Editing Cell wall (section)

==Other cell coverings==

Many [[protist]]s and [[bacteria]] produce other cell surface structures apart from cell walls, external ([[extracellular matrix]]) or internal.<ref>{{cite book | vauthors = Preisig HR | chapter = Terminology and nomenclature of protist cell surface structures | title = The Protistan Cell Surface | pages = 1–28 | edition = Protoplasma special | date = 1994 | doi = 10.1007/978-3-7091-9378-5_1 | isbn = 978-3-7091-9380-8 }}</ref><ref>{{cite book | vauthors = Becker B | chapter = The cell surface of flagellates. | chapter-url = http://www.uni-koeln.de/math-nat-fak/botanik/bot1/AGBecker/Publikationen/Cell%20Surfaces%20of%20Flagellates/CELLSURFACE.htm | title = The Flagellates. Unity, diversity and evolution | veditors = Leadbeater BS, Green JC | publisher = Taylor and Francis | location = London | year = 2000 | archive-url = https://web.archive.org/web/20130212024846/http://www.uni-koeln.de/math-nat-fak/botanik/bot1/AGBecker/Publikationen/Cell%20Surfaces%20of%20Flagellates/CELLSURFACE.htm | archive-date = 2013-02-12 }}</ref><ref>{{cite book | last1 = Barsanti | first1 = Laura | last2 = Gualtieri | first2 = Paolo | name-list-style = vanc | date = 2006 | title = Algae: anatomy, biochemistry, and biotechnology | location = Florida, USA | publisher = CRC Press }}</ref> Many [[algae]] have a sheath or envelope of [[mucilage]] outside the cell made of [[exopolysaccharides]]. [[Diatom]]s build a [[frustule]] from [[silica]] extracted from the surrounding water; [[radiolarian]]s, [[foraminiferan]]s, [[testate amoebae]] and [[silicoflagellate]]s also produce a skeleton from [[mineral]]s, called [[test (biology)|test]] in some groups. Many [[green algae]], such as ''[[Halimeda]]'' and the [[Dasycladales]], and some [[red algae]], the [[Corallinales]], encase their cells in a [[secreted]] skeleton of [[calcium carbonate]]. In each case, the wall is rigid and essentially [[inorganic]]. It is the non-living component of cell. Some [[golden algae]], [[ciliate]]s and [[choanoflagellate]]s produces a shell-like protective outer covering called [[lorica (biology)|lorica]]. Some [[dinoflagellate]]s have a [[theca]] of [[cellulose]] plates, and [[coccolithophorid]]s have [[coccolith]]s.

An [[extracellular matrix]] (ECM) is also present in [[metazoans]]. Its [[Chemical composition|composition]] varies between cells, but [[collagen]]s are the most [[abundance (chemistry)|abundant]] protein in the ECM.<ref>{{cite journal | vauthors = Frantz C, Stewart KM, Weaver VM | title = The extracellular matrix at a glance | journal = Journal of Cell Science | volume = 123 | issue = Pt 24 | pages = 4195–200 | date = December 2010 | pmid = 21123617 | pmc = 2995612 | doi = 10.1242/jcs.023820 }}</ref><ref>{{cite book|last1=Alberts |first1=Bruce | first2 = Alexander | last2 = Johnson | first3 = Julian | last3 = Lewis | first4 = Martin | last4 = Raff | first5 = Keith | last5 = Roberts | first6 = Peter | last6 = Walter | name-list-style = vanc |title=Molecular biology of the cell|date=2002|publisher=Garland|location=New York |isbn=978-0-8153-4072-0 |pages = 1065 |edition=4th}}</ref>