A wall, in a biological context, is a rigid structural component that provides mechanical support and protection to the cell membrane. In certain domains of life, this structure is composed of materials distinct from the plasma membrane, contributing significantly to the cell's overall shape and ability to withstand internal osmotic pressure. Chemically, the composition varies widely depending on the organism, incorporating elements such as cellulose, peptidoglycan, or silica. Functionally, the wall maintains cellular integrity, regulates cell volume, and often serves as a critical interface for external environmental interactions, thereby defining the physical boundaries of the living unit.