The cell is the basic functional unit
   of life.
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   All  cells  are  bound  by  a  membrane  that  encloses  a  semi-fluid
   cytoplasm.
<P>
   Eukaryotic  cells  contain  membrane-enclosed  organelles, including a
   DNA-containing nucleus.
<P>
   Prokaryotic  cells  lack  organelles;  their DNA is not contained in a
   nucleus.