Editing Biochemistry (section)

== Starting materials: the chemical elements of life ==
[[Image:201 Elements of the Human Body.02.svg|thumb|upright|The main elements that compose the human body shown from most abundant (by mass) to least abundant]]
{{main|Composition of the human body|Dietary mineral}}

Around two dozen [[chemical elements]] are essential to various kinds of [[life|biological life]]. Most rare elements on Earth are not needed by life (exceptions being  [[selenium]] and [[iodine]]),<ref>{{cite book |last1=Cox, Nelson, Lehninger |title=Lehninger Principles of Biochemistry |date=2008 |publisher=Macmillan}}</ref> while a few common ones ([[aluminium]] and [[titanium]]) are not used. Most organisms share element needs, but there are a few differences between [[plants]] and [[animals]]. For example, ocean algae use [[bromine]], but land plants and animals do not seem to need any. All animals require [[sodium]], but is not an essential element for plants. Plants need [[boron]] and [[silicon]], but animals may not (or may need ultra-small amounts).<ref>{{Cite journal |last1=Sheng |first1=Huachun |last2=Lei |first2=Yuyan |last3=Wei |first3=Jing |last4=Yang |first4=Zhengming |last5=Peng |first5=Lianxin |last6=Li |first6=Wenbing |last7=Liu |first7=Yuan |date=2024 |title=Analogy of silicon and boron in plant nutrition |journal=Frontiers in Plant Science |volume=15 |pages=1353706 |doi=10.3389/fpls.2024.1353706 |doi-access=free |issn=1664-462X |pmc=10877001 |pmid=38379945|bibcode=2024FrPS...1553706S }}</ref>

Just six elements—[[carbon]], [[hydrogen]], [[nitrogen]], [[oxygen]], [[calcium]] and [[phosphorus]]—make up almost 99% of the mass of living cells, including those in the human body (see [[composition of the human body]] for a complete list). In addition to the six major elements that compose most of the human body, humans require smaller amounts of possibly 18 more.<ref>[[#Nielsen|Nielsen]] (1999), pp. 283–303.</ref>