Question

Explain briefly the difference between the isotonic and isoismotic solutions.

Answer 1

In relation to cell sap, solutions can be three types- Hypertonic, hypotonic and isotonic solution. On the other hand, on the basis of measure of osmotic pressure of a solution, it can be three types- hyperosmotic, hypoosmotic and isosmotic solution. Tonicity is a measure of the osmotic pressure gradient between two solutions separated by a semipermeable mebrane, while osmolarity is a measure of the osmotic pressure of a given solution. An isotonic solution is defined as the solution with concentration equal to that of cell sap. If a cell is placed in isotonic solution there will be no net diffusion of water. As a result there is no change in the volume and weight of the cell.   Solutions having the same osmotic pressure but not necessarily the same concentration are said to be isosmotic solution.

Points	Isotonic solution	Isosmotic solution
Definition	A solution having the same concentration as that of cell sap or a body fluids.	Solutions having the same osmotic pressure, but not necessarily the same concentration.
Solutes	Contain only non penetrating solutes that cannot pass through a membrane.	Contain both penetrating and non penetrating solutes.
Relationship with osmotic pressure	Possess different osmotic pressures from the cells they surround.	Have the same osmotic pressure as the cells they surround.
Water absorption	There will be no net diffusion of water, i.e these solutions do not cause the cells to absorb water from the external medium or to lose water from the cells. Consequently, there is no change in the volume and weight of the cell.	As the solutions do not have the same solute concentration, these solutions cause cells to absorb water from surrounding or to lose water from the cells.