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

The nodules present in the leguminous plants appear pink in colour due to the presence of 

  1. RBC.s

  2. leghaemoglobin

  3. nitrogenase enzyme

  4. bacterial secretion
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Leghaemoglobin is an oxygen-binding protein found in the root nodules of leguminous plants. It gives the nodules their characteristic pink or red color.

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

Which of the following statements is incorrect about leghaemoglobin?

  1. It acts as $O _2$ scavenger

  2. It imparts pink or red colour to the nodules
  3. It combines with $O _2$ and protects nitrogenase

  4. It is a Mo-Fe protein.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Leghaemoglobin is an iron-containing protein (a hemoprotein), not a Molybdenum-Iron (Mo-Fe) protein. Nitrogenase is the Mo-Fe protein involved in nitrogen fixation.

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

Read the following statements and select the correct answer: - 


(i) Rhizobium leguminosarum is also known as Bacillus radicicola.
(ii) Nitrifying bacteria (Nitrosomonas, etc) are chemoautotrophs.
(iii) Enzyme nitrogenase fixes $N _2$ under aerobic conditions.
(iv) Leghaemoglobin creates aerobic conditions for the enzyme nitrogenase. 

  1. Statements (i), (ii) and (iii) are correct

  2. Statements (i) and (ii) are correct

  3. Statements (iii) and (iv) are correct

  4. All statements are correct
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Statements I and ii are correct. Rhizobium leguminosarum is also known as Bacillus radicicola. Nitrifying bacteria (Nitrosomonas, etc) are chemoautotrophs. They use inorganic energy sources. However, the enzyme nitrogenase is highly sensitive to oxygen and gets readily oxidised in it's presence and Leghaemoglobin creates anerobic conditions for the enzyme nitrogenase by scavenging the oxygen molecules.

Thus, the correct answer is 'Statements (i) and (ii) are correct.' 

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

Biofertilizers are organisms that enrich the nutrient quality of the soil. Which of the following can be used as biofertilisers ?

  1. Nitrogen fixing cyanobacteria

  2. Nitrogen fixing bacteria

  3. Mycorrhizae

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Nitrogen fixing cyanobacteria, Nitrogen fixing bacteria and mycorrhizae all can be used as biofertilisers as they all enrich the nutrient quality of the soil.
So, the correct option is 'All of these'
Multiple choice evs a seeds tells a farmer's story manure manures and fertilisers water absorption organ

If by radiation all nitrogenase enzyme is inactivated, then there will be no.

  1. fixation of nitrogen in legumes

  2. conversion of nitrate into nitrogen

  3. conversion from nitrate to nitrate in legumes

  4. conversion from ammonium to nitrate in soil
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nitrogenase is the essential enzyme for biological nitrogen fixation. If it is inactivated, the plant cannot convert atmospheric nitrogen into ammonia.

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

Organisms which can bring about soil nutrient enrichment are known

  1. sympathetic bacteria

  2. Biofertilizers

  3. Soil bacteria

  4. Proxy fertilizers
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Through the use of biofertilizers, healthy plants can be grown, while enhancing the sustainability and the health of the soil. ... Biofertilizers such as Rhizobium, Azotobacter, Azospirilium and blue green algae (BGA) have been in use a long time. Rhizobium inoculant is used for leguminous crops. So, the correct option is "B" (Biofertilizers).

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

Favourable condition for nitrogenase activity in heterocyst of BGA is due to

  1. Loss of PS-II

  2. Loss of PS-I

  3. Presence of thick wall

  4. More than one option is correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heterocysts are specialized nitrogen-fixing cells formed during nitrogen starvation by some blue-green algae. They fix nitrogen from di-nitrogen in the air using the enzyme nitrogenase and nitrogenase is inactivated by oxygen, so the heterocyst must create a micro-anaerobic environment and that's why heterocysts degrade photo-system II, which produces oxygen.

So, the correct option is 'Loss of PS-II'.

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

In root nodules of legumes, leghaemoglobin is important because it:-

  1. Acts as a catalyst in transamination

  2. Transports oxygen to the root nodule

  3. Provide energy to the nitrogen fixing bacteria

  4. Acts as an oxygen scavenger
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • Leghaemoglobin (also leghemoglobin or legoglobin) is an oxygen carrier and hemoprotein found in the nitrogen-fixing root nodules of leguminous plants. 
  • Leghaemoglobin buffers the concentration of free oxygen in the cytoplasm of infected plant cells to ensure the proper function of root nodules.

So, the correct answer is "transports oxygen to the root nodule".

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

Which one of the following can be used as a biofertilizer?

  1. Plasmodium

  2. Rhizobium

  3. Chenopodium

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

Microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Rhizobium can be used as biofertilizer. Rhizobium are found in the soil and after infection, produce nodules in the legume where they fix nitrogen gas (N2) from the atmosphere turning it into a more readily usable form of nitrogen.


So, the correct option is 'Rhizobium'.

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

Leghaemoglobin in symbiotic nodules helps :

  1. To provide energy to the growing symbionts

  2. In nitrogen reallocation between symbionts and plants

  3. By scavenging Oxygen

  4. To stabilize redox potential of host cells
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Leghaemoglobin helps to mantain internal oxygen in symbiotic nodules, because this protein has ten times more affinity for oxygen as compared to blood pigment haemoglobin.Therefore they acts as oxygen scavenger.

So, the correct answer as 'by scavenging oxygen'

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

The $N _{2}$ fixing bacterium associated with root nodules of legumes is known as

  1. Azotobacter

  2. Nitrobacter

  3. Lactobacillus

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

Rhizobium is microaerophilic rod shaped gram negative bacteria found in association with legume plants in root nodules. These bacteria fix atmospheric nitrogen into ammonium ions, which can be readily assimilated by plants.

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

The pigment useful in nitrogen fixation is

  1. Nitrogenase

  2. Haemoglobin

  3. Myoglobin

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

Plants cannot consume atmospheric nitrogen directly, because in atmosphere nitrogen occurs in stable diatomic form. The atmospheric nitrogen needs to be converted into plant usable forms like nitrate, nitrite and ammonium ion. This process is called as nitrogen fixation. 

Rhizobium is a microaerobic bacteria, which occurs in root nodules of legume plants in symbiotic association. Rhizobium bacteria nodule is pink coloured due to presence of a bacterial pigment called as leghaemoglobin. This pigment binds excess oxygen present in nodules. Free oxygen is harmful for the nitrogenase enzyme of Rhizobium. Rhizobium bacteria reduces atmospheric nitrogen into ammonium ions using reducing power obtained from host plant.

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

Function of leghaemoglobin during biological nitrogen fixation in root nodules of legumes is to _________________.

  1. Convert atmospheric ntirogen to ammonia

  2. Convert ammonia to nitrogen

  3. Transport oxygen for activity of nitrogenase

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

The primary function of leghaemoglobin is to bind oxygen, thereby protecting the oxygen-sensitive nitrogenase enzyme from inactivation.