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| Answer» <html><body><p><strong>Answer:</strong></p><p></p><p><strong>Explanation:</strong></p><ul><li> Nitrogen <a href="https://interviewquestions.tuteehub.com/tag/exists-979838" style="font-weight:bold;" target="_blank" title="Click to know more about EXISTS">EXISTS</a> 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.</li><li>In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO₂, N₂O).</li><li> Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides. </li><li>Decomposition of organic nitrogen of dead plants and <a href="https://interviewquestions.tuteehub.com/tag/animals-875924" style="font-weight:bold;" target="_blank" title="Click to know more about ANIMALS">ANIMALS</a> into ammonia is called ammonification. </li><li>Some of this ammonia volatilises and re-enters the atmosphere but most of it is converted into nitrate by soil bacteria.</li><li>Ammonia is first oxidised to nitrite by the bacteria Nitrosomonas and/or Nitrococcus. </li><li>The nitrite is further oxidised to nitrate with the help of the bacterium Nitrobacter. These steps are called nitrification. These nitrifying bacteria are chemoautotrophs.</li><li>The nitrate thus formed is absorbed by plants and is transported to the leaves. </li><li>In leaves, it is reduced to form ammonia that finally forms the amine group of amino acids.</li><li> Nitrate present in the soil is also reduced to nitrogen by the process of denitrification. Denitrification is carried by bacteria Pseudomonas and Thiobacillus.</li></ul><p> 2NH₃ + 3O₂ ⇒ 2NO₂⁻ + 2H⁺ + 2H₂O</p><p>2NO₂⁻ + O₂ ⇒2NO₃⁻</p><p><strong>AMMONIFICATION</strong></p><p> N ≡ N ⇒ NH₃ by nitrogenase</p><p>N₂ + 8e⁻ + 8H⁺ +16ATP ⇒ 2NH₃ + H₂ + 16ADP + 16Pi</p><ul><li>Nodule formation involves a sequence of <a href="https://interviewquestions.tuteehub.com/tag/multiple-1105557" style="font-weight:bold;" target="_blank" title="Click to know more about MULTIPLE">MULTIPLE</a> interactions between Rhizobium and roots of the host plant.</li><li>The nodule contains all the necessary biochemical components, such as the enzyme nitrogenase and leghaemoglobin. </li><li>The enzyme nitrogenase is a Mo-Fe protein and catalyses the conversion of atmospheric nitrogen to ammonia.</li><li>The enzyme nitrogenase is highly sensitive to the molecular oxygen; it requires anaerobic conditions. </li><li>The nodules have adaptations that ensure that the enzyme is protected from oxygen. </li><li>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). </li><li>You must have <a href="https://interviewquestions.tuteehub.com/tag/noticed-2877256" style="font-weight:bold;" target="_blank" title="Click to know more about NOTICED">NOTICED</a> in the above reaction that the ammonia synthesis by nitrogenease requires a very <a href="https://interviewquestions.tuteehub.com/tag/high-479925" style="font-weight:bold;" target="_blank" title="Click to know more about HIGH">HIGH</a> input of energy (8 ATP for each NH3 produced). The energy required, thus, is obtained from the respiration of the host cells.</li></ul><p></p></body></html> | |