What distinguishes smooth endoplasmic reticulum from rough endoplasmic reticulum?

The distinction between smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER) primarily lies in the presence of ribosomes on their surfaces. The rough endoplasmic reticulum is studded with ribosomes that give it a "rough" appearance and are vital for protein synthesis. In contrast, the smooth endoplasmic reticulum lacks these ribosomes, which is why it appears smooth.

The smooth endoplasmic reticulum plays a crucial role in the synthesis and transport of lipids. It is involved in lipid metabolism, including the production of phospholipids needed for cell membranes and the synthesis of steroid hormones. Additionally, the SER is responsible for detoxifying certain chemicals and storing calcium ions, which are important for various cellular functions.

Ribosomes and protein synthesis are characteristic features of the rough endoplasmic reticulum, while the smooth endoplasmic reticulum's primary functions revolve around lipid transport and metabolism. Thus, the ability to transport lipids is what distinguishes the smooth endoplasmic reticulum from the rough endoplasmic reticulum. This specificity in function highlights the distinct roles that each type of endoplasmic reticulum plays within a cell.