Here's why:
* Rough ER: This portion of the ER has ribosomes attached to it, which are responsible for protein synthesis. The rough ER then packages and transports these proteins to other parts of the cell or outside the cell.
* Smooth ER: This portion of the ER is involved in the synthesis of lipids, steroid hormones, and detoxification. It also helps in transporting these molecules within the cell.
Therefore, the ER acts as a network of interconnected membranes that serve as a "highway" for the movement of molecules within the cell.
