What is the primary role of the plasma membrane?

The primary role of the plasma membrane is to protect the cell's contents and regulate the movement of substances in and out of the cell. This semi-permeable membrane serves as a barrier that maintains the integrity of the cell by controlling which molecules can enter and exit, thus ensuring that essential nutrients can enter while waste products and harmful substances are kept out. Additionally, it plays a crucial role in cell signaling and communication with the external environment.

The other options highlight functions of different cellular components rather than the plasma membrane. For instance, storing genetic information is primarily the role of the nucleus; synthesizing proteins is associated with ribosomes and the endoplasmic reticulum; and producing energy is mainly the responsibility of mitochondria. Each of these processes occurs inside or involving different cell structures, underscoring the unique and specific functions of the plasma membrane in cellular biology.