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Answer 1

Answer:

Explanation:

• Nitrogen exists as two nitrogen atoms joined by a very strong triple covalent bond (N ≡ N). The process of conversion of nitrogen (N₂) to ammonia is termed as nitrogen-fixation.
• In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO₂, N₂O).
• Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.
• Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
• Some of this ammonia volatilises and re-enters the atmosphere but most of it is converted into nitrate by soil bacteria.
• Ammonia is first oxidised to nitrite by the bacteria Nitrosomonas and/or Nitrococcus.
• The nitrite is further oxidised to nitrate with the help of the bacterium Nitrobacter. These steps are called nitrification. These nitrifying bacteria are chemoautotrophs.
• The nitrate thus formed is absorbed by plants and is transported to the leaves.
• In leaves, it is reduced to form ammonia that finally forms the amine group of amino acids.
• Nitrate present in the soil is also reduced to nitrogen by the process of denitrification. Denitrification is carried by bacteria Pseudomonas and Thiobacillus.

2NH₃ + 3O₂ ⇒ 2NO₂⁻ + 2H⁺ + 2H₂O

2NO₂⁻ + O₂  ⇒2NO₃⁻

AMMONIFICATION

    N ≡ N ⇒ NH₃ by nitrogenase

N₂ + 8e⁻ + 8H⁺ +16ATP ⇒ 2NH₃ + H₂ + 16ADP + 16Pi

• Nodule formation involves a sequence of multiple interactions between Rhizobium and roots of the host plant.
• The nodule contains all the necessary biochemical components, such as the enzyme nitrogenase and leghaemoglobin.
• The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen to ammonia.
• The enzyme nitrogenase is highly sensitive to the molecular oxygen; it requires anaerobic conditions.
• The nodules have adaptations that ensure that the enzyme is protected from oxygen.
• To protect these enzymes, the nodule contains an oxygen scavenger called leg-haemoglobin. It is interesting to note that these microbes live as aerobes under free-living conditions (where nitrogenase is not operational), but during nitrogen-fixing events, they become anaerobic (thus protecting the nitrogenase enzyme).
• You must have noticed in the above reaction that the ammonia synthesis by nitrogenease requires a very high input of energy (8 ATP for each NH3­ produced). The energy required, thus, is obtained from the respiration of the host cells.

Answer 2

Nitrogen fixation is the chemical processes by which atmospheric nitrogen is assimilated into organic compounds, especially by certain microorganisms as part of the nitrogen cycle.

Ways in which nitrogen can be fixed are:-

first, by lightning; second, by industrial methods; finally, by bacteria living in the soil.

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