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2.8 Tonicity and Osmoregulation



⏱️  2 min read

written by

Tejas Bhartiya

tejas bhartiya

June 8, 2020

The movement of water inside and out of the cell is essential to it's survival. Water, just like all other substances, travels from a higher concentration of itself to a lower concentration of itself. This movement can have large impacts on the cell.

Depending on the amount of material outside of a cell compared to inside, the environment outside of a cell can be hypotonic, hypertonic or isotonic to the internal environment of a cell. 

A hypotonic solution is one that has LESS solute than the inside of the cell. In this case, water will move to where there is MORE solute (and therefore less water!). Water will move into the cell, causing the cell to expand. **think HYPO- HIPPO**🦛

A hypertonic solution is one that has MORE solute in it than there is inside of the cell. In this case, water will still move to where there is MORE solute. Water will, therefore, move out of the cell, causing the cell to shrink. **think: when you’re HYPER you run outside** 🏃‍♀️An isotonic solution is one that has EQUAL solute in it to that of the cell. In this case, water moves equally in and out of the cell, with no net movement. The cell does not change shape. 💧 Water will attempt to move from an area of high concentration to an area of low concentration until there are equal amounts of water on both sides of the membrane. This is called osmosis. Osmosis allows organisms to control their internal solute composition and water potential.

Below are examples of hypertonic, isotonic, and hypotonic solutions for both a blood cell and a plant cell. As you can see, plant cells are more able to exist in a hypotonic environment due to their cell wall. 

Animal Cell:


Image courtesy of Wikipedia

Plant Cell:


Image courtesy of Wikipedia

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