What is the primary function of the cell membrane?

The primary function of the cell membrane is to protect the cell and regulate the movement of substances. The cell membrane, also known as the plasma membrane, serves as a barrier that separates the internal contents of the cell from the external environment. This selective permeability is crucial for maintaining homeostasis within the cell.

It allows certain molecules to enter or exit the cell while keeping harmful substances out, thus ensuring that essential nutrients and ions can be taken in and waste products can be expelled. Additionally, the membrane is involved in cell signaling and recognition, playing a role in communication between cells.

In contrast, other functions mentioned in the options are performed by different cellular structures. The synthesis of proteins and lipids predominantly occurs in the endoplasmic reticulum and ribosomes, while genetic information is stored in the nucleus. Energy generation primarily occurs in the mitochondria. Therefore, while all functions are vital for the cell's overall operation, the specific role of the cell membrane in protection and regulation of substance movement is fundamental to cellular life.