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

Which of the following pairs of bacteria shows positive Voges-Proskauer test?

  1. Enterobacter aerogenes and Escherichia coli

  2. Enterobacter aerogenes and Proteus mirabilis

  3. Escherichia coli and Klebsiella pneumoniae

  4. Escherichia coli and Proteus mirabilis

  5. Enterobacter aerogenes and Klebsiella pneumoniae
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Voges–Proskauer test is used to detect acetoin in bacterial broth culture. The test is performed by adding alpha-naphthol and potassium hydroxide to the Voges-Proskauer broth,  which has been inoculated with bacteria. A cherry red colour indicates a positive result, while a yellow-brown color indicates a negative result. Both Enterobacter aerogenes and Klebsiella pneumoniae give positive Voges–Proskauer test.

Multiple choice

Which of the following is the correct sequence of nodule formation after multiple interactions between Rhizobium and roots of the host plant?

(a) The infected root hair curls. (b) The nodule establishes a direct vascular connection with the host. (c) Bacteria gets modified into rod-shaped bacteroids. (d) Bacteria contacts a susceptible root hair and divide.

  1. c, a, d, b

  2. d, a, b, c

  3. b, a, c, d

  4. d, a, c, b

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

The correct sequence is d, a, c, b.

Multiple choice

What are the mutants that cannot grow on minimal medium and requires nutrient supplements called?

  1. Auxotrophs

  2. Prototrophs

  3. Heterotrophs

  4. Lithotrophs

  5. Methanotrophs
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Auxotrophs would be the mutant cells that are not capable of utilizing certain nutrients or synthesizing certain compounds. Auxotroph is a mutant that requires nutritive(s) not needed by the wild type (prototroph). Auxotrophic mutations have been extensively used for the study of biochemical pathways and for the identification enzymes catalyzing particular metabolic steps. In the example of bacteria capable of utilizing lactose as a nutrient source, the ability to lactose is denoted by lac+ and the inability to utilize lactose is denoted lac-.

Multiple choice

Match the columns:

 
Microbe its application
P. Thiobacterium ferrooxidans 1. Decomposition of DDT
Q. Aerobacter aerogenes 2. Biological leaching of uranium ores
R. Methylophilus methylotrophus 3. Curing of tea leaves
S. Mycococcus condisans 4. Production of single cell proteins

  1. P - 1, Q - 2, R - 3, S - 4

  2. P - 2, Q - 1, R - 4, S - 3

  3. P - 3, Q - 2, R - 1, S - 4

  4. P - 4, Q - 3, R - 2, S - 1

  5. P - 1, Q - 2, R - 4, S - 3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This option is correct.

Multiple choice

Which of these is NOT a process of nitrogen cycle occurring in nature?

  1. Starch is produced by photosynthesis

  2. Blue-green algae and bacteria fix nitrogen

  3. Uptake of nitrate by plants

  4. Lightning fixes nitrogen

  5. Death of organisms and nitrogenous waste excretion brings nitrogenous materials back to soil.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Photosynthesis is not a part of nitrogen cycle.

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.