A cell membrane, also known as the plasma membrane, is a thin layer that surrounds and encloses the contents of a cell. It is composed of a lipid bilayer, which is made up of two layers of phospholipid molecules. These molecules have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail. The phospholipid molecules are arranged in such a way that the hydrophobic tails face each other, forming a barrier that separates the inside of the cell from the outside environment. This lipid bilayer is fluid and flexible, allowing the cell to maintain its shape and size. The cell membrane also contains proteins, which play various roles in the functioning of the cell. Some proteins act as channels or pumps, allowing certain molecules to enter or exit the cell. Other proteins act as receptors, allowing the cell to sense and respond to signals from its environment. The cell membrane is important for maintaining the integrity of the cell, as well as for controlling the exchange of substances between the cell and its environment. It also plays a crucial role in the communication and signaling between cells. In summary, the cell membrane is a thin layer that surrounds and encloses the contents of a cell, composed of a lipid bi-layer and proteins. It plays a crucial role in the functioning and communication of the cell.