What is the definition of isotonic in biology

In biology isotonicity means two solutions are isotonic having the same solute concentration and same osmotic pressure compared to others. If the solution is isotonic with respect to the animal cells, there will be the same concentration of solute on both sides, creating water balance.

If the solution is in isotonic state with respect to the plant cells, the latter uses its turgor.

This term used to describe chemistry, and solution, and muscles in human biology.

also check: Pseudocoelomate definition in biology

What is isotonic in biology

The concept of isotonic can be used in different fields. In the field of chemistry, those solutions that have the same osmotic pressure when they are at the same temperature classifies as iso.

In hematology, solutions that have the same salt concentration as red blood cells are said to be an isotonic solution has. Therefore, they have the same osmotic pressure as blood and do not cause red blood cells to deform.


Applying this term to muscle contraction, a contraction is said to be isotonic when the muscle tension remains constant.

It should be remembered that a solution is a mixture that obtains when a solid dissolves in a liquid. The osmotic pressure, meanwhile, is the pressure exerted by the solvent particles on the semi-permeable membrane that establishes a separation with the more concentrated element. The temperature also is the physical quantity indicating the degree of heat of the environment or body.

Returning to the idea of ​​isotonic, two or more solutions are iso when, at the same level of heat, the solvent particles of each exert the same pressure on the semipermeable membranes.

Here’s the examples of isotonic. Let’s look in detail.

Examples of isotonic solutions:

Following are the concepts that describe what does isotonic solution mean.

Relieving Dehydration

A mixture of water and sodium chloride(NaCl) makes a saline solution. Saline solutions are often given to hospital patients undergo serious dehydration, or who cannot attain enough fluid intake via traditional consumption. An iso solution is given to the patient that undergoes severe hydration.

Isotonic saline solutions have the same concentration of NaCl as cellular fluids in the human body than hypertonic and hypotonic saline solutions.

Since they have the same concentration of NaCl as the iso saline solution, cells do not swell with extreme water, nor shrink by losing more water.

Iso saline solutions lessen the risk of fatal health problems, like heart failure.

Alcohol Proof

Beer has less alcohol content by volume, or lower proof, than whiskey. In scientific terms, whisky has a greater concentration of ethanol, which makes it more effective than beer. In simple words, beer is hypotonic to whiskey, and whisky, conversely, is hypertonic to beer.

Like beer, there are various low_alcohol varieties of wine. It has an iso solution if low-alcoholic wine having the same ethanol concentration as, beer, or has the same proof as beer.

Now, let’s compare it with other related head terms.

Isotonic vs hypertonic:

In an Iso-environment, has the same solute concentration while a hypertonic has a higher solute concentration. If the solution is hypertonic with respect to the animal cell the water will move towards the outside of the cell which shrivels and can die from dehydration.


Hypotonic is a solution with lower solute concentration. If the solution is hypotonic with respect to the animal cell the water will mover towards the inside of the cell which it swells and can burst. If the solution is hypotonic with respect to the plant cell, the cell is turgid.

To survive in a hypertonic or hypotonic environment, the cell must regulate its water balance.

Isotonic Exercises

An isotonic contraction implies that the muscle fibers register a change in length. If the muscle shortens, it is a concentric isotonic contraction; if the muscle lengthens, the contraction is isotonic and eccentric.

Push-ups are the same exercise, that gives isotonic muscles. Push-ups involve raising the body and lowering it in a plank position, so that is why push-ups are isotonic. On the other hand, Bicep Curls involve raising the arm and lowering it, to build muscle so, they are also iso activity.

However, only those activities are, which have the same tone.


The cell in an isotonic suspension is in equipoise with its neighboring, determining the solute absorptions within and outward are the corresponding. In this condition, there is no attention grade and hence, no substantial osmotic change outside and inside. Water do unobstructed migrate out and in the respective cell, so the water movement rate is identical inside as well outside.

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