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

What's true about atmospheric nitrogen?

  1. It has the formula N3.

  2. It is useful for plants as they grow.

  3. It is the second most abundant atmospheric gas after oxygen.

  4. It has to be fixed by bacteria in order to be useful.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Atmospheric nitrogen (N2) is inert and cannot be used directly by plants. It must be 'fixed' by bacteria into forms like ammonia or nitrates to be biologically useful.

Multiple choice

What's the function of nitrogen-fixing bacteria?

  1. convert N2 into soil nitrogen

  2. convert carbon into nitrogen

  3. convert soil nitrogen into N2

  4. convert nitrate into nitrite
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into ammonia or other compounds in the soil that plants can absorb.

Multiple choice

What's the function of denitrifying bacteria?

  1. convert N2 into soil nitrogen

  2. convert carbon into nitrogen

  3. convert soil nitrogen into N2

  4. convert nitrate into nitrite
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Denitrifying bacteria convert nitrates in the soil back into nitrogen gas (N2), releasing it into the atmosphere.

Multiple choice

The nitrogen fixing bacteria are

  1. Rhizobium

  2. Aztobacter

  3. Cyno bacteria

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

Rhizobium, Azotobacter, and Cyanobacteria are all known for their ability to fix atmospheric nitrogen into a form plants can use. Therefore, 'All of these' is correct.

Multiple choice zoology global environmental change causes of greenhouse effect greenhouse effect pollution and its effects

Denitrification is caused by

  1. Pseudomonas

  2. Nitrobacter

  3. Nitrosomonas

  4. Azotobacter
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Denitrification is the process of degradation of fixed nitrogenous compounds to free nitrogen which is released back to the atmosphere. It is performed by several bacteria like Pseudomonas which utilize nitrate to form nitrite in a process called reduction. Nitrite is further reduced to nitric oxide then to nitrous oxide and then nitrogen gas. This process reduces the fertility and ultimately the agricultural productivity decreases.
Thus, the correct answer is option A.
Multiple choice chemistry synthetic fibres and plastics environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Substances which cannot be decomposed by micro-organisms are called non-biodegradable substances.

  1. True

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

Biodegradable substances are such materials which are and can be degraded by natural factors like microbes (e.g. bacteria, fungi and few more), abiotic elements like temperature, UV, oxygen, etc.
Unlike biodegradable, non-biodegradable substances like plastics, cannot be easily handled and cannot be decomposed or dissolved by natural agents.
Option A is correct

Multiple choice biology improvement in food resources manure manures and fertilisers role of organic manures in soil management

Rhizobium fixes atmospheric _____________

  1. Oxygen

  2. Carbon

  3. Nitrogen

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

  • Rhizobium is the symbiotic soil bacteria that fix nitrogen in leguminous plants. They form a symbiotic relationship with legume and resides in the root nodules of legumes. 
  • They cannot independently fix nitrogen. 

Therefore, the correct answer is option C.

Multiple choice biology improvement in food resources manure manures and fertilisers role of organic manures in soil management

Consider the following microbes

A. Azotobacter
B. Azolla
C. Mycorrhiza
D. Nostoc

The aforementioned microbes are

  1. Manure yielding biofertilizers

  2. Converters of atmospheric nitrogen into ammonia

  3. Capable of improving the elements phosphorus, potassium, zinc etc., in soil

  4. The source of nitrogenous fertilizer
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • Azotobacter, Azolla, Mycorrhiza, and Nostoc are manure yielding biofertilizers. Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi, and cyanobacteria.
  • Azotobacter is bacteria that can fix atmospheric nitrogen while free-living in the soil, thus enriching the nitrogen content of the soil.
  • Azolla is a water fern. It lives in a symbiotic relationship with a cyanobacteria Anabaena azollae which fixes nitrogen. It is used as an excellent fertilizer in the rice field.
  • Mycorrhiza is a symbiotic relationship of fungi with roots of higher plants. The fungal symbiont absorbs phosphorus from soil and passes it to plants. Plants having such associations show resistance to root borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.
  • Nostoc is a cyanobacterium. It can fix atmospheric nitrogen. It also adds organic matter to the soil and increases its fertility. 

Multiple choice biology natural resources and agriculture manure manures and fertilisers role of organic manures in soil management

Which of the following statements are correct?

A. Ammonia is the major source of nitrogenous fertilizer in plants.
B. Biofertilizer culture of Azotobacter is available in the market and it is highly effective for crops like coconut, tapioca, sugar cane, etc.
C. The special type of cell known as heterocyst present in the blue-green algae is responsible for atmospheric nitrogen fixation in Azolla.
D. Mycorrhizal fungi help the plants receive phosphorus fertilizer.

