Editing Chlorophyll (section)

==Photosynthesis==
[[File:Chlorophyll ab spectra-en.svg|thumb|right|[[Absorbance]] spectra of free chlorophyll&nbsp;''a'' ('''<span style="color:#0169c9;">blue</span>''') and ''b'' ('''<span style="color:red;">red</span>''') in a solvent. The spectra of chlorophyll molecules are slightly modified ''in vivo'' depending on specific pigment-protein interactions.
{{legend|#0169C9|Chlorophyll&nbsp;''a''}}
{{legend|red|Chlorophyll&nbsp;''b''}}]]
Chlorophyll is vital for [[photosynthesis]], which allows plants to absorb energy from [[light]].<ref>{{cite web | vauthors = Carter JS | year =1996 | title =Photosynthesis | publisher =[[University of Cincinnati]] | url =http://biology.clc.uc.edu/courses/bio104/photosyn.htm | url-status =dead | archive-url = https://web.archive.org/web/20130629204107/http://biology.clc.uc.edu/courses/bio104/photosyn.htm | archive-date =2013-06-29 }}</ref>

Chlorophyll molecules are arranged in and around [[photosystem]]s that are embedded in the [[thylakoid]] membranes of [[chloroplast]]s.<ref>{{Cite web |title=Photosynthesis, Chloroplast {{!}} Learn Science at Scitable |url=https://www.nature.com/scitable/topicpage/photosynthetic-cells-14025371/ |access-date=2024-10-19 |website=www.nature.com |language=en}}</ref> In these complexes, chlorophyll serves three functions:
# The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light.
# Having done so, these same centers execute their second function: The transfer of that energy by [[resonance energy transfer]] to a specific chlorophyll pair in the [[reaction center]] of the photosystems.
# This specific pair performs the final function of chlorophylls: Charge separation, which produces the unbound protons (H{{sup|+}}) and electrons (e{{sup|−}}) that separately propel biosynthesis.

The two currently accepted photosystem units are {{nobr|[[photosystem I]]}} and {{nobr|[[photosystem II]],}} which have their own distinct reaction centres, named [[P700]] and [[P680]], respectively. These centres are named after the wavelength (in [[nanometer]]s) of their red-peak absorption maximum. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by each other and the protein structure surrounding them.

The function of the reaction center of chlorophyll is to absorb light energy and transfer it to other parts of the photosystem. The absorbed energy of the photon is transferred to an electron in a process called charge separation. The removal of the electron from the chlorophyll is an oxidation reaction. The chlorophyll donates the high energy electron to a series of molecular intermediates called an [[electron transport chain]]. The charged reaction center of chlorophyll (P680<sup>+</sup>) is then reduced back to its ground state by accepting an electron stripped from water. The electron that reduces P680<sup>+</sup> ultimately comes from the oxidation of water into O<sub>2</sub> and H<sup>+</sup> through several intermediates. This reaction is how photosynthetic organisms such as plants produce O<sub>2</sub> gas, and is the source for practically all the O<sub>2</sub> in Earth's atmosphere. Photosystem&nbsp;I typically works in series with Photosystem&nbsp;II; thus the P700<sup>+</sup> of Photosystem&nbsp;I is usually reduced as it accepts the electron, via many intermediates in the thylakoid membrane, by electrons coming, ultimately, from Photosystem&nbsp;II. Electron transfer reactions in the thylakoid membranes are complex, however, and the source of electrons used to reduce P700<sup>+</sup> can vary.

The electron flow produced by the reaction center chlorophyll pigments is used to pump H<sup>+</sup> ions across the thylakoid membrane, setting up a [[proton-motive force]] a chemiosmotic potential used mainly in the production of [[Adenosine triphosphate|ATP]] (stored chemical energy) or to reduce NADP<sup>+</sup> to [[NADPH]]. NADPH is a universal [[redox|agent]] used to reduce CO<sub>2</sub> into sugars as well as other biosynthetic reactions.

Reaction center chlorophyll–protein complexes are capable of directly absorbing light and performing charge separation events without the assistance of other chlorophyll pigments, but the probability of that happening under a given light intensity is small. Thus, the other chlorophylls in the photosystem and antenna pigment proteins all cooperatively absorb and funnel light energy to the reaction center. Besides chlorophyll&nbsp;''a'', there are other pigments, called [[accessory pigment]]s, which occur in these pigment–protein antenna complexes.