Describe ER its functions its parts

Endoplasmic reticulum is a continuous membrane, which is present in both plant cells, animal cells and absent in prokaryotic cells. It is the membrane of network tubules and flattened sacs, which serves a variety of functions within the cell. The space, which is present in the endoplasmic reticulum, is called as the lumen.  
The major functions of Endoplasmic reticulum are:

1. It is mainly responsible for the transportation of proteins and other carbohydrates to another organelle, which includes lysosomes, Golgi apparatus, plasma membrane, etc.
2. They play a vital role in the formation of the skeletal framework.
3. They provide the increased surface area for cellular reactions.
4. They help in the formation of nuclear membrane during cell division.
5. They play a vital role in the synthesis of proteins, lipids, glycogen and other steroids like cholesterol, progesterone, testosterone, etc.