  1. C and D

  2. A and C

  3. A, B and C

  4. A, B, C and D
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Some ammonia is converted into nitric acid which itself is used in the manufacture of fertilizers and explosives. Ammonia is also a useful ingredient in some cleaning fluids. Ammonia is a vital route by which nitrogen in the air can be made available to plants to enable them to build protein molecules.
Biofertilizers
 (i) They help in the establishment and growth of crop plants and trees.
 (ii) They enhance biomass production and grain yields by 10-20 percent. 
(iii) They are useful in sustainable agriculture. 
(iv) They are suitable for organic farming.
Azotobacter
Application of Azotobacter has been found to increase the yield of coconut, tapioca, sugarcane, wheat, rice, maize, pearl millet and sorghum by 0-30 p.c. over control. Apart from nitrogen, this organism is also capable of producing antifungal and antibacterial compounds, hormones.
Azospirillum
Certain micro-organisms like bacteria and blue-green algae have the ability to use atmospheric nitrogen and transport this nutrient to the crop plants. Azospirillum is inoculated to maize, barley, oats, sorghum, pearl millet, and forage crops. It increases the grain productivity of cereals by 5-20%, of millets by 30% and fodder by over 50%.
Blue-green algae
- The utilization of blue-green algae as a biofertilizer for rice is very promising. A judicious use of these algae could provide to the country’s entire rice acreage as much nitrogen as obtained from 15-17 lakh tones of urea. Algae also helps to reduce soil alkalinity.
Azolla
A small floating water form Azolla is commonly seen in low land fields and in shallow freshwater bodies. This fern harbors a blue-green algae. Anabaena azollae The Azolla – Anabaena association is alive floating nitrogen factory using energy from photosynthesis to fix atmospheric nitrogen accounting to 100-150 kg N/ha/year from about 40 – 60 tones of biomass.
Mycorrhizae:
It is the symbiotic association of fungi with the roots of vascular plants. It is useful in increasing phosphorus uptake e.g. in fruit crops like citrus, papaya.
So, the correct answer is 'A, B, C and D'
Multiple choice biology natural resources and agriculture manure manures and fertilisers role of organic manures in soil management

The high protein content of legumes(pluses) is correlated with.

  1. Application of fertilizers to the soil

  2. Nitrogen content of the soil

  3. Nitrogen-fixing bacteria present in the roots

  4. Their tropical or temperate origin
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Legumes contain high amounts of protein because their root nodules host symbiotic nitrogen-fixing bacteria, such as Rhizobium. These bacteria convert atmospheric nitrogen into ammonia, which the plant uses to synthesize amino acids and proteins.

Multiple choice zoology sustainable agriculture microbes and farming biopesticide environmental protection

Select the correct statement from the following 

  1. Flavobacterium is used to control 2,4-D

  2. Enterobacter aerogenes is used to control DDT

  3. Superbug is used to control oil spill

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • 2,4-Dichlorophenoxyacetic acid (2,4-D) is the third most commonly used herbicide all over the world.  The health hazards of 2,4-D to humans include that it may induce cytogenetic damage in human lymphocytes, irreversible eye damage, hepatotoxicity and nephrotoxicity. Many methods are proposed for treatment of chemical pollution, however, the safest and the cheapest one is the use of microorganisms for biodegradation of these pollutants. the most biologically active strains against 2,4-D proved to belong to the genera Pseudomonas, Achromobacter, Flavobacterium, Nocardia, Streptomyces and Aspergillus.
  • 1,1,1 -trichloro-2,2-bis (p-chlorophenyl)ethane (DDT) is one of the best synthetic pesticides. It was used to control mosquitoes spreading malaria, typhus and other insect-borne diseases among both military and civilian populations. After the war, DDT was made available for use as an agricultural insecticide. It was used extensively for the control of grass grub {Costelytra zealandica White). It was necessary to introduce microbes to degrade or control DDT in soil. It was done so by using DDT-degrading strain of E. aerogenes.
  • So all the above options are correct.
Multiple choice zoology sustainable agriculture microbes and farming biopesticide environmental protection

Find out the pairs which are correctly matched.

a Cyanobacteria $1$ Biopesticide
b Mycorrhiza $2$ Solubilisation of phosphate
c Bacillus thuringiensis $3$ Cry protein
d Single cell protein $4$ Rhizobia
  1. A and $2$
  2. B and $3$
  3. C and $3$
  4. A and $3$
  5. B and $4$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Bacillus thuringiensis have Bt toxin encoded by cry genes forming cry proteins.

 Correct answer-C