Question

The process of nitrogen-fixation by bacteria does not takes place in the presence of:
A.Molecular form of Hydrogen.
B.Elemental form of Oxygen
C.Water
D.Elemental form of nitrogen

Answer 1

The bacteria of species Rhizobium is associated with the nitrogen fixation bacteria. These are anaerobic bacteria which work in the absence of oxygen for the process of nitrogen fixation.

Complete answer:
Nitrogen fixation is an essential life process because it fixes inorganic nitrogen compounds that are required for the biosynthesis of all nitrogen-containing organic compounds, such as amino acids and proteins, nucleoside triphosphates and nucleic acids. Nitrogen fixation is a process in which the conversion of atmospheric nitrogen into ammonia and organic derivatives takes place by natural means. Nitrogen fixation takes elemental nitrogen and converts it into an ammonia; a form which is used by biological organisms. Nitrogen fixation is carried out naturally in soil by microorganism diazotrophs such as Azotobacter and archaea. They form a symbiotic relationship with the root nodules of the leguminous plants.
The nitrogenase enzyme in this bacterium helps in the fixation of the atmospheric nitrogen to nitrates which can be used for the growth of the plants. This enzyme is activated in the absence of oxygen and nitrogen fixation takes place. The obligate anaerobic bacteria participate in the process of nitrogen fixation. These nitrogenase enzymes are very crucial and get easily destroyed in presence of oxygen. Many bacteria cease the production of enzymes in the presence of oxygen. Many nitrogen fixing bacteria grow in anaerobic conditions or respire to bring down oxygen levels or binding oxygen with the proteins like leg hemoglobin.

Hence, the correct answer is option (B)

Note: Certain bacteria such as Azotobacter and Rhizobium, convert the atmospheric nitrogen into water soluble nitrates. The process of biofixation of nitrogen is called nitrogen fixation which takes place in presence of enzyme nitrogenase which is susceptible to destruction in presence of oxygen.