Question

How is nitrogen fixation important to animals?

Answer 1

The conversion of inert gaseous molecular Dinitrogen into salts of Nitrogen that can be assimilated by plants is called nitrogen fixation. Nitrogen fixation is of two types, abiological and biological. Abiological nitrogen fixation is of two types, natural and industrial.
1. Natural or Atmospheric Nitrogen Fixation. It constitutes about 10% of the total nitrogen fixation. Lightning dissociates water vapors and oxygen into highly reactive free hydroxyl radicals, hydrogen atoms and oxygen atoms. They combine with Dinitrogen to produce nitric acid.
2. Industrial Nitrogen Fixation. It produces nitrogen fertilizers. Roughly 30% of nitrogen fixation or about 80 million tons of fertilizers are produced industrially. It is done through the Haber-Bosch process. Dinitrogen and hydrogen are made to combine at a temperature of 300-400°C and pressure of 35-100 MPa.

Complete answer:
It constitutes 60% of total nitrogen fixation and is very important in natural ecosystems as well as in agriculture. There are two groups of microorganisms that perform nitrogen fixation, bacteria and blue-green algae (cyanobacteria). Nitrogen fixers are of further two types, free living and symbiotic.
1. Free Living Nitrogen Fixing Bacteria: Azotobacter , Beijerinckia , Azospirillum , Derxia, Clostridium , Methanococcus , Bacillus , Klebsiella , Desulfovibrio , Chromatium.
2. Free living nitrogen fixing blue green algae: Anabaena , Nostoc , Aulosira , Calothrix , Cylindrospermum , Oscillatoria , Phormidium , Gloeocapsa.
3. Symbiotic Nitrogen fixing Blue green algae: Nostoc and Anabaena are the two common blue green algae which occur as symbionts in Gunnera , coralloid roots of Cycas , fronds of Azolla pinnata , Anthoceros and many lichens. Azolla pinnata is commonly allowed to grow in paddy fields to provide extra nitrogen. Its fronds contain blue-green algae Anabaena azollae.
4. Symbiotic Nitrogen Fixing Bacteria: The most common nitrogen fixing bacteria are rhizobia. They occur in legume root nodules. Recently they have been split up to form a number of genera like Azorhizobium (in Sesbania), Bradyrhizobium japonicum , Sinorhizobium fredii (both in Soybean or Glycine max), Sinorhizobium meliloti (in Alfalfa or Medicago sativa), Photo Rhizobium (in Aeschynomene) and Rhizobium leguminosarum (e.g., in Pea, Clover, Bean, Lentil, Chick Pea) with a number of varieties. They form root nodules. The only nonlegume having Rhizobium type bacteria in its root nodules is Paraspania (= Trema, family Ulmaceae). The bacteria belong to Bradyrhizobium.
Frankia is symbiont in the most nodules of a number of non leguminous plants like Alnus (Alder), Casuarina , Myrica. It is an actinomycetes or filamentous bacterium. Some bacterial symbionts occur in cavities inside leaves of Ardisia and several members of family rubiaceae. They belong to genera Xanthomonas and Mycobacterium.
Nitrogen fixing is vital to life as fixed inorganic nitrogen compounds are essential to biosynthesize nitrogen containing compounds, like nucleic acids, Proteins.
Nitrogen fixation is an important process as nitrogen cannot be used directly.It has to be converted to absorbable form. Fixed Nitrogen is then used by plants. Animals in turn derive their nitrogen requirements from plants. In this way, nitrogen fixation is important to animals. Hence, it is important to fix nitrogen to carry out life processes.

Note:
Legume-Rhizobium association can annually fix 25-60 kg of nitrogen per hectare. Non-symbiotic bacteria fix only upto 5-20 kg of nitrogen per hectare in one year. Rhizobia and Frankia are unable to perform nitrogen fixation when they occur free in the soil. The faculty develops only in association with a suitable host. The bacterial symbionts, being microscopic, are also called micro symbionts.