View source for Biology:Sperm

{{Short description|Male reproductive cell in anisogamous forms of sexual reproduction}}
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[[File:Complete diagram of a human spermatozoa en.svg|thumb|right|350px|Diagram of a human sperm cell]]

'''Sperm''' ({{plural form}}: '''sperm''' or '''sperms''') is the [[Biology:Male|male]] reproductive [[Biology:Cell|cell]], or [[Biology:Gamete|gamete]], in anisogamous forms of [[Biology:Sexual reproduction|sexual reproduction]] (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a [[Biology:Flagellum|flagellum]], which are known as spermatozoa, while some [[Biology:Red algae|red algae]] and [[Biology:Fungi|fungi]] produce non-motile sperm cells, known as '''spermatia'''.<ref>{{Cite web|url=https://www.collinsdictionary.com/dictionary/english/spermatium|title=Spermatium definition and meaning |website=Collins English Dictionary |language=en|access-date=2020-02-20}}</ref> [[Biology:Flowering plant|Flowering plant]]s contain non-motile sperm inside [[Biology:Pollen|pollen]], while some more basal plants like ferns and some [[Biology:Gymnosperm|gymnosperm]]s have motile sperm.<ref>{{Cite book|last=Kumar|first=Anil|url=https://books.google.com/books?id=HTdFYFNxnWQC&pg=PA261|title=Botany for Degree Gymnosperm|date=2006|publisher=S. Chand Publishing|isbn=978-81-219-2618-8|pages=261|language=en|edition=Multicolor}}</ref>

Sperm cells form during the process known as [[Biology:Spermatogenesis|spermatogenesis]], which in [[Biology:Amniote|amniote]]s ([[Biology:Reptile|reptile]]s and [[Biology:Mammal|mammal]]s) takes place in the seminiferous tubules of the testicles.<ref>{{Cite web|url=https://www.britannica.com/science/animal-reproductive-system|title=Animal reproductive system - Male systems|website=Encyclopedia Britannica|language=en|access-date=2020-02-20}}</ref> This process involves the production of several successive sperm cell precursors, starting with spermatogonia, which [[Biology:Cellular differentiation|differentiate]] into [[Biology:Spermatocyte|spermatocyte]]s. The spermatocytes then undergo [[Biology:Meiosis|meiosis]], reducing their [[Biology:Ploidy|chromosome number]] by half, which produces [[Biology:Spermatid|spermatid]]s. The spermatids then mature and, in animals, construct a tail, or flagellum, which gives rise to the mature, motile sperm cell. This whole process occurs constantly and takes around 3 months from start to finish.

Sperm cells cannot divide and have a limited lifespan, but after fusion with [[Biology:Egg cell|egg cell]]s during fertilization, a new organism begins developing, starting as a totipotent [[Biology:Zygote|zygote]]. The [[Biology:Human|human]] sperm cell is [[Biology:Haploid|haploid]], so that its 23 [[Biology:Chromosome|chromosome]]s can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. In mammals, sperm is stored in the epididymis and is released from the penis during [[Medicine:Ejaculation|ejaculation]] in a fluid known as [[Biology:Semen|semen]].

The word ''sperm'' is derived from the Greek word σπέρμα, ''sperma'', meaning "seed".

[[File:Human sperm under microscope.webm|thumb|Video of human sperm cells under a microscope]]

== Evolution ==
{{Main|Biology:Evolution of sexual reproduction}}

It is generally accepted that [[Biology:Isogamy|isogamy]] is the ancestor to sperm and eggs. However, there are no fossil records for the evolution of sperm and [[Biology:Egg cell|eggs]] from isogamy leading there to be a strong emphasis on mathematical models to understand the evolution of sperm.<ref>{{Cite book|last1=Pitnick|first1=Scott S.|url=https://books.google.com/books?id=kctYNbO1fE0C&q=sperm+biology+isogamy|title=Sperm Biology: An Evolutionary Perspective|last2=Hosken|first2=Dave J.|last3=Birkhead|first3=Tim R.|date=2008-11-21|publisher=Academic Press|isbn=978-0-08-091987-4|pages=43–44|language=en}}</ref>

