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 zoology bioenergy biogas environmental use of microorganism microbes in waste treatment and biogas

Identify the correct pair of characters of a bacterium which is used in the production of methane.
(i)   Recyclers of inorganic nutrients
(ii)  Present in stomach of cattle
(iii) Obtain energy from sunlight
(iv) Aerobes

  1. ii, iii

  2. i, ii

  3. i, iv

  4. iii, iv
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Methanogens are anaerobic bacteria (not aerobes) that recycle inorganic nutrients and are found in the rumen of cattle to aid in cellulose digestion.

Multiple choice zoology bioenergy biogas environmental use of microorganism microbes in waste treatment and biogas

The order of bacteria active in conversion of organic wastes into biogas is

  1. Hydrolytic $\rightarrow$ Acetogenic $\rightarrow$ Methanogenic
  2. Methanogenic $\rightarrow$ Acetogenic $\rightarrow$ Hydrolytic
  3. Methanogenic $\rightarrow$ Hydrolytic $\rightarrow$ Acetogenic
  4. Acetogenic $\rightarrow$ Methanogenic $\rightarrow$ Hydrolytic
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The order of bacteria active in the conversion of organic wastes into biogas is hydrolytic, acetogenic, methanogenic. 

Hydrolytic- Insoluble organic polymers, such as carbohydrates, are broken down to soluble derivatives which are used by bacteria.

Acetogenic- Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. These bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide.

Methanogenic- The methanogens convert the product of acetogenic step to methane and carbon dioxide. The produced gas consisting of methane, carbon dioxide, and traces of other ‘contaminant’ gases is known as biogas.

So, the correct answer is 'Hydrolytic $\rightarrow$ Acetogenic $\rightarrow$ Methanogenic'.

Multiple choice biology food production food production and microorganisms microbial products - food, medicines and industrial products uses of microorganisms

A number of organic compounds can be decomposed by

  1. Pseudomonas

  2. Mycoplasma

  3. Chemolithotrophs

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

Organic compounds like plant and animal residues are present in the soil. These organic compounds are broken down by a large number of bacteria, fungi, larger organisms. Bacteria like Pseudomonas lives in the soil and decomposes organic compounds and releases carbon dioxide, energy, water and other plant nutrients.

Thus, the correct answer is 'Pseudomonas.'

Multiple choice biology food production food production and microorganisms microbial products - food, medicines and industrial products uses of microorganisms

The most thoroughly studied of the known bacteria-plant interactions is the :-

  1. Gall formation on certain angiosperms by Agrobacterium

  2. Nodulation of Sesbania stems by nitrogen fixing bacteria

  3. Plant growth stimulation by phosphate solubilising bacteria

  4. Cyanobacterial symbiosis with some aquatic ferns
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Agrobacterium tumefaciens is called a natural plant genetic engineer. Using Agrobacterium vector, nematode specific genes were introduced into the host plant. The introduction was as such that it produced both sense and anti-sense RNA in the host cells. These two RNA's being complementary to each other formed a double-stranded (ds-RNA) that initiated RNAi and thus, silenced the specific mRNA of the nematode. The Agrobacterium is most widely studied of the known bacteria-plant interactions.
So the correct answer is 'Option A'.
Multiple choice biology food production food production and microorganisms microbial products - food, medicines and industrial products uses of microorganisms

Which is not a bacterial action?

  1. Nitrogen fixation

  2. Emulsification of fat

  3. Sewage disposal

  4. Ripening of cream
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • Nitrogen fixation is a process by which atmospheric nitrogen is converted into ammonium compounds and made available for plants. Examples include Rhizobium, Azotobacter.
  • Many bacteria are also involved in the sewage disposal process. Mostly saprophytic aerobic bacteria are used in treatment plants.
  • During the process of ripening of cream, Lactic acid bacteria are used. These bacteria convert lactose into acid and results in the curdling of cream.
Thus, the correct answer is 'Emulsification of fat.'

Multiple choice biology improvement in food resources crop yield improvement food supply crop improvement methods and organisations

A nitrogen fixing microbe associated with the fern Azolla in rice fields is:

  1. Frankia

  2. Rhizobium

  3. Spirulina

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

Anabaena azollae, a cyanobacterium that lives in symbiotic association with the free-floating water fern Azolla. Anabaena azollae can grow Photo-autotrophically and fixes atmospheric nitrogen. The inoculation of cyanobacteria in rice crops significantly influences the growth of rice crop by secretion of ammonia in floodwater.

