What is the Difference Between Isotonic and Isosmotic?

Isotonic and isosmotic solutions are often encountered in chemistry labs, and while they may seem similar, they have distinct differences:

• Isotonic: This term refers to a solution having the same solute concentration as in a cell or a body fluid. Isotonic solutions contain only non-penetrating solutes, meaning that the solutes cannot easily pass through the cell membrane. These solutions are biologically compatible and do not alter the solvent concentration in a second solution.
• Isosmotic: This term refers to the situation of two solutions having the same osmotic pressure. Isosmotic solutions can cause cells to either absorb water from the surrounding environment or lose water to the environment. These solutions are chemically and/or physically similar to each other.

It is possible for a solution to be isoosmotic but not isotonic. An example of this is a sucrose solution, which would be isoosmotic to a mammalian cell because mammals do not have transporters for sucrose, and sucrose cannot easily pass through the cell membrane. However, this solution would not be isotonic because it does not have the same solute concentration as a mammalian cell.

Comparative Table: Isotonic vs Isosmotic

Here is a table comparing the differences between isotonic and isosmotic solutions:

In summary, isotonic solutions have the same solute concentration as cells or body fluids, while isosmotic solutions have the same osmotic pressure as another solution, such as blood. Isotonic solutions do not cause cells to absorb or lose water, whereas isosmotic solutions can cause such changes in water movement. Isotonic solutions contain only non-penetrating solutes, whereas isosmotic solutions can contain both penetrating and non-penetrating solutes.