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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>.
Protists are common, primitive organisms that live in pond water. Algae are plant-like protists, while protozoans are animal-like and are similar to very simple animals. Because they are photosynthetic, most algae are green; however, a few types are yellowish-brown.