A widespread hypothesis states that sperm evolved rapidly, but there is no direct evidence that sperm evolved at a fast rate or before other male characteristics.<ref>{{Cite journal|last1=Fitzpatrick|first1=John L.|last2=Bridge|first2=C. Daisy|last3=Snook|first3=Rhonda R.|date=2020-08-12|title=Repeated evidence that the accelerated evolution of sperm is associated with their fertilization function|journal=Proceedings of the Royal Society B: Biological Sciences|volume=287|issue=1932|pages=20201286|doi=10.1098/rspb.2020.1286|pmid=32752988|pmc=7575512}}</ref>

==Sperm in animals==
{{Further|Biology:Spermatozoon}}

===Function===

The main sperm function is to reach the ovum and fuse with it to deliver two sub-cellular structures: (i) the male [[Biology:Pronucleus|pronucleus]] that contains the genetic material and (ii) the [[Biology:Centriole|centriole]]s that are structures that help organize the [[Biology:Microtubule|microtubule]] [[Biology:Cytoskeleton|cytoskeleton]].{{clarification needed|reason=which organisms does this refer to?|date=April 2021}}

The nuclear DNA in sperm cells is [[Biology:Ploidy|haploid]], that is, they contribute only one copy of each paternal [[Biology:Chromosome|chromosome]] pair. [[Biology:Mitochondrion|Mitochondria]] in human sperm contain no or very little [[Biology:DNA|DNA]] because [[Biology:Mitochondrial DNA|mtDNA]] is degraded while sperm cells are maturing, hence they typically do not contribute any genetic material to their offspring.<ref>{{Cite journal |last=Lee |first=William |last2=Zamudio-Ochoa |first2=Angelica |last3=Buchel |first3=Gina |last4=Podlesniy |first4=Petar |last5=Marti Gutierrez |first5=Nuria |last6=Puigròs |first6=Margalida |last7=Calderon |first7=Anna |last8=Tang |first8=Hsin-Yao |last9=Li |first9=Li |last10=Mikhalchenko |first10=Aleksei |last11=Koski |first11=Amy |last12=Trullas |first12=Ramon |last13=Mitalipov |first13=Shoukhrat |last14=Temiakov |first14=Dmitry |date=October 2023 |title=Molecular basis for maternal inheritance of human mitochondrial DNA |url=https://www.nature.com/articles/s41588-023-01505-9 |journal=Nature Genetics |language=en |volume=55 |issue=10 |pages=1632–1639 |doi=10.1038/s41588-023-01505-9 |issn=1546-1718|pmc=10763495 }}</ref>

===Anatomy===
[[File:Sperm-egg.jpg|thumb|Sperm and egg fusing ([[Biology:Fertilisation|fertilisation]])]]
[[File:Sperm Head Dimensions.png|thumb|Dimensions of the human sperm head measured from a 39-year-old healthy human subject]]

