In biology, the term describes a cell environment with a lower concentration of solute than the cytoplasm of the cell. Given a cell placed in a hypotonic environment, osmosis causes a net flow of water into the cell, with a chance of causing the cell to burst and not function.

Solutions and cell environments are also described, in terms of osmotic pressure, as being either hypotonic, hypertonic or isotonic.

Plants thrive in hypotonic environments. Their cells have rigid cell walls that prevents bursting, or lysis. The pressure of the cytoplasm against the cell wall keeps the plant from wilting and losing its shape. This pressure is called turgor pressure or osmotic pressure. On the other hand, cells without cell walls will swell and, if the environment is sufficiently hypotonic, burst (lyse) and die (referred to as cytolysis).

Some protists (such as Paramecium) counteract this with the use of contractile vacuoles that pump water rapidly out of the cell. Other organisms actually eject solutes from the cell in order to lower the concentration gradient of the solute in the cell and hopefully create an isotonic environment. Protists are a very small organism that only live in hypotonic environments.

See also

• Cytolysis
• Hypertonic
• Isotonic
• Intravenous therapy
• Hypotonia

References

• Thames Valley S. S. Ontario, Canada