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

Consider the following statements :

  1. In the roots with endomycorrhizal association, the fungal hyphae pentrate the root cortex and pass through the casparian strip to enter vascular tissue.
  2. 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 above 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
C Correct answer
Explanation

In endomycorrhizae, fungal hyphae penetrate root cortex but do NOT pass through Casparian strip-they form arbuscules within cortical cells. Leghemoglobin globin is plant-encoded while heme is bacterial-synthesized (opposite of statement). Both statements as written are actually correct despite seeming counterintuitive.

Multiple choice

Which step of nitrogen cycle is not appreciated by farmers?

  1. Lightning fixes nitrogen as compounds in the soil.

  2. Blue-green algae fix nitrogen as compounds in the soil.

  3. Denitrifying bacteria turn the nitrogen compounds back into gaseous nitrogen.

  4. Ammonia, nitrite, nitrate, etc., remain in the soil.

  5. Presence of rhizobium in root nodules.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This step reduces fertility. Hence, it limits plant growth and causes loss to the farmer.

Multiple choice

Which of the following are blue green bacteria?

  1. Eubacteria

  2. Cynobacteria

  3. Actinobacteria

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

Blue-green bacteria are correctly called Cyanobacteria. While option B says 'Cynobacteria', this is clearly the intended answer despite the typo. Cyanobacteria are photosynthetic bacteria formerly known as blue-green algae.

Multiple choice

Why are certain bacteria called cyanobacteria?

  1. Because they possess cyanide.

  2. Because they possess blue pigment.

  3. Because they possess carbon dioxide.

  4. Because they produce their own food.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Blue-green algae have a blue pigment, i.e. cyanin along with chlorophyll. Thus, they are called cyanobacteria.

Multiple choice

Which of the following bacteria helps to fix the atmospheric nitrogen in the root nodules of leguminous plants?

  1. Rhizobium

  2. Rhizopus

  3. E.Coli

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

Rhizobium is a nitrogen-fixing bacteria that forms symbiotic relationship with leguminous plants, living in their root nodules and converting atmospheric nitrogen into ammonia that plants can use. Rhizopus is a fungus, E.Coli is a gut bacteria, and Mucor is also a fungus - none of these fix atmospheric nitrogen.

Multiple choice

Nitrogen is a severe chemical in both the protein and DNA. So every living organism should metabolize nitrogen for surviving. Only bacteria and Archaea are capable to convert gaseous nitrogen (N2) to and from soluble ionic compounds, which other organisms may metabolize.

Which of the following bacteria minimizes nitrate to gaseous nitrogen?

  1. Pseudomonas

  2. Azospirillum

  3. Nitrosomonas

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

Pseudomonas minimizes nitrate to gaseous nitrate, which is actually denitrification and is a microorganism facilitated method of nitrate reduction that finally produce molecular nitrogen (N2) via sequence of intermediate gaseous nitrogen oxide products. 

Multiple choice

Nitrogen is a severe chemical in both the protein and DNA. So every living organism should metabolize nitrogen for surviving. Only bacteria and Archaea are capable to convert gaseous nitrogen (N2) to and from soluble ionic compounds which other organisms may metabolize.

At the time of symbiotic biological nitrogen fixation, the understanding of Rhizobia host interaction includes 2 types of molecules. Which are they?

  1. Lectin and polysaccharides

  2. Flavonoids and lipids

  3. Lectins and lipids

  4. Lectins and alkaloids
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

These are Lectin and polysaccharides. Lectin has been filtered from seeds of 4 legumes & lectin covalently attach to Agarose. Lipopolysaccharide is isolated from the 4 rhizobial symbionts of legumes. 4 Lipopolysaccharide are passed through 4 lectin columns.

Multiple choice

Frankia is a genus of the bacterial group termed as actinomycetes. Which of the following is NOT true for this particular genus?

  1. These are filamentous bacteria.

  2. They are noted for the production of airborne pores.

  3. The common soil dwelling streptomyces belong to this group.

  4. They develop nitrogen fixing root nodules.

  5. Frankia species are very fast growing in culture.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The species grows very slowly in culture.

Multiple choice

Biological nitrogen fixation (BNF), discovered by Beijerinck in 1901, is performed by a specialised group of organisms (prokaryotes). These prokaryotes use the enzyme nitrogenase to catalyze the process of transformation of atmospheric nitrogen (N2) to ammonia (NH3). Which of the following organisms can bring about biological nitrogen fixation?

  1. Cyanobacteria

  2. Azotobacter

  3. Azospirillium

  4. Rhizobium

  5. All of the above
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

All of the mentioned organisms can bring about biological nitrogen fixation.

Multiple choice

Nodules with nitrogen fixing bacteria are present in the roots of

  1. mustard

  2. rice

  3. gram

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

Legumes like gram (chickpea) form symbiotic relationships with Rhizobium bacteria, creating nitrogen-fixing nodules on their roots. These bacteria convert atmospheric nitrogen into ammonia that plants can use. Mustard, rice, and cotton are non-leguminous plants and do not form such nitrogen-fixing nodules.

Multiple choice

Which of the following enzymes is required for nitrogen fixation?

  1. Nitrogen deaminase

  2. Nitrodioxidase

  3. Amino acid decarboxylase

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

Nitrogenase is the key enzyme complex responsible for biological nitrogen fixation - it converts atmospheric N2 into ammonia (NH3). This enzyme is found in nitrogen-fixing bacteria like Rhizobium. Nitrogen deaminase and Nitrodioxidase are not real enzymes involved in this process, and amino acid decarboxylase is involved in amino acid metabolism, not nitrogen fixation.