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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 live in stagnant water, so do not search for them in flowing water, water from springs or tap water. Even in the free water of a lake or river there are few Protists and so in order to collect them you have to use special nets that concentrate them in a test tube. Instead, look for Protists close to the edge of ponds, puddles, fountains, vases with cut flowers, saucers, rainwater tanks, drains, etc.