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

A simple technology has been developed in India for plant breeders and farmers to use two plants as biofertilizers for growing rice. The two biofertilizers are

  1. azotobacter and rhizobium

  2. chlorella and spirulina

  3. azolla and nitrogen-fixing blue-green algae

  4. riccia and marchantia
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Azolla is a small water fern that forms symbiotic relationships with nitrogen-fixing cyanobacteria (Anabaena). Blue-green algae (cyanobacteria) are free-living nitrogen fixers. Together, these two biofertilizers are used in rice cultivation in India to reduce nitrogen fertilizer requirements. Azolla is grown in rice paddies and then incorporated into the soil. Neither azotobacter nor rhizobium are used in this system (rhizobium requires legume hosts).

Multiple choice

Rhodobacter belongs to which of the following nutritional groups?

  1. Photoorganoautotroph

  2. Photoorganoheterotroph

  3. Photolithoheterotroph

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

Rhodobacter is a photosynthetic bacterium. It uses photon energy for making food, organic oxidising donor source and organic carbon source. Thus, it is a photoorganoheterotroph.

Multiple choice

Which of the following is/are photoheterotroph(s)?

  1. Thermoacidophiles

  2. Green non-sulphur bacteria

  3. Kelp algae

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

Green non-sulphur bacteria are photoheterotrophs. They use light for energy and use organic compounds to satisfy their carbon needs.

Multiple choice

In the given paragraph, composition of a bacteriological medium is given. Which type of culture medium is it for the growth of Thiobacillus thiooxidans?

Component            Amount            Function

NH4Cl                     0.52 g              N source

KH2PO4                  0.28 g             P and K source

MgSO4 7H2O          0.25 g             S and Mg2+ source

CaCl2 2H2O            0.07 g             Ca++ source

Elemental Sulphur  1.56 g            Energy source

CO2                          5%                 C source  

Water                     1000 ml

pH 3.0

  1. Minimal medium

  2. Defined enrichment medium

  3. Complex medium

  4. Selective enrichment medium
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The above mentioned medium would act as a defined enrichment medium for the growth of Thiobacillus thiooxidans. It is chemically defined and it contains elemental sulphur as carbon source, enriching it for the growth of Thiobacillus thiooxidans.

Multiple choice

Which of the following bacteria are gram-positive and responsible for the peculiar odour emanating from the soil after rain (petrichor), mainly in warmer climates?

  1. Bacteroidetes

  2. Proteobacteria

  3. Actinobacteria

  4. Spirochetes

  5. Cyanobacteria
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Actinibacteria is gram-positive. It is responsible for the peculiar odour emanating from the soil after rain (petrichor), mainly in warmer climates. The chemical that produces this odour is known as geosmin.

Multiple choice

Which of the following bacteria are gram-negative, filamentous anoxygenic phototrophs, which use reduced sulphur compound for phototrophy, and also show 3-hydroxypropionate CO2 assimilatory pathway, with one of its species specially used for the study of evolution of photosynthesis?

  1. Firmicutes

  2. Chloroflexus

  3. Actinobacteria

  4. Mycoplamsas

  5. Cyanobacteria
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Choroflexus are gram-negative filamentous anoxygenic phototrophic (FAP) organism that do not produce oxygen as a byproduct of photosynthesis, in contrast to oxygenic phototrophs like cyanobacteria. It uses reduced sulphur compounds such as thiosulphate or elemental sulphur.

Instead of using the Calvin-Benson-Bassham Cycle typical of plants, Chloroflexus aurantiacus has been demonstrated to use a novel autotrophic pathway known as the 3-hydroxypropionate pathway.

Chloroflexus aurantiacus that can survive using either respiration or photosynthesis are of interest in on-going attempts to trace the evolution of photosynthesis.

Multiple choice

Which of the following bacteria are spirochetes?

  1. Mycobacterium leprae and Corynebacterium diphtheriae

  2. Neisseria gonorrhoeae and Escherichia coli

  3. Chlamydia trachomatis and Chlamydia psittaci

  4. Treponema pallidum and Borrelia burgdorferi

  5. Calothrix and Xenococcus
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Treponema pallidum and Borrelia burgdorferi are spirochetes.

Multiple choice

All of the following statements concerning the Actinomycetous filamentous soil bacterium Frankia are correct except that Frankia?

  1. forms specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids

  2. Can induce root nodules on many plant species.

  3. like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex

  4. Can fix nitrogen in the free-living state.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

  Frankia cannot fix nitrogen in the free-living state.Frankia is a nitrogen-fixing bacterium that lives in the soil and has a symbiotic relationship with many plants.

Multiple choice

Which of the following bacteria is comma shaped?

  1. Lactobacillus

  2. Streptococcus

  3. Vibrio

  4. Sarcina

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Vibrio bacteria are characterized by their distinctive comma or curved rod shape. Lactobacillus is rod-shaped, Streptococcus is spherical (cocci), and Sarcina forms cube-like clusters of 8 cells.