Question

Nitrogen fixation is performed by
A)Green algae and fungi
B)Ferns and cycads
C)Legumes and cereals
D)Blue-green algae and bacteria

Answer 1

Nitrogen is an important component of biomolecules such as nucleic acids and proteins. Atmospheric nitrogen cannot be utilized by plants and other living organisms. The conversion of non-usable nitrogen into usable nitrogen forms such as ammonia is known as nitrogen fixation.

Complete answer:
Non-usable forms of nitrogen are converted to usable forms by blue-green algae and some bacteria.
Nitrogen can be fixed by the following methods :
Physical nitrogen fixation: Dinitrogen reacts with oxygen to form nitric oxide in the process of lightning. nitric oxide form nitrous and nitric acid and mix with rain causing acid rain which then mixes with soil.

Biological nitrogen fixation: Biological nitrogen fixers such as Azotobacter, Rhizobium, Anabaena utilize molecular nitrogen from the atmosphere and are converted to ammonia in the presence of nitrogenous catalysts.
Rhizobium and leguminous plants have a symbiotic relationship with each other. Rhizobium bacteria live in the roots of leguminous plants and convert non-usable nitrogen in a usable form. Usable forms of nitrogen dissolve in the soil and are used by leguminous plants.

Hence option D) Nitrogen fixation is performed by blue-green algae and bacteria.
Nitrification is oxidation of ammonia to nitrite and nitrite oxidation to nitrate and denitrification in the process of conversion of nitrite and nitrate into atmospheric nitrogen. Formation of organic nitrogen compounds from inorganic-organic compounds is known as nitrogen assimilation.

Hence, the correct answer is option (D)

Note: Nitrogen fixation is the process by which non-usable atmospheric nitrogen is converted into a usable form. Nitrogen is fixed by the physical method by lightning and biologically by biological nitrogen fixers such as blue-green algae and bacteria e.g. Azotobacter, Rhizobium, Anabaena. Nitrogen is converted to ammonia which is utilised by plants.