Dioxygen is uised in cellular respiration an mony major classes o organic molecules in livin organisms conteen oxygen, sic as proteins, nucleic acids, carbohydrates, an fats, as dae the major consteetuent inorganic compoonds o ainimal shells, teeth, an bane. Maist o the mass o livin organisms is oxygen as a component o watter, the major constituent o lifeforms. Conversely, oxygen is continuously replenished bi photosynthesis, which uises the energy o sunlicht tae produce oxygen frae watter an carbon dioxide. Oxygen is ower chemically reactive tae remeen a free element in air withoot bein continuously replenished bi the photosynthetic action o livin organisms. Anither form (allotrope) o oxygen, ozone (O 3), strangly absorbs ultraviolet UVB radiation an the heich-altitude ozone layer helps pertect the biosphere frae ultraviolet radiation. But ozone is a pollutant near the surface whaur it is a bi-product o smog. At law yird orbit altitudes, sufficient atomic oxygen is present tae cause corrosion o spacecraft.[7]
Oxygen wis discovered independently bi Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, an Joseph Priestley in Wiltshire, in 1774, but Priestley is eften gien priority acause his wark wis published first. The name oxygen wis coined in 1777 bi Antoine Lavoisier,[8] whase experiments wi oxygen helped tae discredit the then-popular phlogiston theory o combustion an corrosion. Its name derives frae the Greek roots ὀξύς oxys, "acid", leeterally "sharp", referrin tae the soor taste o acids an -γενής -genes, "producer", leeterally "begetter", acause at the time o namin, it wis mistakenly thocht that aw acids required oxygen in thair composeetion.
