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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>.
(However, Euglena, which can be induced to lose their chloroplast, illustrate why unicellular algae are included with protozoa.). A photomicrograph of the protozoa Euglena. As is appropriate for heterotrophic organisms that capture food, most protozoa are motile (able to move).