Editing Period 5 element (section)

==Biological role==

Rubidium, strontium, yttrium, zirconium, and niobium have no biological role.  Yttrium can cause lung disease in humans.

Molybdenum-containing enzymes are used as catalysts by some bacteria to break the [[chemical bond]] in atmospheric molecular [[nitrogen]], allowing biological [[nitrogen fixation]]. At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Owing to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms ([[eukaryotes]]), though not in all bacteria.

Technetium, ruthenium, rhodium, palladium, and silver have no biological role.  Although cadmium has no known biological role in higher organisms, a cadmium-dependent [[carbonic anhydrase]] has been found in marine [[diatom]]s. Rats fed a tin-free diet exhibited improper growth, but the evidence for essentiality is otherwise limited.<ref name=essentialmetals>{{cite journal |last1=Zoroddu |first1=Maria Antonietta |last2=Aaseth |first2=Jan |first3=Guido |last3=Crisponi |first4=Serenella |last4=Medici |first5=Massimiliano |last5=Peana |first6=Valeria Marina |last6=Nurchi |date=2019 |title=The essential metals for humans: a brief overview |url= |journal=Journal of Inorganic Biochemistry |volume=195 |issue= |pages=120–129 |doi=10.1016/j.jinorgbio.2019.03.013 |pmid=30939379 |access-date=}}</ref><ref name="hdl.handle.net">Ultratrace minerals. Authors: Nielsen, Forrest H. USDA, ARS Source: Modern nutrition in health and disease / editors, Maurice E. Shils ... et al.. Baltimore : Williams & Wilkins, c1999., p. 283-303. Issue Date: 1999 URI: [http://hdl.handle.net/10113/46493]</ref> Indium has no biological role and can be toxic as well as antimony.

Tellurium has no biological role, although fungi can incorporate it in place of sulfur and selenium into [[amino acid]]s such as [[tellurocysteine]] and [[telluromethionine]].<ref name="tellurium-fungi">{{Cite journal|doi = 10.1007/BF02917437|title = Incorporation of tellurium into amino acids and proteins in a tellurium-tolerant fungi|year = 1989|last1 = Ramadan|first1 = Shadia E.|last2 = Razak|first2 = A. A.|last3 = Ragab|first3 = A. M.|last4 = El-Meleigy|first4 = M.|journal = Biological Trace Element Research|volume = 20|pages = 225–32|pmid = 2484755|issue = 3| bibcode=1989BTER...20..225R |s2cid = 9439946}}</ref> In humans, tellurium is partly metabolized into [[dimethyl telluride]], (CH<sub>3</sub>)<sub>2</sub>Te, a gas with a [[garlic]]-like odor which is exhaled in the breath of victims of tellurium toxicity or exposure.

Iodine is the heaviest [[essential element]] utilized widely by life in biological functions (only [[tungsten]], employed in enzymes by a few species of bacteria, is heavier). Iodine's rarity in many soils, due to initial low abundance as a crust-element, and also leaching of soluble iodide by rainwater, has led to many deficiency problems in land animals and inland human populations. [[Iodine deficiency]] affects about two billion people and is the leading preventable cause of [[intellectual disabilities]].<ref name="mcneil">{{Cite news|url=https://www.nytimes.com/2006/12/16/health/16iodine.html?fta=y|title=In Raising the World's I.Q., the Secret's in the Salt|last=McNeil|first=Donald G. Jr|date=2006-12-16|work=[[The New York Times]]|access-date=2008-12-04}}</ref>  Iodine is required by higher animals, which use it to synthesize [[thyroid hormones]], which contain the element. Because of this function, [[radioisotopes]] of iodine are concentrated in the [[thyroid gland]] along with nonradioactive iodine. The radioisotope [[iodine-131]], which has a high [[fission product yield]], concentrates in the thyroid, and is one of the most [[carcinogenic]] of [[nuclear fission]] products.

Xenon has no biological role, and is used as a [[General anaesthesia|general anaesthetic]].{{reflist|group=note}}