Structure of the Cell Membrane

• The cell membrane is composed of a double layer of phospholipid molecules.
• It contains proteins that are either embedded within the membrane or attached to the surface.
• Cholesterol molecules are interspersed within the phospholipid bilayer, providing stability to the membrane.
• Carbohydrates are present on the outer surface of the membrane, serving as recognition sites for cell-cell communication.

Functions of the Cell Membrane

• Regulates the passage of substances in and out of the cell.
• Provides structural support and shape to the cell.
• Facilitates cell recognition and communication with other cells.
• Participates in cell signaling and signal transduction processes.

Transport Across the Cell Membrane

• Passive transport: Includes diffusion and osmosis, and does not require energy input from the cell.
• Active transport: Involves the movement of substances against their concentration gradient, requiring energy in the form of ATP.
• Facilitated diffusion: Utilizes specific carrier proteins to transport substances across the membrane.
• Endocytosis and exocytosis: Processes by which large molecules are transported into or out of the cell via vesicles.

Role of the Cell Membrane in Homeostasis

• The cell membrane helps maintain the internal balance of the cell by regulating the passage of ions, nutrients, and waste products.
• It prevents the entry of harmful substances into the cell and allows essential molecules to enter.
• Through selective permeability, the cell membrane ensures that the cell's internal environment remains stable and functional.