What is Endoplasmic Reticulum (ER) ?

 The Endoplasmic Reticulum consists of interconnected membranous cisternae ,  tubules and isolated vesicles . It present in almost all eukaryotic cells but it does not present in prokaryotic cells . The endoplasmic reticulum helps in the exchange of materials between the cytoplasm and the nucleus . Their are the two types of endoplasmic reticulum :- 

1) Smooth Endoplasmic Reticulum (SER)

2) Rough Endoplasmic Reticulum (RER)

-> Smooth Endoplasmic Reticulum (SER):-  It consist tubules and vesicles . Smooth ER is free of ribosomes . It is present near to the cell membrane . SER takes part in the synthesis of lipids, glycogen and steroids . 

-> Rough Endoplasmic Reticulum (RER) :- It mainly consist of cisternae . In RER , it bears ribosomes on its cytoplasmic surface . It is present deep in the cytoplasm . RER takes part in the synthesis of proteins. 

Common Functions of Endoplasmic Reticulum :-

1) The Endoplasmic reticulum helps to transport the material from one part of cell to another part of cell . 

2) The Endoplasmic Reticulum offers extensive surface for synthesis of a variety of materials. 

3) It provide the space for temporary storage of synthetic products such as glycogen . 

Reference book- Pradeep's Biology Text Book .