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 bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

The microorganisms that play an important role in maintaining the balance of nitrogen gas in the atmosphere are ________

  1. Bacteria

  2. Algae

  3. Virus

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

Rhizobium and Cynobacteria are involved in nitrogen fixation. There are many more bacteria like Nitrobacter, Nitrosomanas etc involve in maintaining the balance of nitrogen gas in the atmosphere.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

The bacteria present in root nodules of leguminous plants that fix the atmospheric nitrogen is

  1. Rhizobium

  2. Blue-green algae

  3. Nitrifying bacteria

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

Rhizobium is a bacterium found in the root nodules of leguminous plants. It induces the formation of special structures called nodules inside which it fixes atmospheric nitrogen. It does this with the help of nitrogenase enzyme that converts of nitrogen to ammonium that is an important factor required for plant growth. In turn, the bacterium receives shelter from the plant. Thus the correct answer is option A.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Oxidation of Ammonia into nitrite is performed by


(a) Nitrosomonas (b) Nitrosococcus (c) Nitrobacter (d) Nitrospira

  1. a, b

  2. b, c

  3. c, d

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

Oxidation of Ammonia to nitrite is performed by two groups of bacteria. Nitrosomonas and Nitrosocossus are examples of bacterias which perform the oxidation of ammonia to nitrite.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Nitrifying bacteria convert the

  1. Nitrates into nitrites

  2. Nitrites into nitrates

  3. Ammonium salts into nitrates

  4. Ammonium salts into amino acids
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Nitrification is a process of conversion of ammonium salts to nitrites and nitrites to nitrates. The bacteria that carry out this process are called as nitrifying bacteria. Nitrosomonas, Nitrosospira, Nitrosococcus convert ammonia into nitrites. Nitrobacter, Nitrospina, Nitrococcus convert nitrites into nitrates.

Thus, the correct answer is 'Ammonium salts into nitrates.'

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Nitrosomonas and Nitrobacter convert

  1. Carbon dioxide to carbohydrates

  2. Ammonium ion into nitrate

  3. Nitrate ion into nitrogen molecule

  4. Nitrogen into nitrate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Nitrification is a process of conversion of ammonium ions to nitrites and nitrites to nitrates. The bacteria that carry out this process are called as nitrifying bacteria. Nitrosomonas, Nitrosospira, Nitrosococcus convert ammonia into nitrites. Nitrobacter, Nitrospina, Nitrococcus convert nitrites into nitrates.

Thus, the correct answer is 'Ammonium ion into nitrate.' 

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

The common nitrogen fixer organism in paddy fields is

  1. Azospirillum

  2. Oscillatoria

  3. Frankia

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

Atmospheric nitrogen is not available to plants. There are certain nitrogen fixing bacteria which converts atmospheric nitrogen into ammonium compounds and make it available to the plants. Examples include Azotobacter, Frankia, Rhizobium, Azospirillum. Out of these, Azospirillum is widely used as nitrogen fixer organism in paddy fields. It is used as biofertilizer in rice fields. It promotes the plant growth.

Thus, the correct answer is 'Azospirillum.'

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Nitrite is changed to nitrate by

  1. Nitrobacter

  2. Nitrosomonas

  3. Clostridium

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

There are two steps in nitrification process by which ammonia is converted into nitrite and nitrite into nitrate. The bacteria that convert ammonia to nitrites include Nitrosomonas, Nitrosospira and the bacteria that convert nitrites to nitrates include Nitrobacter, Nitrospina. 

Thus, the correct answer is 'Nitrobacter.'

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Carefully read the following reactions carried out by nitrifying bacteria. Identify the statement about these equations which is not true.
2NH$ _3$+3O$ _2$ $\rightarrow$ 2NO$^- _2$ +2H$^+$ +2H$ _2O$ ---- (I)
2NO$^- _2$+O$ _2$ $\rightarrow$ 2NO$^- _3$ ---- (II)

  1. Step I is carried out by Nitrosomonas or Nitrosococcus

  2. Step II is carried out by Nitrobacter

  3. Both the steps I and II can be called nitrification

  4. Both the steps occur only in photoautotrophs
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
I) In the first step, ammonia is oxidised to nitrites by the action of nitrosomonas and nitrococcus bacteria.
II) In the second step, nitrate is further oxidised to nitrate with the help of nitrobacter and nitrocystis.
Both the reaction is involved in the process of nitrification. These nitrifying bacteria involved are called chemoautotrophs.
So the correct answer is 'Both the steps occur only in photoautotrophs'.
Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which one is not a free living nitrogen fixer?

  1. Rhodospirillum

  2. Azotobacter

  3. Rhizobium

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

The organisms involved in nitrogen fixation are termed as nitrogen-fixing organisms. They convert free nitrogen (gaseous form dinitrogen, N2) into forms such as nitrates and nitrites that can be utilized by plants. These organisms could either be free-living or found in symbiotic, mutualistic, or commensalistic relationships with other plants etc. Rhizobium is found in a symbiotic relationship with plant roots. 

So, the correct answer is 'Rhizobium'.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which of the following is free-living bacteria responsible for nitrogen fixation 

  1. Pseudomonas

  2. Rhodospirillum

  3. Azotobacter

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Nitrogen-fixing microorganisms are recognized: free-living (non-symbiotic) bacteria, including the cyanobacteria. Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium and mutualistic bacteria such as Rhizobium, associated with leguminous plants.

So, the correct option is 'All of these'.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

In the process of nitrification, ammonia is first oxidized to nitrite by

  1. Nitrosomonas and Nitrosococcus

  2. Nitrosomonas and Nitrobacter

  3. Pseudomonas and Nitrosococcus

  4. Pseudomonas and Thiobacillus
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

First step, ammonium ions are oxidised to nitrites. Nitrosomonas  are the  most important agents of oxidation of ammonia to nitrite in soil. Certain other bacteria are Nitrosococcus , Nitrosolobus ,etc.

Second step , oxidation of nitrite to nitrate takes place by Nitrobacter. 
So the correct option is "Nitrosomonas and Nitrococcus".

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which of the following is a symbiotic nitrogen fixer ?

  1. Azolla

  2. Glomus

  3. Azotobacter

  4. Frankia
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. Frankia is a nitrogen-fixing bacterium that lives in the soil and has a symbiotic relationship with many plants. Frankia is a genus of nitrogen-fixing, filamentous bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobium bacteria found in the root nodules of legumes in the family Fabaceae.

So, the correct answer is 'Frankia'.