Biology · Environmental Studies

Microbiology and Nitrogen Cycle

1,029 Questions

This hub focuses on microbiology and the nitrogen cycle, covering essential concepts about bacteria and soil microbes. Topics include nitrogen fixation, bacterial structures, and soil microbial processes. These concepts are frequently tested in general science sections of various competitive exams.

Nitrogen fixing bacteriaGram-positive bacteriaBacterial flagellaDenitrifying bacteriaAmmonia conversion processBacterial resting spores

Microbiology and Nitrogen Cycle Questions

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Which one of the following microorganisms forms a symbiotic association with plants and helps them in their nutrition?

  1. Glomus

  2. Azotobacter

  3. Klebsielfa

  4. Azospirillium
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Several fungi are known to form symbiotic associations with plants, i.e., mycorrhiza. The most common fungal partners of mycorrhiza are Glomus species.

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Study the following statements and select the correct ones.


(i) Methanogens are archaebacteria that produce methane in marshy areas.
(ii) Nostoc is a filamentous blue-green alga which fixes atmospheric nitrogen.
(iii) Many members of the genus Glomus form mycorrhiza.

  1. (i) and (ii)

  2. (i) and (iii)

  3. (ii) and (iii)

  4. (i), (ii) and (iii)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
1. Methanogens are archaebacteria belong to the domain of archaea, commonly found in wet, marshy areas,  They produce methane gas.
2. Nostoc is the filamentous blue-green alga. They form gelatin body which contains trichomes.
3. Glomus and it's all species form symbiotic relationships (mycorrhizas) with plant roots. 
So the correct answer is option D.

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Which one of the following can fix nitrogen?

  1. Vaucheria

  2. Spirogyra

  3. Nostoc

  4. Ectocarpus
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The atmospheric nitrogen is not available to plants. There are some nitrogen-fixing bacteria which converts atmospheric nitrogen into ammonia which is readily available to plants. Nostoc is a cyanobacterium. It has the ability to fix atmospheric nitrogen. The heterocysts present in it contains nitrogenase enzyme. These are specialized for nitrogen fixation. 
Thus, the correct answer is 'Nostoc.'
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Some blue green algae are used as biofertilizers because they

  1. Are photosynthetic

  2. Have mucilage

  3. Grow everywhere

  4. Fix nitrogen
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The atmospheric nitrogen is not available to plants. There are some nitrogen fixing bacteria which converts atmospheric nitrogen into ammonia which is readily available to plants. Some blue green algae like Anabaena and Nostoc have the ability to fix the atmospheric nitrogen. They are free-living nitrogen fixing bacteria. Hence, they are used as biofertilizers in the field of rice. 
Thus, the correct answer is 'Fix nitrogen.'
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Aquatic fern which is an excellent biofertilizer is

  1. <p>Salvinia</p>

  2. <p>Azolla</p>

  3. <p>Marsilea</p>

  4. <p>Pteridium</p>
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Biofertilizers are organisms that enrich the nutrient quality of the soil. The main source of biofertilizers are bacteria, fungus, and cyanobacteria. Symbiotic cyanobacteria Anabaena azollae fixes nitrogen in the leaves of Azolla ( aquatic fern ). Azolla pinnata ( a pteridophyte ) is used as an excellent biofertilizer in the rice field. 

So, the correct answer is 'Azolla'

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Most active nitrogen fixing blue-green algae of rice fields is

  1. <p>Anabaena azollae</p>

  2. <p>Aulosira fertilissima</p>

  3. <p>Cylindrospermum licheniforme</p>

  4. <p>Nostoc cycadacearum</p>
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen. In paddy fields, cyanobacteria serve as an important biofertilizer. 

Aulosira fertilissima is the most active non-symbiotic nitrogen fixer in rice field in India. Hence, Option B is correct.

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Some blue green algae can be used as biofertilizer as they are

  1. Photosynthesis

  2. Surrounded by mucilage

  3. Growing every where

  4. Capable of fixing nitrogen
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Some cyanobacteria can fix atmospheric nitrogen in anaerobic conditions by means of specialized cells called heterocysts. These heterocyst forming species are specialized for nitrogen fixation, and are able to fix nitrogen gas into ammonia, nitrites, or nitrates, which can be absorbed by plants and converted to proteins and nucleic acids as nitrogen cannot be directly absorbed by plants. Therefore, some of the cyanobacterial species are used as biofertilizers. 

So, the correct answer is 'Capable of fixing nitrogen'

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Cyanobacteria are / Nostoc is

  1. Oxygenic with nitrogenase

  2. Oxygenic without nitrogenase

  3. Non- Oxygenic with nitrogenase

  4. Non - Oxygenic without nitrogenase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The cyanobacteria fix atmospheric nitrogen through the help of enzyme nitrogenase and are oxygenic photosynthetic also.

So, the correct option is 'Oxygenic with nitrogenase'.