Question

Why is the endoplasmic reticulum the most important organelle?

Answer 1

Because it extends a network from the nucleus. In simpler words as it arises from the outer nuclear membrane, and almost occupies the whole of the cytoplasm, it enables in transport of biochemicals. Moreover it also helps in Protein synthesis (RER) and synthesis of lipids and steroids (SER). Lastly it synthesises the nuclear membrane during cell division.
Hope this helps you.