Here's why:
* Cell wall: This rigid structure is found in plant cells, bacteria, fungi, and some protists. It provides structural support and protection. Animal cells lack a cell wall.
* Plasma membrane: This thin, flexible layer is composed of a phospholipid bilayer and embedded proteins. It's present in all cells and plays a crucial role in:
* Regulation of what enters and leaves the cell: It acts as a selective barrier, allowing certain molecules to pass through while blocking others.
* Cell signaling: Receptors on the plasma membrane receive signals from the environment, triggering responses within the cell.
* Maintaining cell shape: Although not as rigid as a cell wall, the plasma membrane provides some structural integrity to the cell.
So, while cells without a wall don't have the rigid protection of a cell wall, the plasma membrane is essential for defining their boundaries, controlling their internal environment, and interacting with the outside world.
