Biology · Environmental Studies

Microbiology and Nitrogen Cycle

950 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

Multiple choice zoology microbes in human welfare biofertilizers microbes as biocontrol agents and biofertilizers manuring

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'

Multiple choice zoology microbes in human welfare biofertilizers microbes as biocontrol agents and biofertilizers manuring

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'.

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Heterocysts are considered as a site of nitrogen fixation in nitrogen-fixing BGA as they possess

  1. RuBISCO

  2. PEP carboxylase

  3. Nitrogenase

  4. Zymase
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Heterocysts are specialized nitrogen fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as Nostoc punctitorme, Cylindrospermum stagnale and Anabaena sphaerica. They fix nitrogen from dinitrogen in the air using the enzyme nitrogenase, in order to provide the cells in the filament with nitrogen for biosynthesis.
So, the correct answer in 'Nitrogenase'.
Multiple choice zoology microbes in human welfare biofertilizers microbes as biocontrol agents and biofertilizers manuring

Which statements are true about heterocyst?
(a) Thick cell wall is permeable to oxygen
(b) It lacks PS-II
(c) PS-I remains active which generates ATP required to fix nitrogen.

  1. All except (a)

  2. All except (b)

  3. All except (c)

  4. All (a), (b) and (c)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
1) heterocyst cells with thick cell films to prohibit oxygen. 
2) heterocysts do not have a utilitarian photosystem II. 
3) The settled carbon and nitrogen sources are traded through diverts between the cells in the fiber. Heterocysts keep up photosystem I, enabling them to create ATP by cyclic photophosphorylation as there is no release of $O _2$
So, the correct answer is 'All except (a)'