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Nucleus - Nucleus (plural:nuclei.,which (DNA)

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Nucleus The most basic division of organisms separates the living world into two groups on the basis of those  possessing and those lacking a defined  nucleus  (plural:  nuclei ). The nucleus is an organelle, which  contains the major portion of the genetic material (DNA) of the cell and is surrounded by a  nuclear  membrane . The genetic material of Prokaryotes is not contained within a membrane-bounded  nucleus. Eukaryotes all have nuclei.  Cellularity The form (morphology) of an organism can be  unicellular  (one-celled) or  multicellular  (many- celled). Some unicellular organisms form filaments (strings of cells), others form sheets of cells held  together by pectins, and still others form colonies that give a superficial resemblance to  multicellularity. Unicellular organisms do not form  tissues  (similar cells organized into a functional  unit) nor  organs  (groups of tissues organized for a particular function). Some organisms alternate a 
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