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Which of the following organisms fix nitrogen in aquatic ecosystems?

1. Fungi
2. Chemoautotrophs
3. Cyanobacterial
4. Phytoplankton

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Correct Answer - Option 3 : Cyanobacterial

The correct answer is Cyanobacterial​.


  • Cyanobacteria have a unique ecological role in aquatic ecosystems, as they are the only group of organisms on Earth that can fix both inorganic carbon and nitrogen in an anoxic (oxygen-containing) environment.


  • Nitrification is the process in which the ammonia is converted into Nitrate.
  • Nitrification is a two-step process and based upon these two steps, the bacteria are divided into Nitrosifying and Nitrite-Oxidizing bacteria.
  • An example of Nitrosifying bacteria is Nitrosomonas, which converts ammonia (NH3) into Nitrite (NO2-).
  • An example of Nitrite-Oxidizing bacteria is Nitrobacter which is able to oxidize the Nitrite and crate Nitrate (NO3-).

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