Which term refers to the outer boundary of a cell?

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

Answer: (A)

The outer boundary of a cell is the cell membrane, also called the plasma membrane. This phospholipid bilayer with embedded proteins forms a selective barrier that controls what enters and exits the cell, helping maintain the internal environment and protect the cell. It also defines the cell’s shape and participates in communication with other cells.

The nucleus sits inside the cell and houses genetic material, so it isn’t the boundary. The cytoplasm is the interior jelly-like material where organelles reside, not the boundary. Protoplasm is an older term referring to the living contents of the cell (including the cytoplasm and nucleus), not the boundary itself.