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 botany the living world archaebacteria the three domains of life classification of microbes

Which of the following bacteria is present in the rumen of cattle ?

  1. Azotobacfer

  2. Rhizoblum

  3. Methanobacterium

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

Methanobacterium is found in the rumen (a part of the stomach) of cattle. A lot of cellulosic material is also available in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in nutrition of cattle.

Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

Certain bacteria are able to thrive under extreme environmental conditions such as absence of oxygen, high salt concentration, high temperature or highly acidic environment. What are these bacteria called?

  1. Probacteria

  2. Neobacteria

  3. Hardy bacteria

  4. Archaebacteria
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Archaebacteria are the oldest organisms living on the Earth. They are unicellular prokaryotes and belong to the kingdom, Archaea. They were first discovered in 1977 and classified as bacteria. Most archaebacteria appear like bacteria, when observed under the microscope. However, they are quite different from bacteria and eukaryotic organisms. Archaebacteria are found in very harsh conditions such as in the volcanic vents or at the bottom of the sea. They can easily survive in such extreme environment as sea vents releasing sulfide-rich gases, hot springs, or boiling mud around volcanoes.
So the correct option is 'archaebacteria'.
Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

These bacteria grow anaerobically on cellulosic material, produce large amount of methane along with $CO _2$ and $H _2$ and are collectively called as methanogens. Examples of such bacteria are:

  1. Melhanobacterium

  2. Mathanobrevibacter

  3. Methanococcus

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

Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic condition. They include Methanobacterium, Methanobrevibacter and Methanococcus. 

Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

Marsh gas is produced by

  1. Mycoplasma

  2. Myxobacteria

  3. Methanogens

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

Marsh gas is also called as biogas. It is also called as methane gas as it primarily consists of methane gas along with hydrogen sulfide and carbon dioxide in minor composition. It is a produced by the decomposition of vegetable matter under water by anaerobic bacteria. The marsh gas is produced by Methanogens that are found in marshes.

Thus, the correct answer is 'Methanogens.'

Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

The group of bacteria devoid of peptidoglycan in its wall is

  1. Archaebacteria

  2. Cyanobacteria

  3. Eubacteria

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

Peptidoglycan is a polymer that is present in the cell wall of most bacteria. It is also called as Murein. However, Archaebacteria are devoid of peptidoglycan in its wall. Instead, they are made up of the polysaccharide called pseudomurein.

Thus, the correct answer is 'Archaebacteria.'

Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

State whether the following statements are true or false.
Azotobacter is a heterotrophic nitrogen fixing bacterium.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nitrogen fixing is seen in heterotrophic bacteria live in the soil and fix significant levels of nitrogen, species like Clostridium, Bacillus, Azotobacter are called nitrogen-fixing bacteria.

So, the correct option is 'True'.

Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

Bacteria which are found in marshy areas and among the flora of cattle rumen are called

  1. Acidophiles

  2. Thermophiles

  3. Methanogens

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

Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain of archaea. They are common in wetlands, where they are responsible for marsh gas, and in the digestive tracts of animals such as ruminants and humans, where they are responsible for the methane content of belching in ruminants and flatulence in humans. In marine sediments the biological production of methane, also termed methanogenesis, is generally confined to where sulfates are depleted, below the top layers. Moreover, the methanogenic archaea populations play an indispensable role in anaerobic wastewater treatments. Others are extremophiles, found in environments such as hot springs and submarine hydrothermal vents as well as in the "solid" rock of the Earth's crust, kilometers below the surface.

So the correct option is 'methanogens'.

Multiple choice botany the living world archaebacteria the three domains of life classification of microbes

Choose the correct answers from the alternatives given.
Facultative anaerobes:

  1. require a constant supply of oxygen

  2. are killed in an oxygenated environment

  3. do not always need oxygen

  4. are photosynthetic but do not give off oxygen
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to respiration if oxygen is absent.

So, the correct option is 'do not always need oxygen'.

Multiple choice botany bacteria bacteria - friend and foe useful and harmful bacteria bacteria; benefits and harmful effects

A free living nitrogen-fixing cyanobacterium which can also form symbiotic association with water fern Azolla is

  1. Anabaena

  2. Tolypothrix

  3. Chlorella

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

Anabaena belongs to the family of filamentous cyanobacteria that is known for its nitrogen fixing ability. While these exists as a plankton, it is known to form symbiotic relationships with the water fern Azolla and are found growing together at the surface of streams and ponds on temperate and tropical regions.
Therefore, the correct answer is option A.

Multiple choice botany bacteria bacteria - friend and foe useful and harmful bacteria bacteria; benefits and harmful effects

Which of the following is a free living nitrogen fixing bacteria present in the soil?

  1. Pseudomonas

  2. Rhizobium

  3. Azotobacter

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

Azotobacter has a wide variety of metabolic abilities, including the unusual ability to fix atmospheric nitrogen as they produce nitrogenase enzyme and convert it to ammonia. They are free living in soil and do not associate as symbionts. 

Multiple choice botany bacteria bacteria - friend and foe useful and harmful bacteria bacteria; benefits and harmful effects

Which of the following is the useful activity of several bacteria?

  1. Nitrogen fixation

  2. Nitrification

  3. Operation of biogeochemical cycles

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

Some bacteria can fix atmospheric nitrogen, e.g., Azotobacter and Clostridium, while others convert ammonia into nitrate, e.g., Nitrosomonas.
A biogeochemical cycle or substance turnover or cycling of substances is a pathway by which chemical nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and water etc move through both biotic and abiotic compartments of earth. All of these are required to carry out basic life processes as these processes supply with energy and nutrients. Thus, the correct answer is option D.

Multiple choice botany bacteria bacteria - friend and foe useful and harmful bacteria bacteria; benefits and harmful effects

A prokaryotic autotrophic nitrogen fixing symbiont found in

  1. Pisum

  2. Alnus

  3. Cycas

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

Cyanobacteria, which have "symbiotic" relationships with cycads are in the order Nostocales. Anabaena cycadeae is a blue green algae (BGA) commonly found in the coralloid roots of cycads. At first, the cycad sprouts without any cyanobacterium. Coralloid roots are formed soon after the primary root.
So answer is - 'Cycas'.

Multiple choice botany bacteria bacteria - friend and foe useful and harmful bacteria bacteria; benefits and harmful effects

The most abundant prokaryotes helpful to humans in making curd from milk and in production of antibiotics are the ones categorised as

  1. Cyanobacteria

  2. Archaebacteria

  3. Chemosynthetic autotrophs

  4. Heterotrophic bacteria
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Heterotrophic bacteria require an organic carbon source for growth (i.e., they derive energy and carbon from organic compounds). Economically important uses of heterotrophic bacteria are:

  1. They enhance the fertility of the soil by nitrogen fixation.
  2. Production of curd and yogurt from milk, cheese, butter, wine
  3. Production of antibiotics
  4. They form an essential part of biogeochemical cycles during which they release essential elements, such as nitrogen and carbon for recycling.
  5. Cleaning of oil spills
So answer is - 'Heterotrophic bacteria'.

Multiple choice botany bacteria bacteria - friend and foe useful and harmful bacteria bacteria; benefits and harmful effects

Bacteria which directly convert atmospheric nitrogen into nitrogen compounds are called as

  1. Denitrifying bacteria

  2. Putrefying bacteria

  3. Nitrogen fixing bacteria

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

Bacteria which directly convert atmospheric nitrogen into nitrogen compounds are called nitrogen fixing bacteria. They could be symbiotic or free- living like Rhizobium and Azotobacter respectively.
So answer is -'Nitrogen fixing bacteria'.