Hypertonic, Isotonic and Hypotonic

In a hypertonic solution, the concentration of solutes in the solution is higher and so it has a lower water potential. Therefore, when placed in a hypertonic solution, water leaves the cell by osmosis, until equilibrium is established.

If the cell loses too much water, the cell will shrivel and shrink. Eventually they die, as their metabolism is disrupted i.e. badly wilted plants never recover fully.

Conversely, cells in a hypotonic solution will absorb water by osmosis until equilibrium is reached, since the cell has the lower water potential, and water ‘flows downhill’.

This flow of water into a cell causes it to swell:

a. Animal cells placed in a hypotonic solution will swell and often burst because of osmosis.

b. Plant, fungal and bacterial cells do not burst because of their cell wall. The pressure that the cell exerts against the cell wall is its pressure potential. These cells are normally in this state, i.e. turgid.

In an isotonic solution, the concentration of solutes on both sides of the membrane is the same and so the net movement of water is zero. This is the normal position inside an animal’s body.