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( Eukaryote)
Animals, plants, fungi, and protists are eukaryotes (IPA /ju?'kær??t/ or IPA /-o?t/), organisms whose cells are organized into complex structures enclosed within membranes. The defining membrane-bound structure which differentiates eukaryotic cells from prokaryotic cells is the nucleus. The presence of a nucleus gives these organisms their name, which comes from the Greek e?, meaning "good/true", and ??????, "nut". Many eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies. Eukaryotes often have unique flagella made of microtubules in a 9+2 arrangement. Eukaryotes appear to be monophyletic, and so make up one of the three domains of life. The two other domains, bacteria and archaea, are prokaryotes, and have none of the above features. But eukaryotes do share some aspects of their biochemistry with archaea, and so are grouped with archaea in the clade Neomura. Eukaryotic cells are typically much larger than prokaryotes. They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments, and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. Eukaryotic cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. Simple compartments, called vesicles or vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles.
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