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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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'.
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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)'
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How many of the following organisms can be used as biofertilizers?
Azolla, Thiobacillus, Frankia, Glomus, Pseudomonas, Anthoceros, Klebsiella.

  1. $3$
  2. $5$
  3. $2$
  4. $1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Among the list, Azolla, Frankia, and Glomus are commonly used as biofertilizers. Thiobacillus, Pseudomonas, Anthoceros, and Klebsiella are generally not classified as standard agricultural biofertilizers in this context.

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Which of the following is correct?

  1. Cyanobacteria makes mycorrhiza which absorbs phosphate from soil

  2. Azotobacter is symbiotic nitrogen fixing bacteria

  3. In paddy field, cyanobacteria is used to decrease soil microbes

  4. Methanobacterium feed cellulose in anaerobic condition
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Certain bacteria, which grow anaerobically on cellulosic material, produce a large amount of methane along with $CO _2$ and $H _2$. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. 
  • These bacteria are present in the rumen (a part of the stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In the rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. 
  • Hence Methanobacterium feed cellulose in the anaerobic condition is a true statement.
  • So, the correct answer is 'Methanobacterium feed cellulose in anaerobic condition'.
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Which of the following is a non-symbiotic biofertilizer?

  1. VAM

  2. Azotobacter

  3. Anabaena

  4. Rhizobium
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Nitrogen is the important nutrient for plant growth. Plant obtains nitrogen from the atmosphere with the help of symbiotic and free nitrogen-fixing microorganisms. Azotobacter  is aerobic free living nitrogen fixing organism and fixes atmospheric nitrogen non-symbiotically. Therefore, all plants, trees, vegetables get benefited. Whereas VAM, Anabaena and Rhizobium are the symbiotic organisms. 

Thus, the correct answer is option B.

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The specialized structures in blue algae which fixes atmospheric nitrogen is called

  1. Heterocyst

  2. Endospore

  3. Oospore

  4. Conidiospore
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
A heterocyst is a differentiated cyanobacterial cell that carries out nitrogen fixation under aerobic conditions. They are formed in response to a lack of fixed nitrogen.
Whereas an endospore is a dormant, tough, non-reproductive structure produced by a small number of bacteria from the Firmicute family. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress.
An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and Oomycetes. In Oomycetes, oospores can also result from asexual reproduction, by apomixis.
Conidiospore - an asexually produced fungal spore formed on a conidiophore. Thus, the correct answer is option A.
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Which of the following is a biofertilizer?

  1. Funaria

  2. Fern

  3. Anabaena

  4. Fungus
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Blue-green alga like Nostoc, Anabaena fix atmospheric nitrogen and hence enhance soil fertility. Hence, these organisms are used as biofertilizers. Blue-green alga has special thick-walled cells, called as heterocysts, which carry on the process of fixation of atmospheric nitrogen.

So, the correct answer is option C.

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Leghaemoglobin takes part in

  1. Energy release

  2. Stimulating growth of Rhizobium
  3. N$ _{2}$ absorption

  4. Protecting nitrogenase

  5. Supply of oxygen
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pink color, typical of healthy and effective nodules, is due to the presence of a protein called leghemoglobin. This special protein contains Iron (Fe) and molybdenum (Mo) and is responsible for binding oxygen. This provides sufficient oxygen for the metabolic functions of the bacteroids but prevents the accumulation of free oxygen that would destroy the activity of nitrogenase.

So, the correct answer is option D.

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Find out the pairs, which are correctly matched.
A. Cyanobacteria                      (i.) Biopesticides
B. Mycorrhiza                          (ii.) Solubilization of phosphate
C. Bacillus thuringiensis          (iii.) Cry protein
D. Single cell protein               (iv.) Rhizobia

  1. A and ii.

  2. C and iii

  3. C and iv

  4. A and iii

  5. B and i
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Bacillus thuringiensis (Bt) is commonly used as a biopesticide. It is sporulating, a gram-positive facultative-aerobic soil bacterium. It synthesizes the proteins known as delta endotoxins or cry proteins which infect the insects by paralyzing the digestive tract and makes it porous.

So, the correct answer is option B.

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Cyanobacterial cells which are specialized for nitrogen fixation are

  1. Phycobilisomes

  2. Heterocysts

  3. Hormogonia

  4. Trichomes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Anabaena is a cyanobacteria. It has ability to fix atmospheric nitrogen. It converts nitrogen into ammonia. The heterocysts present in it are specialized cyanobacterial cells for nitrogen fixation. It contains enzyme nitrogenase. Nitrogenase is inactivated by oxygen. Hence, the heterocyst creates a micro anaerobic environment.

Thus, the correct answer is 'Heterocysts.'

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.......... are nitrogen fixing, aerobic, photosynthetic and Gram $(-)$ bacteria

  1. Archaebacteria

  2. Cyanobacteria

  3. Chlorobacteria

  4. Rickettsiae
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Cyanobacteria are photosynthetic prokaryotes that possess the ability to fix atmospheric nitrogen. They are Gram-negative and contain chlorophyll a, which allows them to perform oxygenic photosynthesis.

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Cyanobacteria are useful biofertilizers in fields of

  1. Wheat

  2. Maize

  3. Rice

  4. Sugarcane
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cyanobacteria are also called as Blue green algae. They are prokaryotic bacteria. They are nitrogen fixing bacteria. They are capable of fixing atmospheric nitrogen into ammonium compounds and making it available to the plants. They are useful bifertilizers in fields of rice for cultivation. They are used either free-living and in symbiotic association.

Thus, the correct answer is 'Rice.'