What is the primary function of the plasma membrane?

• A. To store genetic information
• B. To control substance movement in and out of the cell
• C. To generate cellular energy
• D. To facilitate protein synthesis

Answer: (B)

The primary function of the plasma membrane is to control the movement of substances in and out of the cell. This semi-permeable barrier is crucial for maintaining the internal environment of the cell, allowing it to regulate what enters and exits, thereby preserving homeostasis.

The plasma membrane is composed of a phospholipid bilayer with embedded proteins that assist in various transport processes. Some proteins act as channels or carriers to facilitate the passage of ions and molecules that cannot freely diffuse through the lipid bilayer. Additionally, the plasma membrane plays a role in signaling by allowing cells to communicate with their environment and respond to changes.

In contrast to other functions mentioned in the choices, the plasma membrane does not store genetic information, generate energy, or facilitate protein synthesis. These processes are instead conducted by the nucleus, mitochondria, and ribosomes respectively. Thus, the correct understanding of the plasma membrane highlights its essential role in substance regulation and the maintenance of cellular integrity.