maintain equilibrium with no net movement of solvent across the semi-permeable membrane is defined as the ‘osmotic pressure’. Tonicity is a measure of the osmotic pressure gradient, and it is used to describe when a cell is immersed in an external solution, which can be either hypotonic or hypertonic or isotonic.
Hypotonic solutions have less solute concentration than that of the inside cell. Hence the osmotic pressure of this solution is very low compared to other solutions. When a cell with a cytoplasm is immersed in a hypotonic solution, water molecules move inside the cell from the solution due to the osmotic potential. The continuous diffusion of water molecules into the cell would cause the cell swelling. This may result in cytolysis of the cell (rupture). In plant cells, the cells are not always ruptured due to their thick cell wall.
Hypertonic solutions have high concentrations of solutes than that of the inside cell. When a cell is immersed in a hypertonic solution, the water molecules inside the cell will move outside the solution, and the cell becomes distorted and wrinkled. This effect is called ‘crenation’ of the cell. In the plant cells, the flexible plasma membrane pulls away from the rigid cell wall, but remains joined to the cell wall at certain points due to the effect of crenation and finally results in the condition called ‘plasmolysis’.
What is the difference between Hypotonic and Hypertonic Solutions?
• The solution (water) concentration is high in hypotonic solutions while the solution concentration is low in hypertonic solutions.
• Solute concentration of hypertonic solution is high while that of hypotonic solution is low.
• Water molecules move into the cell when the cell is bathed in a hypotonic solution. In contrast, water molecules leave the cell (water inside the cell itself) when it is bathed in a hypertonic solution.
• When a cell with a cytoplasm is immersed in a hypotonic solution, endosmosis takes place. On the other hand, a cell immersed in a hypertonic solution, exosmosis takes place.
• Hypertonic solution causes the cell to shrink while hypotonic solution causes the cell to swell.
• Cytolysis may occur in cells due to hypotonic solutions whereas plasmolysis may occur in plant cells due to hypertonic solutions.
• For dehydration, hypotonic solutions can be used while hypertonic solutions can be used for hemorrhage.