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

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

How many organisms In the list given below are $N _2$ fixer autotrophs?
Azotobacter, Chromobum, Azospirillum, Rhodospirillum, Rhizobium, Nitrobacter, Aulosira, Nostoc, Osallatona

  1. Three

  2. Four

  3. Five

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

Nitrogen-fixing bacteria are capable of fixing atmospheric nitrogen to inorganic substances usable by plants. Example from the given list are Azetobactor, Azospirillum, Rhizobium, Nitrobactor and Nostoc.

So the correct answer is 'five'.

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

Which of the following is a free living aerobic non - photosynthetic nitrogen-fixer ?

  1. $Rhizobium$
  2. $Azotobacter$
  3. $Azospirillum$
  4. $Nostoc$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Azotobacter is a free-living nitrogen-fixing bacterium, which is used as a biofertilizer in the cultivation of most crops. Azotobacter respires aerobically, receiving energy from redox reactions, using organic compounds as electron donors. Azotobacter can use a variety of carbohydrates, alcohols, and salts of organic acids as sources of carbon. 

Rhizobium fixes nitrogen by symbiotic association. Nostoc is photosynthetic. Azospirillum is anaerobic. 
So, the correct option is 'Azotobacter'.

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

All of the following statements concerning the actinomycetous filamentous soil bacterium Frankia are correct except that Frankia

  1. Can induce root nodules on many plant species

  2. Can fix nitrogen in the free-living state

  3. Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex

  4. Forms specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Frankia is a bacterium which grows in a symbiotic association with the roots of non-leguminous plants.  It can fix atmospheric nitrogen. It cannot fix nitrogen in free-living state.

So, the correct option is 'Can fix nitrogen in free-living state'.

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

Bacteria involved in two-step conversion ammonia into nitrate are

  1. Azotobacter and Nitrosomonas

  2. Pseudomonas and Nitrobacter

  3. Azotobacter and Achromobacter

  4. Nitrosomonas and Nitrobacter
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Nitrification is a process of conversion of ammonium ions to nitrites and nitrites to nitrates. It is a two-step process. 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 'Nitrosomonas and Nitrobacter.' 

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

Which gene cluster is responsible for nitrogen fixation in bacteria?

  1. Nod, Nif, Nfx

  2. Nod, Nif, Fix

  3. Nod, Ndf, Nfx

  4. Ndx, Nif, Fix

  5. Ndx, Nif, nix
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Nitrogen fixation is a process by which nitrogen present in the atmosphere is converted into ammonia. It is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing compounds. This process is done with the help of nitrogen-fixing bacteria that have Nod, Nif and Fix gene clusters responsible for nitrogen fixation.
So the correct answer is 'Nod, Nif, Fix'.
Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Match the columns and choose the correct option.

I II
(a) Free-living aerobic nitrogen fixers 1. Anabaena and Nostoc
(b) Anaerobic nitrogen fixers 2. Pseudomonas and Thiobacillus
(c) Nitrogen-fixing cyanobacteria 3. Nitrosomonas and Nitrosococcus
(d) Denitrifying bacteria 4. Azotobacter and Beijerinckia
(e) Nitrifying bacteria 5. Rhodospirillum

  1. a - 4, b - 5, c - 1, d - 2, e - 3

  2. a - 5, b - 4, c - 1, d - 3, e - 2

  3. a - 4, b - 5, c - 2, d - 3, e - 1

  4. a - 4, b - 3, c - 1, d - 2, e - 5

  5. a - 4, b - 5, c - 3, d - 2, e - 1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
a) Free-living aerobic nitrogen fixers - Azotobacter and Beijernikia
b) Anaerobic nitrogen fixers - Rhodospirillum
c) Nitrogen-fixing cyanobacteria - Anabaena and Nostoc
d) Denitrifying bacteria - Pseudomonas and Thiobacillus
e) Nitrifying bacteria - Nitrosomonas and Nitosococcus
So the correct answer is 'a-4, b-5, c-1, d-2, e-3'
Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which of the following is the function of nitrifying bacteria?

  1. Oxidise $NH _3$ to $NO^- _3$
  2. Oxidise $NH _3$ to $NH^+ _4$
  3. Convert $NO^- _3$ to $NH _3$
  4. Convert $NO^- _3$ to $N _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Nitrifying bacteria is an aerobic bacteria that use inorganic chemicals as an energy source. They are important in the nitrogen cycle as converters of soil ammonia to nitrates by the process of oxidation.
So the correct answer is 'oxidise NH$ _3$ to NO$ _3$-'.
Multiple choice chemistry chemistry in daily life food spoilage and food preservation methods of preserving food chemicals in food

It is found in phosphorus and nitrogen

  1. inorganic impurities

  2. bacteria

  3. nutrients

  4. other microbes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Nitrogen and phosphorous are nutrints that are natural parts of aquatic ecosystems.Nitrogen is also most abundant element in the air we breath nitrogen and phosphorous support the growth of a lgee and aquatic plants,which prouide food and habbit for fish and smaller organisma that line in water.