What is the primary function of the plasma membrane?

• A. Separate the inside of the cell from the outside
• B. Store chromatin
• C. Produce energy
• D. Synthesize proteins

Answer: (A)

The plasma membrane's primary function is to separate the cell's interior from the external environment, forming a boundary that maintains cell integrity and controls what enters and leaves. The lipid bilayer provides a flexible, semi-permeable barrier, while membrane proteins act as channels, carriers, and receptors to regulate transport and communication with the surroundings. Chromatin is stored in the nucleus, not at the membrane, so chromatin storage isn’t the membrane’s job. Energy production happens mainly in mitochondria (and by cytoplasmic processes), not at the membrane. Protein synthesis occurs on ribosomes, not by the membrane itself.