Cell wall

A rigid or semi-rigid layer outside a cell’s plasma membrane that supports and protects the cell. Its composition varies across organisms, with cellulose, chitin, and peptidoglycan among its major materials.

Cellulose: A structural polysaccharide made of glucose chains, abundant in plant cell walls. Cellulose microfibrils provide tensile strength to the walls of plants and many algae.
Turgor pressure: The pressure of a cell’s contents against its enclosing membrane or wall. Plant cell walls counter turgor pressure, helping cells remain firm without bursting.
Penicillin: A class of beta-lactam antibiotics that inhibit bacterial cell-wall synthesis. Penicillin weakens susceptible bacteria by disrupting construction of their peptidoglycan wall.
Plasma membrane: A selectively permeable lipid bilayer that encloses the cell’s cytoplasm. The membrane is universal among cells, whereas a cell wall lies outside it and is absent in some organisms.
Peptidoglycan: A mesh-like polymer of sugars and peptides that forms the bacterial cell wall. This distinctive polymer makes bacterial walls strong while allowing them to be remodeled during growth.
Cell expansion: An increase in cell volume, often driven by water uptake and controlled wall loosening. Plant cells expand when wall yielding allows turgor pressure to stretch the wall.
Lysozyme: An enzyme that breaks bonds in peptidoglycan and other bacterial cell-wall polysaccharides. Lysozyme can damage bacterial walls and occurs in secretions such as tears and saliva.
Archaeal cell envelope: The outer layers surrounding an archaeal cell, which may include a protein surface layer or other wall-like structures. Archaea have envelopes unlike bacterial peptidoglycan walls, despite often having a rigid outer layer.
Chitin: A nitrogen-containing polysaccharide found in fungal cell walls and arthropod exoskeletons. Fungi use chitin as a major load-bearing component of their walls.
Expansin: A plant protein that promotes cell-wall loosening without cutting the wall’s polysaccharide chains. Expansins help permit wall extension during growth.

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