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Do not fill this in! === Cells === {{main|Cell (biology)}} Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells by [[Cell division|division]].<ref>{{cite web |date=2 June 2019 |title=2.2: The Basic Structural and Functional Unit of Life: The Cell |url=https://med.libretexts.org/Courses/American_Public_University/APUS%3A_An_Introduction_to_Nutrition_(Byerley)/Text/03%3A_Nutrition_and_the_Human_Body/2.2%3A_The_Basic_Structural_and_Functional_Unit_of_Life%3A_The_Cell |url-status=live |archive-url=https://web.archive.org/web/20200329060227/https://med.libretexts.org/Courses/American_Public_University/APUS:_An_Introduction_to_Nutrition_(Byerley)/Text/03:_Nutrition_and_the_Human_Body/2.2:_The_Basic_Structural_and_Functional_Unit_of_Life:_The_Cell |archive-date=29 March 2020 |access-date=29 March 2020 |publisher=LibreTexts}}</ref><ref>{{cite web |last=Bose |first=Debopriya |date=14 May 2019 |title=Six Main Cell Functions |url=https://sciencing.com/six-main-cell-functions-6891800.html |url-status=live |archive-url=https://web.archive.org/web/20200329060221/https://sciencing.com/six-main-cell-functions-6891800.html |archive-date=29 March 2020 |access-date=29 March 2020 |publisher=Leaf Group Ltd./Leaf Group Media}}</ref> [[Cell theory]] was formulated by [[Henri Dutrochet]], [[Theodor Schwann]], [[Rudolf Virchow]] and others during the early nineteenth century, and subsequently became widely accepted.<ref name=sapp2003>{{cite book |first1=Jan |last1=Sapp |title=Genesis: The Evolution of Biology |publisher=Oxford University Press |date=2003 |isbn=978-0-19-515619-5 |pages=[https://archive.org/details/genesisevolution00sapp/page/75 75]–78 |url=https://archive.org/details/genesisevolution00sapp |url-access=registration }}</ref> The activity of an organism depends on the total activity of its cells, with [[Cellular respiration|energy flow]] occurring within and between them. Cells contain hereditary information that is carried forward as a [[genetics|genetic]] code during cell division.<ref>{{cite journal |last1=Lintilhac |first1=P.M. |title=Thinking of biology: toward a theory of cellularity—speculations on the nature of the living cell |journal=BioScience |date=Jan 1999 |volume=49 |issue=1 |pages=59–68 |pmid=11543344 |url=https://www.rz.uni-karlsruhe.de/~db45/Studiendekanat/Lehre/Master/Module/Botanik_1/M1401/Evolution_Zellbiologie/Lintilhac%202003.pdf |access-date=2 June 2012 |doi=10.2307/1313494 |jstor=1313494 |url-status=dead |archive-url=https://web.archive.org/web/20130406043511/https://www.rz.uni-karlsruhe.de/~db45/Studiendekanat/Lehre/Master/Module/Botanik_1/M1401/Evolution_Zellbiologie/Lintilhac%202003.pdf |archive-date=6 April 2013}}</ref> There are two primary types of cells, reflecting their evolutionary origins. [[Prokaryote]] cells lack a [[Cell nucleus|nucleus]] and other membrane-bound [[organelle]]s, although they have circular DNA and [[ribosome]]s. Bacteria and [[Archaea]] are two [[domain (biology)|domains]] of prokaryotes. The other primary type is the [[eukaryote]] cell, which has a distinct nucleus bound by a nuclear membrane and membrane-bound organelles, including [[mitochondria]], [[chloroplasts]], [[lysosomes]], rough and smooth [[endoplasmic reticulum]], and [[vacuoles]]. In addition, their DNA is organised into [[chromosome]]s. All species of large complex organisms are eukaryotes, including animals, plants and fungi, though with a wide diversity of [[protist]] [[microorganism]]s.<ref>{{Cite journal |last1=Whitman |first1=W. |last2=Coleman |first2=D. |last3=Wiebe |first3=W. |title=Prokaryotes: The unseen majority |doi=10.1073/pnas.95.12.6578 |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=95 |issue=12 |pages=6578–6583 |year=1998 |pmid=9618454 |pmc=33863 |bibcode=1998PNAS...95.6578W|doi-access=free }}</ref> The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through [[endosymbiosis]] between bacteria and the progenitor eukaryotic cell.<ref>{{cite journal |first1=Norman R. |last1=Pace |title=Concept Time for a change |journal=Nature |volume=441 |page=289 |date=18 May 2006 |doi=10.1038/441289a |url=http://coursesite.uhcl.edu/NAS/Kang/BIOL3231/Week3-Pace_2006.pdf |archive-url=https://web.archive.org/web/20121016220349/http://coursesite.uhcl.edu/NAS/Kang/BIOL3231/Week3-Pace_2006.pdf |archive-date=16 October 2012 |url-status=dead |access-date=2 June 2012 |pmid=16710401 |bibcode=2006Natur.441..289P |issue=7091|s2cid=4431143 }}</ref> The molecular mechanisms of [[cell biology]] are based on [[protein]]s. Most of these are synthesised by the ribosomes through an [[Enzyme catalysis|enzyme-catalyzed]] process called [[protein biosynthesis]]. A sequence of amino acids is assembled and joined based upon [[gene expression]] of the cell's nucleic acid.<ref>{{cite web |title=Scientific background |website=The Nobel Prize in Chemistry 2009 |publisher=Royal Swedish Academy of Sciences |url=https://www.nobelprize.org/nobel_prizes/chemistry/laureates/2009/advanced.html |access-date=10 June 2012 |url-status=live |archive-url=https://web.archive.org/web/20120402150754/http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2009/advanced.html |archive-date=2 April 2012 }}</ref> In eukaryotic cells, these proteins may then be transported and processed through the [[Golgi apparatus]] in preparation for dispatch to their destination.<ref name="pmid20605430">{{cite journal|last1=Nakano |first1=A. |last2=Luini |first2=A. |year=2010 |title=Passage through the Golgi |journal=Current Opinion in Cell Biology |volume=22 |issue=4 |pages=471–478 |doi=10.1016/j.ceb.2010.05.003 |pmid=20605430 }}</ref> Cells reproduce through a process of [[cell division]] in which the parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of [[Fission (biology)|fission]] in which the DNA is replicated, then the two copies are attached to parts of the cell membrane. In [[eukaryote]]s, a more complex process of [[mitosis]] is followed. However, the result is the same; the resulting cell copies are identical to each other and to the original cell (except for [[mutations]]), and both are capable of further division following an [[interphase]] period.<ref>{{cite book |first1=Joseph |last1=Panno |title=The Cell |series=Facts on File science library |publisher=Infobase Publishing |date=2004 |isbn=978-0-8160-6736-7 |pages=60–70 |url=https://books.google.com/books?id=sYgKY6zz20YC&pg=PA60 |access-date=10 August 2023 |archive-date=13 April 2023 |archive-url=https://web.archive.org/web/20230413194758/https://books.google.com/books?id=sYgKY6zz20YC&pg=PA60 |url-status=live }}</ref> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here. 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