Multiple choice biology anatomy of flowering plants theories of meristematic cell development theories of shoot apical meristem development shoot and root apex

Consider the following statements.
a. In the roots with endomycorrhizal association, the fungal hyphae penetrate the root cortex and pass through the casparian strip to enter vascular tissue.
b. The globin part of leghemoglobin in nitrogen-fixing root nodules is encoded by the bacterium whereas heme group is synthesized by the host plant.
Which of the statements given is/are correct?

  1. $1$ only
  2. $2$ only
  3. Both $1$ and $2$
  4. Neither $1$ nor $2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Reaction carried out by $N _2$ fixing microbes include
$2NH _3 + 3O _2 \rightarrow 2NO _2^- + 2H^+ + 2H _2O$            (i)
$2NO _2^- + O _2 \rightarrow 2NO _3^-$                                       (ii)
Which of the following statements about these equations is not true?

  1. Step (i) is carried out by Nitrosomonas or Nitrosococcus

  2. Step (ii) is carried out by Nitrobacter

  3. Both step (i) and (ii) can be called nitrification.

  4. Bacteria carrying out these steps are usually photoautotrophs.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Phototrophic bacteria are a group of bacteria, whose energy for growth is derived from sunlight and their source of carbon comes from carbon dioxide or organic carbon.
So, the correct option is 'Bacteria carrying out these steps are usually photoautotrophs'.
Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

A farmer adds Azotobacter culture to soil before sowing maize. Which mineral element will be replenished by doing so?

  1. N

  2. P

  3. K

  4. S
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Azotobacter is a free living bacteria in the soil. It helps some cereal crops like maize (Zea mays) in nitrogen fixation. The farmer adds Azotobacter culture to the maize field for enhancing the nitrogen element in the soil by the process of biological nitrogen-fixation. 
Thus, the correct answer is 'N.'

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which of the following is a non-symbiotic nitrogen fixing prokaryote?

  1. Azotobacter

  2. Clostridium

  3. Beijerinckia

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

Two kinds of nitrogen-fixing bacteria are recognized. The first kind, the free-living (non-symbiotic) bacteria, includes the cyanobacteria (or blue-green algae), Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium. 

Thus, the correct answers is 'All of these.'

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

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

  1. Nitrosomonas

  2. Rhizobium

  3. Azotobacter

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

Azotobacter and Beijerinckia  are aerobic free living saprophytic nitrogen fixing bacteria, while Clostridium is anaerobic free living saprotrophic nitrogen fixing bacterium.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which one of the following bacteria is not connected with nitrogen fixation?

  1. Azotobacter

  2. Nitrosomonas

  3. Frankia

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

Nitrogen fixation is referred to as conversion of atmospheric nitrogen into ammonia, whereas the Nitrosomonas is a genus of Gram-negative, chemoautotrophic bacteria. This organism oxidizes ammonia into nitrite as a metabolic process. 

 So, the correct option is 'Nitrosomonas'.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Which of the following is a flowering plant with nodules containing filamentous nitrogen-fixing microorganism?

  1. Cicer arietinum

  2. Casuarina equisetifolia

  3. Crotalaria juncea

  4. Cycas revolute
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Answer :
i) All the casuarinas are nitrogen-fixing. 
ii) Casuarinas support an actinorhiza symbiont in their root nodules, as opposes to the rhizobium symbiont found in the root nodules of leguminous trees that fix N2. 

Therefore correct answer is option B.Casuarina equisetifolia.

Multiple choice zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

Nitrifying bacteria convert the________________

  1. Nitrates into nitrites

  2. Ammonium salts into nitrates

  3. Ammonium salts into amino acids

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

Nitrifying bacteria are chemoautotrophic or chemolithotrophs depending on the genera (Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrococcus) bacteria that grow by consuming inorganic nitrogen compounds. Many species of nitrifying bacteria have complex internal membrane systems that are the location for key enzymes in nitrification: ammonia monooxygenase, which oxidizes ammonia to hydroxylamine, and nitrite oxidoreductase, which oxidizes nitrite to nitrate. Nitrifying bacteria are a narrow species in the environment and are found in the lowest numbers, where considerable amounts of ammonia are present (areas with extensive protein decomposition, and sewage treatment plants). Nitrifying bacteria thrive in lakes and rivers streams with high inputs and outputs of sewage and wastewater and freshwater because of the low ammonia content.