Amoeba (magnified).—Russ Kinne/Photo Researchers

One-celled protozoan that can form temporary extensions of cytoplasm (pseudopodia) in order to move about. Some amoebas are found on the bottom of freshwater streams and ponds. Others live in the human digestive system; one type causes amebic dysentery in humans. Each amoeba contains a small mass of jellylike cytoplasm with vacuoles and a nucleus. Food is taken in and material is excreted at any point on the cell surface. Amoebas are used extensively in cell research for determining the relative functions and interactions of the nucleus and the cytoplasm.

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