Final answer:
The structure described is known as the cell membrane or plasma membrane, made of a phospholipid bilayer with embedded proteins, and it regulates cellular exchange.
Step-by-step explanation:
The structure being described is the cell membrane, also known as the plasma membrane. It is composed of a phospholipid bilayer with embedded proteins. The cell membrane separates the contents of the cell from its outside environment and regulates what enters and exits the cell. This membrane is indeed composed of a phospholipid bilayer with various membrane proteins embedded within it. These proteins and the lipid bilayer work together to regulate what enters and exits the cell, creating a selectively permeable barrier that maintains the cell's internal environment. Therefore, the correct answer to the question is B. cell membrane.