The mammalian sperm cell can be divided in 2 parts connected by a neck:
* Head: contains the [[Biology:Cell nucleus|nucleus]] with densely coiled chromatin fibers, surrounded anteriorly by a thin, flattened sac called the [[Medicine:Acrosome|acrosome]], which contains enzymes used for penetrating the female egg. It also contains vacuoles.<ref>{{cite journal| pmc=4346294 | pmid=25780567 | doi=10.1186/2051-4190-23-3 | volume=23 | title=The nature of human sperm head vacuoles: a systematic literature review | year=2013 | journal=Basic Clin Androl | page=3 | last1 = Boitrelle | first1 = F | last2 = Guthauser | first2 = B | last3 = Alter | first3 = L | last4 = Bailly | first4 = M | last5 = Wainer | first5 = R | last6 = Vialard | first6 = F | last7 = Albert | first7 = M | last8 = Selva | first8 = J | doi-access=free }}</ref>
* Tail: also called the [[Biology:Flagellum|flagellum]], is the longest part and capable of wave-like motion that propels sperm for swimming and aids in the penetration of the egg.<ref>Fawcett, D. W. (1981) Sperm Flagellum. In: The Cell. D. W. Fawcett. Philadelphia, W. B. Saunders Company. 14:   pp. 604-640.</ref><ref>Lehti, M. S. and A. Sironen (2017). "Formation and function of sperm tail structures in association with sperm motility defects." Bi</ref><ref>{{cite journal | last1 = Ishijima | first1 = Sumio | last2 = Oshio | first2 = Shigeru | last3 = Mohri | first3 = Hideo | year = 1986 | title = ''Flagellar movement of human spermatozoa'' | journal = Gamete Research | volume = 13 | issue = 3| pages = 185–197 | doi = 10.1002/mrd.1120130302 }}</ref> The tail was formerly thought to move symmetrically in a [[Helix|helical shape]].{{anchor|midpiece}}
* Neck: also called connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole-like.<ref name="Fishman et al 2018">{{cite journal |doi=10.1038/s41467-018-04678-8 |pmid=29880810 |pmc=5992222 |title=A novel atypical sperm centriole is functional during human fertilization |journal=Nature Communications |volume=9 |issue=1 |pages=2210 |year=2018 |last1=Fishman |first1=Emily L |last2=Jo |first2=Kyoung |last3=Nguyen |first3=Quynh P. H |last4=Kong |first4=Dong |last5=Royfman |first5=Rachel |last6=Cekic |first6=Anthony R |last7=Khanal |first7=Sushil |last8=Miller |first8=Ann L |last9=Simerly |first9=Calvin |last10=Schatten |first10=Gerald |last11=Loncarek |first11=Jadranka |last12=Mennella |first12=Vito |last13=Avidor-Reiss |first13=Tomer |bibcode=2018NatCo...9.2210F }}</ref><ref>{{cite journal |doi=10.1534/genetics.109.101709 |pmid=19293139 |pmc=2674812 |title=A Proximal Centriole-Like Structure is Present in Drosophila Spermatids and Can Serve as a Model to Study Centriole Duplication |journal=Genetics |volume=182 |issue=1 |pages=133–44 |year=2009 |last1=Blachon |first1=S |last2=Cai |first2=X |last3=Roberts |first3=K. A |last4=Yang |first4=K |last5=Polyanovsky |first5=A |last6=Church |first6=A |last7=Avidor-Reiss |first7=T }}</ref> The ''midpiece'' has a central filamentous core with many mitochondria spiralled around it, used for [[Chemistry:Adenosine triphosphate|ATP]] production for the journey through the female [[Medicine:Cervix|cervix]], [[Biology:Uterus|uterus]], and oviducts.

During fertilization, the sperm provides three essential parts to the [[Biology:Oocyte|oocyte]]: (1) a signalling or activating factor, which causes the metabolically dormant oocyte to activate; (2) the haploid paternal [[Biology:Genome|genome]]; (3) the centriole, which is responsible for forming the [[Biology:Centrosome|centrosome]] and [[Biology:Microtubule|microtubule]] system.<ref>{{Cite book|chapter=The biology of fertilization in humans|editor1=Patrizio, Pasquale|title=A color atlas for human assisted reproduction: laboratory and clinical insights|publisher=Lippincott Williams & Wilkins|year=2003|isbn=978-0-7817-3769-2|page=3|chapter-url=https://books.google.com/books?id=2SBoQ8H-KMIC&pg=PA3|author1=Hewitson, Laura  |author2=Schatten, Gerald P. |name-list-style=amp |access-date=2013-11-09|display-editors=etal}}</ref>

===Origin===
The spermatozoa of [[Biology:Animal|animal]]s are produced through [[Biology:Spermatogenesis|spermatogenesis]] inside the male gonads (testicles) via meiotic division. The initial spermatozoon process takes around 70 days to complete. The process starts with the production of spermatogonia from [[Biology:Germ cell|germ cell]] precursors. These divide and differentiate into spermatocytes, which undergo meiosis to form [[Biology:Spermatid|spermatid]]s. In the spermatid stage, the sperm develops the familiar tail. The next stage where it becomes fully mature takes around 60 days when it is called a spermatozoan.<ref>[http://www.netdoctor.co.uk/menshealth/facts/semenandsperm.htm Semen and sperm quality]</ref> Sperm cells are carried out of the male body in a fluid known as [[Biology:Semen|semen]]. Human sperm cells can survive within the female reproductive tract for more than 5 days post coitus.<ref>{{cite journal | last1 = Gould | first1 = JE | last2 = Overstreet | first2 = JW | last3 = Hanson | first3 = FW | year = 1984 | title = Assessment of human sperm function after recovery from the female reproductive tract | journal = Biology of Reproduction | volume = 31 | issue = 5| pages = 888–894 | doi=10.1095/biolreprod31.5.888| pmid = 6518230 | doi-access = free }}</ref> Semen is produced in the seminal vesicles, prostate gland and urethral glands.

