What is the primary role of the endoplasmic reticulum in a cell?

The primary role of the endoplasmic reticulum (ER) in a cell is indeed protein and lipid synthesis. The ER is a highly folded membrane system that comes in two forms: rough ER, which has ribosomes attached to its surface and is primarily involved in the synthesis of proteins that are either secreted from the cell or inserted into cell membranes; and smooth ER, which lacks ribosomes and is responsible for the synthesis of lipids, metabolism of carbohydrates, and detoxification of certain chemicals.

The rough ER is particularly crucial for synthesizing proteins that need to be processed and modified before they can fulfill their roles, such as enzymes and hormones. The smooth ER plays an equally important role in producing lipids that are essential for the formation of cellular membranes and for storing calcium ions, which are important for various cellular functions.

In this context, the other options do not describe the primary functions of the endoplasmic reticulum. DNA replication and repair are tasks handled primarily by other cellular components, such as the nucleus and associated repair enzymes. Energy production is mainly carried out by mitochondria, where ATP is generated through cellular respiration. Cell division, involving processes like mitosis, predominantly occurs through the activities of a different set of cellular structures. Thus,