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 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'  

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

Leguminous plants are able to fix atmospheric nitrogen through the process ofsymbiotic nitrogen fixation. Which one of the following statements is not correct for this process of nitrogen fixation?

  1. Leghaemoglobin scavenges oxygen and is pinkish in colour.

  2. Nodules act as sites for nitrogen fixation.
  3. The enzyme nitrogenase catalyses the conversion of atmospheric $N _2$ to $NH _3$.

  4. Nitrogenase is insensitive to oxygen.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The nitrogenase enzyme is extremely sensitive to oxygen and is inactivated by it. Therefore, the statement that it is 'insensitive to oxygen' is incorrect.

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

Leguminous plants are important in agriculture because

  1. They are disease resistant

  2. They have high amounts of proteins

  3. They require less nitrogen for growth

  4. Nitrogen fixing bacteria are symbiotically associated in them
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Leguminous plants are important in agriculture because they contribute to nitrogen fixation. They contain symbiotic nitrogen-fixing bacteria within the nodules that produce nitrogen compounds that help the plant to grow. When the plant dies, the fixed nitrogen is released, making it available to other plants and this helps to fertilize the soil.
So the correct answer is 'Nitrogen-fixing bacteria are symbiotically associated in them'.
Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

The pigment protein present in nodulated roots inhabited by Rhizobium is

  1. Nitrate reductase

  2. Hydrogenase

  3. Leghaemoglobin

  4. Plastocyanin
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Rhizobium is symbiotic nitrogen-fixing bacteria present in the roots of leguminous plants. This bacteria is responsible for the formation of root nodules in legumes roots. The nodule contains a biochemical pigment protein called leg-haemoglobin that function as an oxygen scavenger.
so the correct answer is 'Leghaemoglobin'.