Editing Alkane (section)

===Biological occurrence===
[[Image:Rotbuntes Rind.jpg|thumb|right|[[Methanogen]]ic [[archaea]] in the gut of cows produce [[methane]].]]
Aside from petroleum and natural gas, alkanes occur significantly in nature only as methane, which is produced by some [[archaea]] by the process of [[methanogenesis]].  These organisms are found in the gut of termites<ref>{{Cite journal |last1=Buczkowski|first1=Grzegorz|last2=Bertelsmeier|first2=Cleo|date=15 January 2017|title=Invasive termites in a changing climate: A global perspective|journal=Ecology and Evolution |volume=7|issue=3 |pages=974–985|doi=10.1002/ece3.2674|pmc=5288252|pmid=28168033|bibcode=2017EcoEv...7..974B }}</ref> and cows.<ref>{{Cite news |url=https://gizmodo.com/do-cow-farts-actually-contribute-to-global-warming-1562144730|title=Do Cow Farts Actually Contribute to Global Warming?|work=TodayIFoundOut.com|first=Matt|last=Blitz|via=Gizmodo |access-date=11 April 2018|language=en-US}}</ref>  The [[methane]] is produced from [[carbon dioxide]] or other organic compounds. Energy is released by the oxidation of [[hydrogen]]:
:CO<sub>2</sub> + 4&nbsp;H<sub>2</sub> → CH<sub>4</sub> + 2&nbsp;H<sub>2</sub>O
It is probable that our current deposits of natural gas were formed in a similar way.<ref>{{Cite news|url=https://education.nationalgeographic.org/resource/natural-gas|title=Natural Gas|work=Resources Library|publisher=National Geographic Society|access-date=11 April 2018|language=en}}</ref>


Certain types of bacteria can metabolize alkanes: they prefer even-numbered carbon chains as they are easier to degrade than odd-numbered chains.<ref>{{Cite web|url=http://equilibrator.weizmann.ac.il/static/classic_rxns/classic_reactions/fatty_acid_met.html|title=Metabolism of Alkanes and Fatty Acids – eQuilibrator 0.2 beta documentation|website=equilibrator.weizmann.ac.il|language=en|access-date=11 April 2018}}</ref>

Alkanes play a negligible role in higher organisms, with rare exception.
Some yeasts, e.g., ''Candida tropicale'', ''[[Pichia]]'' sp., ''[[Rhodotorula]]'' sp., can use alkanes as a source of carbon or energy. The fungus ''[[Amorphotheca resinae]]'' prefers the longer-chain alkanes in [[aviation fuel]], and can cause serious problems for aircraft in tropical regions.<ref name=Hendey>{{cite journal | last1 = Hendey | first1 = N. I. | year = 1964 | title = Some observations on ''Cladosporium resinae'' as a fuel contaminant and its possible role in the corrosion of aluminium alloy fuel tanks | journal = Transactions of the British Mycological Society | volume = 47 | issue = 7| pages = 467–475 | doi=10.1016/s0007-1536(64)80024-3}}</ref>

In plants, the solid long-chain alkanes are found in the [[plant cuticle]] and [[epicuticular wax]] of many species, but are only rarely major constituents.<ref name=Baker1982>{{cite book |first=E.A.|last=Baker |date=1982 |chapter=Chemistry and morphology of plant epicuticular waxes |pages=139–165 |title=The Plant Cuticle |editor-first=D.F. |editor-last=Cutler |editor2-first=K.L. |editor2-last=Alvin  |editor3-first=C.E. |editor3-last=Price |publisher=Academic Press |isbn=0-12-199920-3}}</ref> They protect the plant against water loss, prevent the [[Leaching (agriculture)|leaching]] of important minerals by the rain, and protect against bacteria, fungi, and harmful insects. The carbon chains in plant alkanes are usually odd-numbered, between 27 and 33 carbon atoms in length,<ref name=Baker1982/> and are made by the plants by [[decarboxylation]] of even-numbered [[fatty acid]]s. The exact composition of the layer of wax is not only species-dependent but also changes with the season and such environmental factors as lighting conditions, temperature or humidity.<ref name=Baker1982/>

