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
Because epithelial tissue is capable of regeneration.
The skin consists of two tissues: the outermost, the epidermis, resting on a vascularized connective tissue, the dermis. In the epidermis, which includes several layers of cells, the outer layer is formed of dead cells that are desquamating and are constantly being replaced by proliferating basal cell cells. So, under normal physiological conditions, the epidermis, like all the epithelia, is in constant renewal. On the other hand, when accidentally, the upper parts of the epidermis are damaged as a result, for example, of a burn or a slight abrasion, the destroyed portion is regenerated thanks to an accelerated proliferation of basal epidermal cells.
The rock's age is being determined, and is determined hope I helped!