What is the primary function of the cell membrane?

The primary function of the cell membrane is to control the movement of substances in and out of the cell. This selectively permeable barrier is vital for maintaining the internal environment of the cell, allowing it to regulate what enters and leaves, thus maintaining homeostasis. The cell membrane is composed of a phospholipid bilayer with embedded proteins that facilitate transport processes. These processes include passive transport mechanisms, such as diffusion and osmosis, as well as active transport, which requires energy to move substances against their concentration gradient.

This control over substance movement is crucial for many cellular functions, including nutrient uptake, waste removal, and communication with other cells. The other choices do not represent the primary role of the cell membrane; for example, energy production occurs in organelles like mitochondria, protein synthesis takes place in ribosomes, and genetic information storage is handled by DNA within the nucleus.