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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 animals: Many unicellular organisms like Amoeba throw out their wastes by diffusion from their body surface. Protozoanâs have no organs for excretion. As they live in an aquatic habitat, their wastes are eliminated by diffusion through the plasma membrane.