In 2016, scientists at Nanjing Medical University claimed they had produced cells resembling mouse spermatids from mouse embryonic stem cells artificially. They injected these spermatids into mouse eggs and produced pups.<ref name="Cyranoski 2016">{{cite journal |doi=10.1038/nature.2016.19453 |title=Researchers claim to have made artificial mouse sperm in a dish |journal=Nature |year=2016 |last1=Cyranoski |first1=David |s2cid=87014225 }}</ref>

===Sperm quality===
{{main|Medicine:Semen quality}}
[[File:Sperm stained.JPG|thumb|left|Human sperm [[Staining|stained]] for semen quality testing]]

Sperm quantity and quality are the main parameters in semen quality, which is a measure of the ability of semen to accomplish fertilization. Thus, in humans, it is a measure of fertility in a [[Biology:Man|man]]. The genetic quality of sperm, as well as its volume and motility, all typically [[Biology:Paternal age effect|decrease with age]].<ref name="About.com article by R. Gurevich">{{cite web|url=http://infertility.about.com/od/causesofinfertility/f/maleagefertile.htm|title=Does Age Affect Male Fertility?|last=Gurevich|first=Rachel|date=2008-06-10|publisher=About.com|access-date=14 February 2010|archive-date=2015-09-28|archive-url=https://web.archive.org/web/20150928014046/http://infertility.about.com/od/causesofinfertility/f/maleagefertile.htm|url-status=dead}}</ref>

DNA damages present in sperm cells in the period after meiosis but before fertilization may be repaired in the fertilized egg, but if not repaired, can have serious deleterious effects on fertility and the developing embryo. Human sperm cells are particularly vulnerable to free radical attack and the generation of oxidative DNA damage,<ref name="pmid26178844">{{cite book |vauthors=Gavriliouk D, Aitken RJ |title=The Male Role in Pregnancy Loss and Embryo Implantation Failure |chapter=Damage to Sperm DNA Mediated by Reactive Oxygen Species: Its Impact on Human Reproduction and the Health Trajectory of Offspring |volume=868 |pages=23–47 |year=2015 |pmid=26178844 |doi=10.1007/978-3-319-18881-2_2 |series=Advances in Experimental Medicine and Biology |isbn=978-3-319-18880-5 }}</ref> such as that from [[Chemistry:8-Oxo-2'-deoxyguanosine|8-Oxo-2'-deoxyguanosine]].

The postmeiotic phase of mouse spermatogenesis is very sensitive to environmental genotoxic agents, because as male germ cells form mature sperm they progressively lose the ability to repair DNA damage.<ref name="pmid18282746">{{cite journal |vauthors=Marchetti F, Wyrobek AJ |title=DNA repair decline during mouse spermiogenesis results in the accumulation of heritable DNA damage |journal=DNA Repair |volume=7 |issue=4 |pages=572–81 |year=2008 |pmid=18282746 |doi=10.1016/j.dnarep.2007.12.011 |s2cid=1316244 |url=https://digital.library.unt.edu/ark:/67531/metadc895292/}}</ref> Irradiation of male mice during late spermatogenesis can induce damage that persists for at least 7 days in the fertilizing sperm cells, and disruption of maternal DNA double-strand break repair pathways increases sperm cell-derived chromosomal aberrations.<ref name="pmid17978187">{{cite journal |vauthors=Marchetti F, Essers J, Kanaar R, Wyrobek AJ |title=Disruption of maternal DNA repair increases sperm-derived chromosomal aberrations |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=104 |issue=45 |pages=17725–9 |year=2007 |pmid=17978187 |pmc=2077046 |doi=10.1073/pnas.0705257104 |bibcode=2007PNAS..10417725M |doi-access=free }}</ref> Treatment of male mice with [[Chemistry:Melphalan|melphalan]], a bifunctional alkylating agent frequently employed in chemotherapy, induces DNA lesions during meiosis that may persist in an unrepaired state as germ cells progress through DNA repair-competent phases of spermatogenic development.<ref name="pmid25567288">{{cite journal |vauthors=Marchetti F, Bishop J, Gingerich J, Wyrobek AJ |title=Meiotic interstrand DNA damage escapes paternal repair and causes chromosomal aberrations in the zygote by maternal misrepair |journal=Scientific Reports |volume=5 |page=7689 |year=2015 |pmid=25567288 |pmc=4286742 |doi=10.1038/srep07689 |bibcode=2015NatSR...5E7689M }}</ref> Such unrepaired DNA damages in sperm cells, after fertilization, can lead to offspring with various abnormalities.

