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Difference between Hypertonic, Hypotonic, Isotonic Solutions

Memorizing the definition of hypertonic, hypotonic, and isotonic solutions is not necessary when you understand the root words that make up these descriptive words. The difference between the words hypertonic, hypotonic, and isotonic describe the tonicity. Tonicity is the difference in water concentration of two solutions separated by a semipermeable membrane. Knowing the tonicity of solutions will tell you which direction water will diffuse.

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 Comparison Chart


[easytable] Let us compare,Hypertonic,Hypotonic,Isotonic

Relative Concentration, Higher,Lower,Equal

Effect on cell in this environment,Shrink,Swell or Burst,No Net Effect

Root word,Hyper-,Hypo-,Iso-

Root meaning,Above,Below,Equal

Root word example,Hyperactive,Hypothermia,Isotope


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Break the Words into Parts

Breaking the words into parts will allow you to figure out the difference in concentration, and how cells will respond on the fly.  No more memorization is needed!

Hyper (tonic)

Hyper is a synonym for “above or excessive“.  Think of  hyperactive kids which means overly active kids. Hypertonic solutions will have a higher concentration of solute than than the solution its being compared to. See How Cells Respond below to see how cells respond to hypertonic environments.

Hypo (tonic)

The root word hypo means “below“. Think of people who are in cold temperatures that get hypothermia. The body temperature is below normal. See  How Cells Respond below to see how cells respond to hypotonic environments,

Iso (tonic)

The root word iso means “equal”.  If you remember hypertonic and hypotonic are higher and lower concentrations then isotonic must be the case where both solutions have equal concentration. See  How Cells Respond below to see how cells would respond.


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How Cells Respond

Many times when talking about tonicity examples of red blood cells in a solution are used. In cases like this, a cell in solution, the tonicity refers to the environment around the cell and NOT the concentration inside the cell.

Hypertonic environment

Hypertonic solutions will have a higher concentration of solute (glucose, salt, etc) than the cell. Mainly water will move across the cell membrane in order to even out the concentration of solutes in both the cell and the environment around the cell. The cell will shrink  as water leaves the cell to decrease the higher concentration of solute in the environment.

Hypotonic environment

Hypotonic environments will have a lower concentration of solute  than the cell. Water will move from the environment into the cell in order to balance the concentration of solute. When water diffuses into the cell it will swell. Sometimes the cell may lyse or burst due to the excess water uptake.

Isotonic environment

Isotonic environments have the same concentration of soules as the cell. Water will diffuse both in and out of the cell, but no net effect will be seen.

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