Plasma Membrane
The plasma membrane, also known as the cell membrane, is a crucial structure that surrounds the cell and separates its internal environment from the external environment. It is a selectively permeable barrier that controls the movement of substances in and out of the cell.

Structure of Plasma Membrane
- The plasma membrane is mainly composed of a phospholipid bilayer, which consists of two layers of phospholipid molecules.
- Embedded within the phospholipid bilayer are proteins that play essential roles in cell communication, transport of molecules, and cell recognition.
- Cholesterol molecules are also present in the membrane, providing stability and maintaining its fluidity.

Functions of Plasma Membrane
- Selective Permeability: The plasma membrane regulates the passage of molecules in and out of the cell, allowing only specific substances to enter or exit.
- Cell Communication: Proteins on the membrane facilitate communication between cells and their environment.
- Transport: The membrane proteins help in the transport of ions and molecules across the membrane through various processes such as active transport and facilitated diffusion.
- Cell Recognition: The proteins on the membrane help the cell recognize and interact with other cells.
- Maintenance of Cell Shape: The plasma membrane plays a role in maintaining the shape and structure of the cell.

Importance of Plasma Membrane
The plasma membrane is essential for the survival and proper functioning of the cell. It protects the cell's internal environment, allows for communication with the external environment, and regulates the transport of molecules necessary for cellular processes. Without a functional plasma membrane, the cell would not be able to maintain homeostasis and carry out its various functions.