What serves as the boundary surrounding the cell?

The cell membrane is the structure that serves as the boundary surrounding the cell. It is a vital component of the cell, maintaining its integrity by enclosing its contents and providing a barrier between the internal environment of the cell and the external surroundings. The cell membrane is composed of a phospholipid bilayer with embedded proteins, which also play essential roles in transport, communication, and signaling between the cell and its environment.

The cytoplasm refers to the jelly-like substance inside the cell, where cellular components are suspended and where many metabolic reactions occur. The nucleus is the organelle that houses the cell’s genetic material and controls cellular activities, but it does not define the outer boundary of the cell. Tissue, on the other hand, is a group of cells working together to perform a specific function but is not a boundary surrounding individual cells. Therefore, the cell membrane is specifically responsible for separating the cell from its external environment, making it the correct answer.