Is Osmosis Hypotonic?  Why Or Why Not & Facts You Should Know

 Osmosis refers to a type of molecular movement from concentrated to diluted areas through a barrier.

Osmosis itself is not hypotonic since it is the solvent molecule moving from the hypertonic to the hypotonic solution. Osmosis is a passive diffusion process where solvent molecules move from higher (hypertonic solution) to lower concentrations passing through a semi-permeable membrane.

What solution causes osmosis?

Osmosis causes the diffusion of solvent molecules from a hypertonic solution to a hypotonic solution across a semi-permeable barrier, which in most biological cases refers to the cell membrane.

 A hypertonic solution is found when the concentration of the solution is greater outside than inside the cell. In this case, the solvent molecules move out of the cell, thereby causing it to deflate.

Image showing how osmosis works Image: Wikipedia

On the other hand, hypotonic solutions are found in the scenario where the concentration inside the cell is greater than that outside. So the solvent molecules move into the cell thereby inflating it or ultimately bursting it.

In both cases, the main purpose is to create an isotonic solution where the concentrations on both sides of the cell membrane become the same.

Hypotonic, hypertonic and isotonic solution:

In biological terms, most cells are found in blood or other body fluids so hypertonic, hypotonic and isotonic are considered concerning them.

How different tonicity affects blood cells
Image: Wikipedia

Hypertonic solution:

When the solution has a concentration greater than that in the blood or fluid that the cell is in, then the cell cytoplasm I considered a hypertonic solution. In this case, osmosis is endosmosis, as the solvent goes into the cell leaving the medium i.e the blood.

Hypotonic solution:

When the solution has a concentration lower than that in the blood or fluid that the cell is in, then the cell cytoplasm I considered a hypotonic solution. In this case, the solvent molecules move into the blood by the process of exosmosis.

Isotonic solution:

When the solution has a concentration of molecules that is the same as that in the blood or fluid that the cell is in, then the cell cytoplasm I considered an isotonic solution. In this case, there is no movement of solvent molecules.

Does hypotonic solution cause osmosis?

A hypotonic solution means that the concentration of solutes in that solution is lower than across the membrane. This causes exosmosis for the solvent molecules.

The solvent molecule moves across the plasma membrane into the cell exterior to make the concentrations a bit similar. This is the major reason that such solutions are used for energy drinks as they get absorbed onto the body stream quickly. This allows it to rehydrate and energize at a quicker rate.

Does osmosis occur in a hypotonic solution?

Osmosis occurs in both hypotonic and hypertonic solutions, just that the direction of flow of solute molecules is reversed. In the case of a hypotonic solution, osmosis occurs from it rather than in it.

Osmotic flow in a hypotonic solution Image: Wikipedia

Since osmosis involves the movement of solvent molecules rather than the solute molecules, soo it is the opposite of normal diffusion. Since a hypotonic solution has a lower concentration of solute molecules, so it loses the solvent molecules to the solution with a higher concentration.

How does osmolarity affect osmosis?

Osmolarity, now called osmotic concentration is the measure of the concentration of a solution as in the amount of the solute in a specific amount of solvent.

As osmolarity is a measure of concentration, osmosis occurs from solutions of lower to higher osmolarity.

Since osmosis moves the solvent molecules from areas of lower to a higher concentration of the solvent, hence it goes from a less concentrated to a more concentrated solution.

What is hypotonic osmolarity?

Hypotonic osmolarity is actually lower than that of blood or the medium across the membrane.

This means that exosmosis occurs from high osmolarity hypotonic solution into the blood or the media across the membrane. Low osmolarity means that the solution has a higher concentration of solvent molecules as compared to solute molecules.

The osmolarity of the solution is comparatively lower than that of blood, which makes it hypotonic. So the solution in comparison is equally important for consideration of tonicity.

Is high osmolarity hypertonic?

High osmolarity does not actually mean that the solution is hypertonic. In order to the hypertonic, the solution must have an osmolarity greater than that of blood.

Osmotic flow in a hypertonic solution Image: Wikipedia

Only if the osmolarity of the mentioned solution is greater than that of blood or the fluid across the membrane will it be considered hypertonic. If the previous statement is true then the cell will experience endosmosis.

This means that solvent molecules will move into the cell to equate the concentration in the cell and blood. This allows rehydration of the cell.


The question “Is osmosis hypotonic?” is not correct. Osmosis can occur in both hypertonic and hypotonic solutions, but the direction is the opposite in both cases.

Trisha Dey

I am Trisha Dey, a postgraduate in Bioinformatics. I pursued my graduate degree in Biochemistry. I love reading .I also have a passion for learning new languages. Let’s connect through linked in:

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