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The contractile vacuole allows free-living protists to expel extra water. <b>The contractile vacuole allows free-living protists to expel extra water <br /></b>.
A contractile vacuole is an organelle in single-celled organisms that helps the cell remove wastes and excess water. It is found primarily in freshwater protists and algae. They are necessary because, in fresh water, the concentration of solutes inside a cell is greater than that outside the cell, so the cell constantly absorbs water through osmosis. In Paramecia , a typical freshwater protist, the vacuole is encompassed by a few waterways, which ingest water by osmosis from the cytoplasm.