In biology, a hypotonic cell environment is one with a lower concentration of solutes than the cytoplasm. In a hypotonic environment, osmosis causes water to flow into the cell. Plants thrive in hypotonic environments. Their cells have rigid cell walls that prevent bursting. In fact, the pressure of the cytoplasm against the cell wall keeps the plant from wilting and losing its shape.
On the other hand, cells without cell walls will swell and, if the environment is sufficiently hypotonic, burst and die. Some protists (such as Paramecium) counteract this with the use of contractile vacuoles that pump water out of the cell.
The opposite of hypotonic is hypertonic; the intermediate state is called isotonic.
