Final answer:
Rough ER is studded with ribosomes and involved in protein synthesis, whereas smooth ER is involved in lipid production; both are interconnected structures within the cell.
Step-by-step explanation:
The key differences between rough ER (RER) and smooth ER (SER) lie in their structure and functions. The RER is called 'rough' due to the presence of ribosomes on its membrane, giving it a bumpy appearance. It is primarily involved in the synthesis of secretory and membrane proteins. On the other hand, the SER lacks ribosomes and is involved in the production of lipids. Both types of ER are connected and form a continuous network within the cell but have distinct roles in cellular metabolism.