What is the primary function of the cell membrane?

The primary function of the cell membrane is to enclose the main body of the cell and regulate the passage of substances. This semi-permeable barrier separates the interior of the cell from its external environment, providing structural integrity while allowing selective transport of ions and molecules. The cell membrane consists of a phospholipid bilayer with embedded proteins that can function as channels, receptors, and enzymes, contributing to the regulation of what enters and exits the cell. This regulation is crucial for maintaining homeostasis, enabling the cell to carry out its metabolic activities, respond to external signals, and maintain its overall environment.

The other options refer to functions not primarily associated with the cell membrane. While energy production occurs in structures such as mitochondria, genetic material is stored in the nucleus, and cellular respiration is a complex process involving multiple cellular components and pathways.