A cell wall is a rigid, non-living layer found outside the plasma membrane of certain types of cells, providing structural integrity and protection to the cell contents. While the composition varies significantly depending on the domain of life, major components include cellulose in plant cell walls, chitin in the cell walls of many fungi, and peptidoglycan in bacterial cells. The primary functions of this external structure involve maintaining turgor pressure, providing mechanical strength, and acting as a barrier against external threats. The structural makeup and formation of the cell wall are fundamental biological processes that define the physical properties of the organism.