=== Sperm size ===
Related to sperm quality is sperm size, at least in some animals. For instance, the sperm of some species of fruit fly (''[[Biology:Drosophila|Drosophila]]'') are up to 5.8&nbsp;cm long—about 20 times as long as the fly itself. Longer sperm cells are better than their shorter counterparts at displacing competitors from the female's seminal receptacle. The benefit to females is that only healthy males carry "good" genes that can produce long sperm in sufficient quantities to outcompete their competitors.<ref>{{cite journal |doi=10.1038/nature18005 |pmid=27225128 |title=How sexual selection can drive the evolution of costly sperm ornamentation |journal=Nature |volume=533 |issue=7604 |pages=535–8 |year=2016 |last1=Lüpold |first1=Stefan |last2=Manier |first2=Mollie K |last3=Puniamoorthy |first3=Nalini |last4=Schoff |first4=Christopher |last5=Starmer |first5=William T |last6=Luepold |first6=Shannon H. Buckley |last7=Belote |first7=John M |last8=Pitnick |first8=Scott |bibcode=2016Natur.533..535L |s2cid=4407752 |url=https://zenodo.org/record/1000843 }}</ref><ref>{{cite journal |doi=10.1038/533476a |pmid=27225117 |title=The bigger, the better |journal=Nature |volume=533 |issue=7604 |pages=476 |year=2016 |last1=Gardiner |first1=Jennifer R |doi-access=free }}</ref>

===Market for human sperm===

Some [[Biology:Sperm bank|sperm bank]]s hold up to {{convert|170|L}} of sperm.<ref>{{cite news |author=Sarfraz Manzoor |date=2 November 2012 |url=https://www.theguardian.com/society/2012/nov/02/worlds-biggest-sperm-bank-denmark |title=Come inside: the world's biggest sperm bank |newspaper=The Guardian |access-date=4 August 2013}}</ref>

In addition to [[Medicine:Ejaculation|ejaculation]], it is possible to extract sperm through [[Medicine:Testicular sperm extraction|testicular sperm extraction]].

On the global market, {{wipe|Denmark}} has a well-developed system of human sperm export. This success mainly comes from the reputation of Danish sperm donors for being of high quality<ref name=ncbio/> and, in contrast with the law in the other Nordic countries, gives donors the choice of being either anonymous or non-anonymous to the receiving couple.<ref name=ncbio>[http://www.norden.org/da/publikationer/publikationer/2006-505/at_download/publicationfile Assisted Reproduction in the Nordic Countries] {{Webarchive|url=https://web.archive.org/web/20131111135230/http://www.norden.org/da/publikationer/publikationer/2006-505/at_download/publicationfile |date=2013-11-11 }} ncbio.org</ref> Furthermore, Nordic sperm donors tend to be tall and highly educated<ref name=newser>[http://www.newser.com/story/34788/fda-rules-block-import-of-prized-danish-sperm.html FDA Rules Block Import of Prized Danish Sperm] Posted Aug 13, 08 7:37 AM CDT in World, Science & Health</ref> and have altruistic motives for their donations,<ref name=newser/> partly due to the relatively low monetary compensation in Nordic countries. More than 50 countries worldwide are importers of Danish sperm, including Paraguay, {{wipe|Canada}}, Kenya, and [[Place:Hong Kong|Hong Kong]].<ref name=ncbio/> However, the [[Organization:Food and Drug Administration|Food and Drug Administration]] (FDA) of the US has banned import of any sperm, motivated by a risk of transmission of [[Medicine:Creutzfeldt–Jakob disease|Creutzfeldt–Jakob disease]], although such a risk is insignificant, since artificial insemination is very different from [[Medicine:Creutzfeldt–Jakob disease#Transmission|the route of transmission of Creutzfeldt–Jakob disease]].<ref name=kotler>{{cite news |author=Steven Kotler |date=26 September 2007  |url=http://www.laweekly.com/news/the-god-of-sperm-2150560 |title=The God of Sperm}}</ref> The prevalence of Creutzfeldt–Jakob disease for donors is at most one in a million, and if the donor was a carrier, the infectious proteins would still have to cross the blood-testis barrier to make transmission possible.<ref name=kotler/>

