Editing Photosynthesis (section)

====In water====
[[Cyanobacteria]] possess [[carboxysome]]s, which increase the concentration of {{co2}} around RuBisCO to increase the rate of photosynthesis. An enzyme, [[carbonic anhydrase]], located within the carboxysome, releases CO<sub>2</sub> from dissolved [[Hydrocarbonate|hydrocarbonate ions]] (HCO{{su|b=3|p=−}}). Before the CO<sub>2</sub> can diffuse out<!-- of what? -->, RuBisCO concentrated within the carboxysome quickly sponges it up. HCO{{su|b=3|p=−}} ions are made from CO<sub>2</sub> outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO<sub>2</sub> very slowly without the help of carbonic anhydrase. This causes the HCO{{su|b=3|p=−}} ions to accumulate within the cell from where they diffuse into the carboxysomes.<ref>{{cite journal |vauthors= Badger MR, Price GD |date= February 2003 |title= CO2 concentrating mechanisms in cyanobacteria: molecular components, their diversity and evolution |journal= [[Journal of Experimental Botany]] |volume= 54 |issue= 383 |pages= 609–622 |doi= 10.1093/jxb/erg076 |doi-access= free |pmid= 12554704 }}</ref> [[Pyrenoid]]s in [[algae]] and [[hornwort]]s also act to concentrate {{co2}} around RuBisCO.<ref>{{Cite journal |vauthors=Badger MR, Andrews JT, Whitney SM, Ludwig M, Yellowlees DC, Leggat W, Price GD |year= 1998 |title= The diversity and coevolution of Rubisco, plastids, pyrenoids, and chloroplast-based CO<sub>2</sub>-concentrating mechanisms in algae |journal= [[Canadian Journal of Botany]] |volume= 76 |issue= 6 |pages= 1052–1071 |doi= 10.1139/b98-074 |bibcode= 1998CaJB...76.1052B }}</ref><ref>{{cite journal | vauthors=((Robison, T. A.)), ((Oh, Z. G.)), ((Lafferty, D.)), ((Xu, X.)), ((Villarreal, J. C. A.)), ((Gunn, L. H.)), ((Li, F.-W.)) | journal=Nature Plants | title=Hornworts reveal a spatial model for pyrenoid-based CO2-concentrating mechanisms in land plants | pages=63–73 | publisher=Nature Publishing Group | date=3 January 2025 | volume=11 | issue=1 | issn=2055-0278 | doi=10.1038/s41477-024-01871-0| pmid=39753956 }}
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