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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>.
EXCRETION IN AMOEBA. Amoeba is a unicellular organism found in fresh water. In amoeba carbon dioxide and ammonia are the main waster materials. These waste materials are excreted out by the process of diffusion through general body surface. In amoeba, contractile vacuoles also play some role in the removal of waste materials. The waste materials present in the cytoplasm of amoeba enters the contractile vacuole.