Which part of the cell acts as a barrier between the cell and its environment?

The cell membrane, also known as the plasma membrane, serves as the primary barrier between the cell and its external environment. It is composed of a phospholipid bilayer that provides structural integrity to the cell while regulating the movement of substances into and out of the cell. This selective permeability ensures that essential nutrients can enter the cell, waste products can be expelled, and the internal environment can be maintained within certain limits.

The cell membrane is also vital for communication with other cells and the environment. It contains proteins that act as receptors for signaling molecules, allowing the cell to respond to external stimuli. Additionally, the flexibility of the cell membrane allows for the cell to change shape, which is essential for various cellular processes including growth, division, and movement.

In contrast, the cell wall, found in plant cells and some bacterial cells, offers extra support and protection but is not present in all cell types. The cytoplasm is the gel-like substance inside the cell where various organelles reside, and it does not serve as a barrier. The nucleus houses the genetic material of the cell and is surrounded by its own membrane, but it is not responsible for the boundary between the cell and its environment. Thus, the cell membrane's key functions and structure make it the