It is mainly responsible for the transportation of proteins and other carbohydrates to another organelle, which includes lysosomes, Golgi apparatus, plasma membrane, etc.
They play a vital role in the formation of the skeletal framework.
They provide the increased surface area for cellular reactions.
They help in the formation of nuclear membrane during cell division.
They play a vital role in the synthesis of proteins, lipids, glycogen and other steroids like cholesterol, progesterone, testosterone, etc.http://biology.tutorvista.com/animal-and-plant-cells/endoplasmic-reticulum.html
