The fundamental component of cell membranes is the phospholipid bilayer. Phospholipids consist of hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails. This unique structure allows cell membranes to maintain a barrier between the cell's internal environment and the external surroundings while enabling selective permeability for substance transport. Additionally, various proteins embedded in the membrane play essential roles in communication, transport, and signal transduction. Understanding the structure and function of cell membranes is crucial for studying cellular processes and the overall physiology of organisms.