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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>.
Amoeba have special vacuoles that fill up with water, then moves outside of the cell and bursts. The concentration of water outside the amoeba is higher than inside the cell, â¦because the vacuole contains mineral salts. So the concentration of water inside the vacuole is low.