===History===
Sperm were first observed in 1677 by [[Biography:Antonie van Leeuwenhoek|Antonie van Leeuwenhoek]]<ref>{{cite news|url=http://www.cbc.ca/news2/background/genetics_reproduction/timeline.html|title=Timeline: Assisted reproduction and birth control|access-date=2006-04-06 | work=CBC News}}</ref> using a [[Engineering:Microscope|microscope]]. He described them as being [[Biology:Animalcule|animalcule]]s (little animals), probably due to his belief in [[Philosophy:Preformationism|preformationism]], which thought that each sperm contained a fully formed but small human.{{citation needed|date=January 2011}}

===Forensic analysis===
Ejaculated fluids are detected by ultraviolet light, irrespective of the structure or colour of the surface.<ref>{{cite journal |doi=10.2174/1874402800801010012 |title=Detection of Semen (Human and Boar) and Saliva on Fabrics by a Very High Powered UV-/VIS-Light Source |journal=The Open Forensic Science Journal |volume=1 |pages=12–15 |year=2008 |last1=Fiedler |first1=Anja |last2=Rehdorf |first2=Jessica |last3=Hilbers |first3=Florian |last4=Johrdan |first4=Lena |last5=Stribl |first5=Carola |last6=Benecke |first6=Mark |doi-access=free }}</ref> Sperm heads, e.g. from vaginal swabs, are still detected by [[Biology:Microscopy|microscopy]] using the "Christmas Tree Stain" method, i.e., Kernechtrot-Picroindigocarmine (KPIC) staining.<ref>{{cite journal |pmid=11305439 |year=2001 |last1=Allery |first1=J. P |title=Cytological detection of spermatozoa: Comparison of three staining methods |journal=Journal of Forensic Sciences |volume=46 |issue=2 |pages=349–51 |last2=Telmon |first2=N |last3=Mieusset |first3=R |last4=Blanc |first4=A |last5=Rougé |first5=D |doi=10.1520/JFS14970J }}</ref><ref>{{cite web|url=http://static.dna.gov/lab-manual/Linked%20Documents/Protocols/pdi_lab_pro_2.05.pdf|title=The Presidents's DNA Initiative: Semen Stain Identification: Kernechtrot|author=Illinois State Police/President's DNA Initiative|access-date=2009-12-10|archive-date=2016-12-26|archive-url=https://web.archive.org/web/20161226223420/https://static.dna.gov/lab-manual/Linked%20Documents/Protocols/pdi_lab_pro_2.05.pdf|url-status=dead}}</ref>

==Sperm in plants==
Sperm cells in algal and many plant [[Biology:Gametophyte|gametophyte]]s are produced in male gametangia (antheridia) via mitotic division. In [[Biology:Flowering plant|flowering plant]]s, sperm nuclei are produced inside [[Biology:Pollen|pollen]].<ref name="MokwalaMangena2018">{{cite book|author1=Phatlane William Mokwala|author2=Phetole Mangena|title=Pollination in Plants|url=https://books.google.com/books?id=fS6RDwAAQBAJ|date=6 June 2018|publisher=BoD – Books on Demand|isbn=978-1-78923-236-3|page=8}}</ref>

==Motile sperm cells==
[[File:Plant sperm.png|thumb|Motile sperm cells of [[Biology:Algae|algae]] and seedless plants<ref name="Raven">{{cite book | last = Raven | first = Peter H. |author2=Ray F. Evert |author3=Susan E. Eichhorn | title = Biology of Plants, 7th Edition | publisher = W.H. Freeman and Company Publishers | year = 2005 | location = New York | isbn = 0-7167-1007-2}}</ref>]]

