Cellwall

A cell wall is a rigid or semi-rigid layer that surrounds the plasma membrane in many organisms, including plants, fungi, bacteria, algae, and most archaea. It provides structural support, protection, and helps determine cell shape. The wall is external to the plasma membrane but remains porous enough to allow water and small molecules to pass.

Composition and diversity vary by lineage. In plants, the primary wall is rich in cellulose microfibrils within a matrix of hemicelluloses and pectins; some cells develop a thicker secondary wall inside the primary wall, often containing lignin for extra rigidity. The middle lamella, rich in pectins, glues adjacent cells together. Bacterial walls are mainly peptidoglycan; Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thinner layer plus an outer membrane. Fungal walls are primarily chitin with glucans and glycoproteins. Algal walls are diverse and may include cellulose, glycoproteins, minerals, or silica; some algae and many archaea have different compositions or lack walls.

Functions include maintaining cell shape and providing mechanical strength to resist turgor pressure, as well as protection from physical and osmotic stress. The wall also influences permeability and mediates intercellular communication in plants via plasmodesmata that traverse cell walls. Growth occurs through regulated loosening and expansion of wall networks, coordinated with cell elongation and division. Wall synthesis and remodeling involve secreted polymers and remodeling enzymes, such as expansins in plants and various hydrolases in microbes.

Understanding cell walls is important in plant biology, microbiology, and medicine, affecting nutrient exchange, pathogen interactions, and the action of antimicrobial agents.