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 statements is/are not true about the nitrogen cycle? A. Biological nitrogen fixation amounts to more than 60% of the annual total fixation. B. Nitrogen fixation is achieved industrially by Haber Bosch process. C. Nitrification involves the reduction of nitrogen compounds. D. Decomposers carry out deamination resulting in the release of nitrogen. E. Nitrosomonas reduces ammonia to nitrites.

  1. A and B only

  2. B, C and E

  3. C, D and E

  4. D and E only
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 Nitrification involves oxidation of nitrogen compounds.  The decomposers carry out a process called deamination which results in the release of ammonia. Ammonia undergoes oxidation to give nitrates.

Multiple choice

The role of decomposers in nitrogen cycle is to

  1. fix N2 into ammonia

  2. release ammonia from organic compounds, thus returning it to the soil

  3. denitrify ammonia thus returning N2 into the soil

  4. incorporate nitrogen into amino acids and organic compounds
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Decomposers (bacteria and fungi) break down organic nitrogen compounds in dead organisms and waste products, releasing ammonia (NH3) into the soil through ammonification. This makes nitrogen available again for plants to use. Option A describes nitrogen fixation (by nitrogen-fixing bacteria), option C describes denitrification (by denitrifying bacteria), and option D describes assimilation (by plants, not decomposers).

Multiple choice

Which of the following is a pair of bacteria belonging to class Alphaproteobacteria?

  1. Brucella and Azospirillum

  2. Bordetella and Neisseria

  3. Chromatium and Legionella

  4. Desulfovibrio and Myxococcus

  5. Campylobacter and Helicobacter
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Brucella is a member of order Rhizobiales, class Alphaproteobacteria, phylum Proteobacteria. Azospirillum is a member of order Rhodospirillales, class Alphaproteobacteria, phylum Proteobacteria.

Multiple choice

Which of the following pairs is incorrectly matched?

  1. Moraxella : Anaerobic coccobacilli

  2. Neisseria : Aerobic, gram-negative cocci

  3. Francisella : Pleomorphic bacteria

  4. Pseudomonas : Aerobic, gram-negative rods

  5. Brucella : Non-motile coccobacilli
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Members of the genus Moraxella are strictly aerobic coccobacilli, i.e. intermediate in shape between cocci and rods.

Multiple choice

Which of the following bacteria is not an example of spirochetes?

  1. Treponema

  2. Spirillum

  3. Leptospira

  4. Borrelia

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An important morphological difference from the helical spirochetes is that Spirillum bacteria are motile by conventional polar flagella, rather than axial filaments. This is why Spirilum is not classified as spirochete.

Multiple choice

Which of the following is an example of gram-positive bacteria having ability to oxidise glucose by Entner–Doudoroff pathway?

  1. Bacillus subtilis

  2. Enterococcus faecalis

  3. Escherichia coli

  4. Xanthomonas campestris

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

Very few gram-positive bacteria have the ability to oxidise glucose by Entner–Doudoroff pathway. Enterococcus faecalis is an example of gram-positive bacteria having the ability to oxidise glucose by Entner–Doudoroff pathway.