Question

Which of these is a non-symbiotic nitrogen fixer?
(a)Azotobacter
(b)Pseudomonas
(c)Soil Fungi
(d)Blue-green algae

Answer 1

Nitrogen-fixing is an important process as we can not use the nitrogen present in the atmosphere directly, this process helps us to attain that. This process is mainly done by soil microorganisms in free-living and symbiotic forms.

Complete answer:
Azotobacter is not a symbiotic nitrogen fixer. These are free-living nitrogen fixers along with cyanobacteria, clostridium, etc. Azotobacter genus contains diazotrophic bacteria found mainly in neutral to alkaline soils, especially in aquatic environments and on some plants. It fixes nitrogen to convert it to ammonia.

Additional Information: Nitrogen fixation is the process of conversion of nitrogen molecules in the atmosphere to ammonia or related nitrogenous compounds. Except for lightning and ultraviolet rays, the natural fixation occurs mainly by soil microorganisms. They can be either free-living or symbiotic. Free-living ones are cyanobacteria, Azotobacter, Clostridium, Anabaena, etc. Examples of symbiotic nitrogen fixers are Rhizobium.
Here's some information about the mentioned organisms:
-Pseudomonas: It is a genus of gram-negative bacterias that causes infections in the body under certain circumstances. They live and breed in water, soil, and damp areas. They can perform the process of denitrification i.e. the reduction of nitrates back into nitrogen gas.
-Soil fungi: These are plant-like cells that grow to form a mycelium. It absorbs nutrients from the roots where it has colonized or the soil. They decompose the lignin and hard-to-digest organic matter in the soil. They are able to use nitrogen from the soil to decompose surface residues which are low in nitrogen.
-Blue-green algae: This phylum consists of both free-living bacteria and the endosymbiotic plastids present in the Archaeplastida autotrophic eukaryotes. While fixing carbon from carbon dioxide, certain blue-green algae may fix nitrogen from the atmosphere as well, including symbiotic and free-living forms.
So, the correct answer is ‘Azotobacter’.

Note: Members of both Azotobacter genus and phylum cyanobacteria are capable of Nitrogen fixation and live freely without forming a symbiotic bond with other organisms. However, some members of phylum cyanobacteria are symbiotic too. So in this case, Azotobacter should be considered as the right answer.