The [[Jeffrey pine]] is noted for producing exceptionally high levels of [[Heptane|''n''-heptane]] in its resin, for which reason its distillate was designated as the zero point for one [[octane rating]]. Floral scents have also long been known to contain volatile alkane components, and [[Nonane|''n''-nonane]] is a significant component in the scent of some [[rose]]s.<ref>{{cite journal | last1 = Kim | first1 =HyunJung | last2=Kim | first2=NamSun | last3=Lee | first3=DongSun | year =  2000 | title = Determination of floral fragrances of Rosa hybrida using solid-phase trapping-solvent extraction and gas chromatography–mass spectrometry. | journal = Journal of Chromatography A | volume = 902 | issue = 2| pages =  389–404 | doi = 10.1016/S0021-9673(00)00863-3 | pmid =11192171 }}</ref> Emission of gaseous and volatile alkanes such as [[ethane]], [[pentane]], and [[hexane]] by plants has also been documented at low levels, though they are not generally considered to be a major component of biogenic air pollution.<ref>{{cite journal | last1 = Kesselmeier | first1 = J. | last2 = Staudt | first2 = N. | year = 1999 | title = Biogenic Volatile Organic Compounds (VOC): An Overview on Emission, Physiology and Ecology | url = http://www.geo.uni-frankfurt.de/iau/epos/Gruppenintern/Kesselmeier___Staudt_JAC_1999.pdf | journal = Journal of Atmospheric Chemistry | volume = 33 | issue = 1 | pages = 22–38 | url-status = dead | archive-url = https://www.webcitation.org/6F5FQG2OP?url=http://www.geo.uni-frankfurt.de/iau/epos/Gruppenintern/Kesselmeier___Staudt_JAC_1999.pdf | archive-date = 13 March 2013| doi = 10.1023/A:1006127516791 | bibcode = 1999JAtC...33...23K | s2cid = 94021819 }}</ref>

Edible vegetable oils also typically contain small fractions of biogenic alkanes with a wide spectrum of carbon numbers, mainly 8 to 35, usually peaking in the low to upper 20s, with concentrations up to dozens of milligrams per kilogram (parts per million by weight) and sometimes over a hundred for the total alkane fraction.<ref>{{cite journal | last1 = Moreda
 | first1 =W. | last2=Perez-Camino | first2=M. C. |last3=Cert| first3=A.| year = 2001 | title = Gas and liquid chromatography of hydrocarbons in edible vegetable oils | journal = Journal of Chromatography A | volume = 936 | issue =1–2 | pages = 159–171 | doi=10.1016/s0021-9673(01)01222-5| pmid =11760997 | url=https://www.researchgate.net/publication/11596797}}</ref>

Alkanes are found in animal products, although they are less important than unsaturated hydrocarbons. One example is the shark liver oil, which is approximately 14% [[pristane]] (2,6,10,14-tetramethylpentadecane, C<sub>19</sub>H<sub>40</sub>). They are important as [[pheromone]]s, chemical messenger materials, on which insects depend for communication. In some species, e.g. the support beetle ''[[Xylotrechus colonus]]'', [[pentacosane]] (C<sub>25</sub>H<sub>52</sub>), 3-methylpentaicosane (C<sub>26</sub>H<sub>54</sub>) and 9-methylpentaicosane (C<sub>26</sub>H<sub>54</sub>) are transferred by body contact. With others like the [[tsetse fly]] ''Glossina morsitans morsitans'', the pheromone contains the four alkanes 2-methylheptadecane (C<sub>18</sub>H<sub>38</sub>), 17,21-dimethylheptatriacontane (C<sub>39</sub>H<sub>80</sub>), 15,19-dimethylheptatriacontane (C<sub>39</sub>H<sub>80</sub>) and 15,19,23-trimethylheptatriacontane (C<sub>40</sub>H<sub>82</sub>), and acts by smell over longer distances. [[waggle dance|Waggle-dancing]] [[honey bee]]s produce and release two alkanes, tricosane and pentacosane.<ref>{{cite journal |vauthors=Thom C, Gilley DC, Hooper J, Esch HE |date=21 August 2007 |title=The Scent of the Waggle Dance |journal=PLOS Biology |volume=5 |issue=9| page=e228 |doi=10.1371/journal.pbio.0050228 |pmid=17713987 |pmc=1994260 |doi-access=free }}</ref>