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

Nitrifying bacteria _________________.

  1. Oxidize.2riimonia to nitrates

  2. Convert free nitrogen to nitrogen compounds

  3. Convert proteins into ammonia

  4. Reduce nitrates to free nitrogen
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nitrifying bacteria oxidize ammonia to nitrites and then to nitrates in a two-step process. Nitrosomonas converts ammonia to nitrite, and Nitrobacter converts nitrite to nitrate. This is part of the nitrogen cycle.

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

Nitrifying bacteria are able to 

  1. Convert atmospheric nitrogen into soluble forms

  2. Convert ammonia to nitrate

  3. Ammonia to nitrogen

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

Nitrification is an important process in nitrogen cycle in nature, which is brought about by nitrifying bacteria. In warm moist soils having a temperature of $30-35^0$C and neutral pH, ammonia gets oxidized to nitrite ($NO _2^-$) and then nitrate ($NO _3^-$) by the process of nitrification. 

Nitrifying bacteria like Nitrosomonas convert ammonia to nitrite and another bacterium, called as Nitrobacter converts nitrite to nitrate.

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

The common nitrogen-fixer in paddy field is _______________.

  1. Azospirillum

  2. Oscillatoria

  3. Frankia

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

The common Nitrogen fixer in the paddy field is Azospirillum. This is a soil and root bacteria. It is a nitrogen-fixing bacteria when added to the soil it multiplies and supplies 30-40Kg nitrogen per hectare per season. It also produces Indole acetic acid which helps in growth.


Hence the correct option is A.

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'.