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A contractile vacuole is a sub-cellular structure (organelle) involved in osmoregulation. It pumps excess water out of a cell and is found prominently in freshwater protists.They are found in both plant and animal cells. It pumps the water out from the cytoplasm.
In Paramecium, a common freshwater protist, the vacuole is surrounded by several canals, which absorb water by osmosis from the cytoplasm. After the canals fill with water, the water is pumped into the vacuole. When the vacuole is full, it expels the water through a pore in the cytoplasm which can be opened and closed. Other protists, such as Amoeba, have contractile vacuoles that move to the surface of the cell when full and undergo exocytosis.In amoeba contractile vacuoles collect excretory waste, such as ammonia, from the intracellular fluid by both diffusion and active transport.
The contractile vacuole stores extra water. If the cell has a need for water, the contractile vacuole can release more water into the cell. But if water is in excess, the contractile vacuole will remove it to maintain homeostasis. If you put fresh water protists in marine environment, its contractile vacuole will disappear. In protists, it is considered as an organelle for osmoregulation and excretion. But this only happens when the paramecium is grown in a culture.
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Wikisource has the text of the 1911 Encyclopædia Britannica article Contractile vacuole. |
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