The plasma membrane functions as a selective barrier and communication interface, regulating what enters and leaves the cell. Its foundation is a lipid bilayer, primarily composed of phospholipids such as phosphatidylcholine, arranged with hydrophilic heads facing outward toward the aqueous environment and hydrophobic tails inward, creating a flexible and semi-permeable barrier. Cholesterol molecules interspersed within the bilayer maintain membrane fluidity and stability under varying temperatures. Membrane proteins, accounting for roughly half of its mass, include integral proteins that span the bilayer, serving as channels, transporters, or receptors, and peripheral proteins attached to surfaces, facilitating signaling, cytoskeletal interactions, and cell adhesion. Carbohydrates linked to proteins (glycoproteins) or lipids (glycolipids) on the extracellular side play critical roles in cell recognition, signaling, and immune responses. This intricate, dynamic organization enables the plasma membrane to maintain homeostasis, mediate intercellular communication, and adapt to environmental changes, varying slightly across different cell types and tissues.