Final answer:
The plasma membrane is a phospholipid bilayer with proteins that acts as a selective barrier, controlling the passage of substances in and out of the cell.
Step-by-step explanation:
The plasma membrane separates the internal contents of a cell from the extracellular environment. It is a phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, forming a selective barrier. This membrane controls the passage of organic molecules, ions, water, oxygen, and wastes into and out of the cell, thus maintaining the proper conditions for cellular function. The plasma membrane separates the internal contents of a cell from the extracellular environment. It is a phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, forming a selective barrier.