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

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

Which one of the following experiments suggests that simplest living organisms could not have originated spontaneously from non-living matter?

  1. Larvae could appear in decaying organic matter.

  2. Meat was not spoiled, when heated and kept sealed in a vessel.

  3. Microbes did not appear in stored meat.

  4. Microbes appeared from unsterilised organic matter.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  Meat was not spoiled, when heated and kept sealed in a vessel, This experiment suggests that simplest living organisms could not have originated spontaneously from non-living matter.This  experiment was showing evidence against theory of spontanous generation.

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.

Multiple choice

Which of the following is a nitrogen fixing bacterium?

  1. Rhozobium

  2. Acetobacter

  3. Mycoplasma

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

Rhizobium is a well-known nitrogen-fixing bacterium that forms symbiotic relationships with legume plants, converting atmospheric nitrogen into ammonia in root nodules. The question misspells it as 'Rhozobium', but this is clearly the intended answer. Acetobacter produces acetic acid, Mycoplasma lacks a cell wall, and Chlamydia is an intracellular pathogen - none fix nitrogen.

Multiple choice

Which of the following is a nitrogen fixing bacterium present in legume roots?

  1. Azotobacter

  2. Rhizobium

  3. Nitrobacter

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

Rhizobium forms a symbiotic relationship with legume roots, converting atmospheric nitrogen into ammonia through nitrogen fixation. This occurs in specialized root structures called nodules. Azotobacter is a free-living nitrogen fixer, while Nitrobacter and Nitrosomonas are involved in nitrification, not nitrogen fixation.

Multiple choice

Lithotrophs are categorized into different physiological groups based on their inorganic substrate for energy production and growth. Which of the following ‘physiological group: energy source’ pair are not correct?

  1. Hydrogen bacteria: H2
  2. Methanogens: CH4
  3. Carboxydobacteria: CO
  4. Iron bacteria: Fe+++

  1. 1 and 2 only

  2. 1 and 3 only

  3. 2 and 3 only

  4. 2 and 4 only

  5. 3 and 4 only
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The methanogens oxidizes H2 as a sole source of energy while transferring the electrons from H2 to CO2 in its reduction to methane. Iron bacteria oxidize Fe++ as energy source to Fe+++.