Aquatic Organisms and Chemical Transitions in the Hydrosphere

Aquatic organisms, especially single-celled microorganisms, are very much involved in chemical transitions in the hydrosphere. Most of them are oxidation-reduction reactions (see Section 3.7). 

Two very important microbial transitions involve carbon. The first of these is photosynthesis, which is powered by solar energy from the sun (represented by light photon energy, hv, in which h is Planck s constant and v is the frequency of light radiation), in which carbon dioxide, largely from the atmosphere, is converted to biomass, represented by the general formula CH2O  

A second important microbially mediated reaction is the opposite of photosynthesis in which biomass is oxidized biochemically by elemental oxygen, converting the carbon in biomass to carbon dioxide  

The same process acts in the biodegradation of pollutant chemicals in the hydrosphere. 

Several important microbially mediated elemental transitions in the hydrosphere involve nitrogen. Nitrogen fixation is the process in which elemental nitrogen from the atmosphere is converted to organic or ammoniacal nitrogen  

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