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Life in Freshwater


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The Amoeba is the archetypal single-celled "animal". Belonging to the Protista it is not strictly an animal although the characteristics of the group are distinctly animal-like. The body is only one cell and microscopic although some species do reach proportions just visible to the naked eye. It has a large nucleus and a granular cytoplasm. The outline changes constantly as it moves and would be considered as asymmetrical. Single-celled organisms like the amoeba are very common, reaching very high levels of abundance in soil water and aquatic environments. By careful searching they can be removed from plants and stones in ponds, streams, rivers and lakes. A sample of estuarine mud under the microscope will reveal large lumbers of creeping amoebae. The parasitic forms of amoeba found on humans are, thankfully, rare in Europe .

ECOLOGY: The amoeba feeds on bacteria which it consumes by engulfing. This it does by surrounding it with false-feet or pseudopodia . These are extensions of the body which slowly project from the body surface. The internal cell cytoplasm streams forward spreading out somewhat like an "armoured tank track", being withdrawn at the back. In this way it moves forward and extends parts of the body to cover the food. Once inside the cell it forms a small vacuole. Enzymes are secreted into this vacuole to digest it. Amoebae are an important form of food for larger animals that consume micro-organisms. Amoebae reproduce by binary fission, which is when the cell divides into two. At times of drought they will produce a cyst within which they can tolerate dry conditions and high temperatures.

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