What enables leguminous plants to fix nitrogen
Junior High


  • Excellent question! Nitrogen is fairly inert, you have to really push it to combine, like sparking it with oxygen - a process discovered by the great Henry Cavendish in the late 18thC. Nitric acid is the end result:
  • N2 + 02 = 2 NO. NO + O = NO2. NO2 (nitrogen dioxide, a brown poisonous gas, don’t breathe it!, or in a cold winter, a yellow liquid) with water gives nitric acid (HNO3).
  • Leguminous plants do it with the aid of micro-organisms which are in the roots. they produce organic nitrogen compounds - these are the ones animals eat. When they die ammonia (NH3) is produced, this is oxidized into nitrites (NO2 -) by more bacteria & on to nitrates (NO3 -). the fundamental salts for plants.
  • Industially, If we produce N for our plants we start with ammonia (produced by sparking H2 & N2) and make various ammonium salts.
  • Symbiotic bacteria like rhizobium which lives with the roots of leguminous plants enables them to fix atmospheric nitrogen by making root nodules. These root nodules are strong association of bacteria and roots of plants.
  • It has leg haemoglobin which eats free oxygen in the nodules creating inert atmosphere for nitrogenase enzyme. Nitrogenase enzyme fixes nitrogen gas in nitrates at the expense of ATP molecules.


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