Motile sperm cells typically move via flagella and require a water medium in order to swim toward the egg for fertilization. In animals most of the energy for sperm motility is derived from the metabolism of [[Chemistry:Fructose|fructose]] carried in the seminal fluid. This takes place in the [[Biology:Mitochondria|mitochondria]] located in the sperm's midpiece (at the base of the sperm head). These cells cannot swim backwards due to the nature of their propulsion. The uniflagellated sperm cells (with one flagellum) of [[Biology:Animal|animal]]s are referred to as spermatozoa, and are known to vary in size.{{citation needed|date=January 2011}}

Motile sperm are also produced by many [[Biology:Protist|protist]]s and the gametophytes of [[Biology:Bryophyte|bryophyte]]s, [[Biology:Fern|fern]]s and some [[Biology:Gymnosperm|gymnosperm]]s such as [[Biology:Cycad|cycad]]s and [[Biology:Ginkgo|ginkgo]]. The sperm cells are the only flagellated cells in the life cycle of these plants. In many ferns and [[Biology:Lycophyte|lycophyte]]s, cycads and ginkgo they are multi-flagellated (carrying more than one flagellum).<ref name="Raven"/>

In [[Biology:Nematode|nematode]]s, the sperm cells are [[Biology:Amoeboid movement|amoeboid]] and crawl, rather than swim, towards the egg cell.<ref name="Bottino">{{cite journal |author=Bottino D, Mogilner A, Roberts T, Stewart M, Oster G |title=How nematode sperm crawl |journal=Journal of Cell Science |volume=115 |issue=Pt 2 |pages=367–84 |year=2002 |doi=10.1242/jcs.115.2.367 |pmid=11839788 }}</ref>

==Non-motile sperm cells==
Non-motile sperm cells called '''spermatia''' lack flagella and therefore cannot swim. Spermatia are produced in a [[Biology:Gametangium|spermatangium]].<ref name="Raven"/>

Because spermatia cannot swim, they depend on their environment to carry them to the egg cell. Some red algae, such as ''[[Biology:Polysiphonia|Polysiphonia]]'', produce non-motile spermatia that are spread by water currents after their release.<ref name="Raven"/> The spermatia of [[Biology:Rust (fungus)|rust fungi]] are covered with a sticky substance. They are produced in flask-shaped structures containing [[Biology:Nectar|nectar]], which attract [[Biology:Fly|flies]] that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in [[Biology:Flowering plant|flowering plant]]s.<ref name="Sumbali">{{cite book | last = Sumbali| first = Geeta | title = The Fungi | publisher = Alpha Science Int'l Ltd. | year = 2005 | isbn = 1-84265-153-6}}</ref>

Fungal spermatia (also called pycniospores, especially in the Uredinales) may be confused with conidia. Conidia are [[Biology:Spore|spore]]s that germinate independently of fertilization, whereas spermatia are [[Biology:Gamete|gamete]]s that are required for fertilization. In some fungi, such as ''[[Biology:Neurospora crassa|Neurospora crassa]]'', spermatia are identical to microconidia as they can perform both functions of fertilization as well as giving rise to new organisms without fertilization.<ref name="Maheshwari">{{cite journal |author=Maheshwari R |title=Microconidia of Neurospora crassa |journal=Fungal Genetics and Biology |volume=26 |issue=1 |pages=1–18 |year=1999 |pmid=10072316 |doi=10.1006/fgbi.1998.1103}}</ref>

==Sperm nuclei==
In almost all [[Biology:Embryophyte|embryophyte]]s, including most gymnosperms and all [[Biology:Angiosperm|angiosperm]]s, the male gametophytes ([[Biology:Pollen|pollen]] grains) are the primary mode of [[Biology:Biological dispersal|dispersal]], for example via wind or insect [[Biology:Pollination|pollination]], eliminating the need for water to bridge the gap between male and female. Each pollen grain contains a spermatogenous (generative) cell. Once the pollen lands on the stigma of a receptive flower, it germinates and starts growing a [[Biology:Pollen tube|pollen tube]] through the carpel. Before the tube reaches the [[Biology:Ovule|ovule]], the nucleus of the generative cell in the pollen grain divides and gives rise to two sperm nuclei, which are then discharged through the tube into the ovule for fertilization.<ref name="Raven"/>

In some [[Biology:Protist|protist]]s, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization tube. Oomycetes form sperm nuclei in a [[Biology:Syncytium|syncytical]] antheridium surrounding the egg cells. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants.<ref name="Raven"/>

