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 evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

In what family of plants is nitrogen usually fixed ?

  1. Coniferous trees

  2. Sea Grass

  3. Legumes

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

In the roots of legumes, there live many bacteria, who through their own metabolic processes are able to convert the nitrogen gas into ammonia or ammonium, depending on the acidity of the soil. Converting nitrogen gas into a more usable form is extremely difficult and is the reason that this process is so specialized. While ammonium may be usable by a few plants, the majority cannot use it and another process is required. Nitrifying bacteria oxidize the ammonia creating nitrite then nitrate allowing for the nitrogen to be assimilated into the plants.

So, the correct answer is 'Legumes'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Leghaemoglobin helps in

  1. Nitrogen fixation
  2. Protecting nitrogenase from O${ _2}$

  3. Killing bacteria

  4. Transport of food in plants
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Many rhizobia, nitrogen fixing bacteria, live in a symbiotic relationship with plants known as legumes. In such plants, the presence of oxygen in the root nodules would reduce the activity of the oxygen-sensitive nitrogenase. In these situations, the roots of such plants produce a protein known as leghemoglobin. Leghemoglobin buffers the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules. Leghemoglobin is a nitrogen or oxygen carrier; naturally occurring oxygen and nitrogen interact similarly with this protein. Hence option B is correct.

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

The function of leghaemoglobin during biological nitrogen fixation, in root nodules of legumes is to

  1. Convert atmospheric N$ _2$ to NH$ _3$

  2. Convert ammonia to nitrite

  3. Transport oxygen for activity of nitrogenase

  4. Protect nitrogenase from oxygen
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Leghaemoglobin is an oxygen scavanger. It combines with oxygen and protects nitrogenase, which catalyses the fixation of nitrogen under anaerobic conditions.

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Which of the following microorganism is used to prepare biofertilizers? 

  1. Algae

  2. Protozoa

  3. Virus

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Biofertilizer is a substance that contains living organisms which is used to increase the fertility of the soil. It improves the growth of plant by increasing the availability of nutrients to the host plant. Various biofertilizers are Rhizobium, Azotobacter, blue green algae (BGA). Algae have ability of nitrogen fixation, therefore adding organic matter and extra nitrogen to the soil. This increases the soil fertility. 

Thus, the correct answer is option A.

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Which of the following is essential for nitrogen fixation in legumes?

  1. Anthocyanin

  2. Phycocyanin

  3. Phycoerythrin

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

Leguminous plants are in symbiotic association with nitrogen-fixing bacteria like Rhizobium. These bacteria invade root hairs of leguminous plants and forms root nodules in which they fix nitrogen. A red pigment present in the root nodules of leguminous plants is known as leghaemoglobin. Leghaemoglobin is an oxygen-carrier molecule.  It protects nitrogen-fixing enzyme nitrogenase from the side effect of oxygen as the enzyme is highly sensitive to oxygen.

Thus, the correct answer is 'Leghaemoglobin.'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Which of the following is correct about legumes?

  1. They are incapable of fixing nitrogen

  2. They fix nitrogen with the help of bacteria that live in their leaves

  3. They fix nitrogen with the help of bacteria that live in their roots

  4. They fix nitrogen independent of bacteria
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Legumes are in symbiotic association with nitrogen-fixing bacteria like Rhizobium. They fix nitrogen with the help of bacteria that live in their roots. These bacteria invade root hairs of leguminous plants and forms root nodules in which they fix nitrogen. Rood nodules are found in some other plants also apart from leguminous plants. A red pigment present in the root nodules of leguminous plants is known as leghaemoglobin. 

Thus, the correct answer is 'They fix nitrogen with the help of bacteria that live in their roots.'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

In root nodules of legumes, the role of leghemoglobin is

  1. To transports oxygen to root nodules

  2. To act as an oxygen scavanger

  3. To act as a catalyst in transamination

  4. To provide energy to nitrogen fixing bacteria
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Atmospheric nitrogen is not available to the plants. Nitrogen fixing bacteria converts atmospheric nitrogen into ammonium compounds and make it available to the plants. There are two types of bacteria, free-living and symbiotic. Example of free living nitrogen fixing bacteria include Azotobacter. The example of symbiotic nitrogen fixing bacteria includes Rhizobium. Rhizobium lives in symbiotic association with the legume plants in the root nodules and fixes atmospheric nitrogen. Root nodules of legume plants contains leghaemoglobin. This acts as an oxygen scavanger. 

