The Endoplasmic reticulum (ER) is
   a membranous system continuous with the nuclear envelope.
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   Rough  ER  is  studded  on its outer surface with ribosomes to produce
   proteins.
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   Smooth ER lacks ribosomes and is involved in lipid synthesis.
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   Transport  vesicles  bud  off  and  carry  ER  products  to  the Golgi
   apparatus and other destinations.