Flexi Says: Organisms that live in a hypotonic environment such as freshwater, need a way to prevent their cells from taking in too much water by osmosis. A contractile vacuole is a type of vacuole that removes excess water from a cell. Freshwater protists have a contractile vacuole. The vacuole is surrounded by several canals, which absorb water by osmosis from the cytoplasm. After the canals fill with water, the water is pumped into the vacuole. When the vacuole is full, it pushes the water out of the cell through a pore. A contractile vacuole is of no use when paramecium is placed in a hypertonic or high salt concentration solution. This is because when salt concentration inside the paramecium is less than the outside environment, then they do not require contractile vacuole for the expulsion of the excess water.