Thus, the correct answer is 'Acts as an oxygen scavanger.'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

A red pigment present in the root nodules of leguminous plants is known as

  1. Phycoerythrin

  2. Bacteriochlorophyll

  3. Leghaemoglobin

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

Leguminous plants are in symbiotic association with nitrogen-fixing bacteria like Rhizobium. These bacteria invade root hairs of leguminous plants and forms root nodules in which they fix nitrogen. A red pigment present in the root nodules of leguminous plants is known as leghaemoglobin. Leghaemoglobin is an oxygen-carrier molecule.  It protects nitrogen-fixing enzyme nitrogenase from the side effect of oxygen as the enzyme is highly sensitive to oxygen.

Thus, the correct answer is 'Leghaemoglobin.'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Identify the role of lectins in formation of root nodules in legumes.

  1. Formation of shepherd's crook

  2. Recognition of compatible Rhizobium by host

  3. Formation of peribacterial membrane

  4. Formation of infection thread
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lectins are sugar-binding proteins that play a key role in the recognition and attachment of compatible Rhizobium bacteria to the root hairs of host leguminous plants.

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Function of red pigment leghaemoglobin present in root nodules of leguminous plants is to regulate

  1. $CO _2$ supply in cells

  2. Mo supply to cells
  3. $O _2$ supply to cells

  4. Production of phenolic compounds
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The root nodules of the leguminous plants contain an oxygen-binding heme protein called leghemoglobin. It is present in the cytoplasm of infected nodule cells at high concentrations. This leghemoglobin has a high affinity for oxygen, (approximately, ten times higher than the ß chain of human hemoglobin). Its function is to help transport oxygen to the respiring symbiotic bacterial cells in a manner analogous to hemoglobin transporting oxygen to respiring tissues in animals. Thus, it regulates oxygen supply to the cells.
Thus, the correct answer is option (C). 
Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Leghaemoglobin takes part in

  1. Energy release

  2. Stimulating growth of rhizobium
  3. $N _2$ absorption
  4. Protecting nitrogenase from $O _2$

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

The root nodules contain pink colored pigment contains a protein called leg-hemoglobin.

Leg-haemoglobin acts as an oxygen scavenger and provides anaerobic conditions to the bacteria.
So the correct answer is 'protecting nitrogenase from oxygen'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Leghaemoglobin occurs in

  1. Coralloid root

  2. BGA

  3. Around bacterial infections of root nodules

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

Leghaemoglobin is an oxygen carrier found in the nitrogen fixing root nodules of leguminous plants. Rhizobium is a free living bacteria that can fix atmospheric nitrogen.

Steps involved in nodule formation are
1.Rhizobium bacteria contact a susceptible root hair.
2.After this they will divide near it.
3.Then Rhizobium infects the root hair causing it to curl.
4.Infected thread carries the bacteria to the inner cortex.
5.The bacteria get modified into rod shaped bacteroids and cause inner cortical and pericycle cells to divide.
6.Division lead to nodule formation.
So the correct answer is 'Around bacterial infections of root nodules'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Apart from bacteria, which of the following microbes help in nutrient replenishment in the soil?

  1. Protozoa

  2. Fungi

  3. Virus

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

Protozoa play a major role in replenishing nutrients in the soil. Protozoa have a lower concentration of nitrogen in their cells than the bacteria they eat. Therefore, they obtain and utilize the amount of nitrogen needed and release the excess in the form of ammonium, thereby making it available for use by plants and other soil organisms.   

So the correct option is 'Protozoa'

Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

Which of the following helps the plant to absorb nitrogen from the environment?

  1. Algae

  2. Lichens

  3. Rhizobium

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Plants are not capable of fixing nitrogen on their own, but need it in one or the other form to make proteins and amino acids. Legumes form root nodules, when they exist in a symbiotic relationship with 'Rhizobia' and therefore, have high levels of nitrogen available to them. These soil bacteria (e.g., Rhizobium, Mesorhizobium, Sinorhizobium) fix the atmospheric nitrogen or dinitrogen, into inorganic compounds, like ammonium, which is then converted into amino acids, which the plants can utilize.

So the correct option is 'Rhizobium'