==Sperm centrioles==

Most sperm cells have centrioles in the sperm neck.<ref>{{cite journal| pmc=4381714 | pmid=25883936 | doi=10.3389/fcell.2015.00021 | volume=3 | title=Atypical centrioles during sexual reproduction | year=2015 | journal=Front Cell Dev Biol | page=21 | last1 = Avidor-Reiss | first1 = T | last2 = Khire | first2 = A | last3 = Fishman | first3 = EL | last4 = Jo | first4 = KH| doi-access=free }}</ref> Sperm of many animals has two typical centrioles, known as the proximal centriole and distal centriole. Some animals (including humans and bovines) have a single typical centriole, the proximal centriole, as well as a second centriole with atypical structure.<ref name="Fishman et al 2018" /> Mice and rats have no recognizable sperm centrioles. The fruit fly ''[[Biology:Drosophila melanogaster|Drosophila melanogaster]]'' has a single centriole and an atypical centriole named the proximal centriole-like.<ref>{{cite journal | date = May 2009 | title =  A Proximal Centriole-Like Structure Is Present in Drosophila Spermatids and Can Serve as a Model to Study Centriole Duplication| journal = Genetics | volume = 182 | issue = 1| pages = 133–44 | doi = 10.1534/genetics.109.101709  | pmid =  19293139| last1 = Blachon | first1 = S. | last2 = Cai | first2 = X. | last3 = Roberts | first3 = K. A. | last4 = Yang | first4 = K. | last5 = Polyanovsky | first5 = A. | last6 = Church | first6 = A. | last7 = Avidor-Reiss | first7 = T.| pmc = 2674812 }}</ref>

== Sperm tail formation ==
The sperm tail is a specialized type of [[Biology:Cilium|cilium]] (aka flagella). In many animals the sperm tail is formed through the unique process of [[Biology:Cytosolic ciliogenesis|cytosolic ciliogenesis]], in which all or part of the sperm tail's [[Biology:Axoneme|axoneme]] is formed in the [[Biology:Cytoplasm|cytoplasm]] or gets exposed to the cytoplasm.<ref name="Avidor-Reiss & Leroux 2015">{{cite journal |doi=10.1016/j.cub.2015.11.001 |pmid=26654377 |pmc=5857621 |title=Shared and Distinct Mechanisms of Compartmentalized and Cytosolic Ciliogenesis |journal=Current Biology |volume=25 |issue=23 |pages=R1143–50 |year=2015 |last1=Avidor-Reiss |first1=Tomer |last2=Leroux |first2=Michel R }}</ref>

==See also==
* List of distinct cell types in the adult human body
* [[Biology:Female sperm|Female sperm]]
* [[Biology:Female sperm storage|Female sperm storage]]
* [[Biology:Mendelian inheritance|Mendelian inheritance]]
* [[Biology:Polyspermy|Polyspermy]]
* [[Philosophy:Sperm competition|Sperm competition]]
* Sperm granuloma
* [[Social:Sperm theft|Sperm theft]]
* List of distinct cell types in the adult human body

== Citations ==
{{Reflist|35em}}

== General and cited sources ==
* Fawcett, D. W. (1981). "Sperm Flagellum". In: D. W. Fawcett. [https://archive.org/details/cell0000fawc/mode/2up ''The Cell'', 2nd ed] {{Registration required}}. Philadelphia: W. B. Saunders Company. [https://archive.org/details/cell0000fawc/page/604/mode/2up pp.&nbsp;604–640] {{Registration required}}. {{Isbn|9780721635842}}. {{Oclc|993416586}}.
* Lehti, M. S. and A. Sironen (October 2017). [https://academic.oup.com/biolreprod/article/97/4/522/4097575 "Formation and function of sperm tail structures in association with sperm motility defects"]. ''Biol Reprod'' 97(4): 522–536. {{doi|10.1093/biolre/iox096}}.

==External links==
* [https://www.youtube.com/watch?v=vvnEsOaKxuw&NR=1 Human Sperm Under a Microscope]

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{{Succession box|title=Stages of human development|before=None|after=[[Biology:Zygote|Zygote]]|years=Sperm + [[Biology:Oocyte|Oocyte]]}}
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[[Category:Germ cells]]
[[Category:Reproductive system]]

{{Sourceattribution|Sperm}}