Cell Membrane is the structure surrounding and protecting the cell and determines what enters and leaves the cell. Which option correctly identifies this structure?

• A. Cytoplasm
• B. Cell Membrane
• C. Nucleus
• D. Ribosome

Answer: (B)

The cell membrane is the boundary that surrounds the cell, protecting its interior while also controlling what passes into and out of the cell. It’s a phospholipid bilayer with embedded proteins and other molecules that create selective permeability, meaning only certain substances can cross easily while others are restricted. This boundary and transport control are exactly what the description is referring to.

Why the other structures don’t fit as the boundary: the cytoplasm is the internal, jelly-like substance inside the membrane; the nucleus houses genetic material inside the cell; ribosomes are the sites of protein synthesis. None of these form the enclosing boundary that regulates entry and exit, so they aren’t the structures described.