Biology ยท 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

Nitrogen gas is found in the atmosphere. How does it enter plants?

  1. Through gas exchange in plant leaves

  2. By a plant forming a symbiotic relationship with ants

  3. By being fixed by nitrifying bacteria

  4. By being fixed by denitrifying bacteria
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Plants cannot absorb nitrogen gas directly from the air. They rely on nitrogen-fixing bacteria, often in soil or root nodules, to convert nitrogen gas into a usable form like ammonia or nitrates.

Multiple choice

Which of the following is NOT involved in the nitrogen cycle?

  1. Bacteria

  2. Lightning

  3. Fertilizer

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

The nitrogen cycle involves biological processes (bacteria), atmospheric processes (lightning), and human inputs (fertilizer). Rocks are primarily associated with the phosphorus or rock cycles, not the nitrogen cycle.

Multiple choice

Microorganisms are mostly composed of

  1. C, H, O, N

  2. C and H

  3. C, H, O, N, S

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

The primary elements that make up the biomass of microorganisms (and all living things) are Carbon, Hydrogen, Oxygen, and Nitrogen.

Multiple choice

A stab culture would be one way to culture

  1. Staph

  2. an anaerobe

  3. a mesophile

  4. a halophile

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

A stab culture is used to test for motility or oxygen requirements. Anaerobes are often cultured in deep agar stabs to minimize exposure to atmospheric oxygen.

Multiple choice

A growth limiting nutrient for many microorganisms

  1. sulfur

  2. nitrogen

  3. oxygen

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

Nitrogen is a critical component of proteins and nucleic acids. Because it is often required in large amounts but is not always readily available in a usable form, it frequently acts as a limiting nutrient for microbial growth.

Multiple choice

Nitrifying bacteria are involved in ammonification

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ammonification is the process of converting organic nitrogen into ammonia, whereas nitrifying bacteria convert ammonia into nitrites and nitrates. They are distinct processes.

Multiple choice

Which bacteria acts as biofertilisers?

  1. Bacteria

  2. Parasites

  3. Chlamydomonas

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

Cyanobacteria (blue-green algae) are capable of fixing atmospheric nitrogen and are commonly used as biofertilizers in rice cultivation.

Multiple choice

Which of the following is the pair of biofertilisers?

  1. Azolla and blue green algae

  2. Nostoc and legume

  3. Rhizobium and grasses

  4. Salmonella & E. coli
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Azolla and blue-green algae (like Anabaena) are both widely used as biofertilizers in agriculture, particularly in rice cultivation.

Multiple choice

What's true about atmospheric nitrogen?

  1. It has the formula N3.

  2. It is useful for plants as they grow.

  3. It is the second most abundant atmospheric gas after oxygen.

  4. It has to be fixed by bacteria in order to be useful.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Atmospheric nitrogen (N2) is inert and cannot be used directly by plants. It must be 'fixed' by bacteria into forms like ammonia or nitrates to be biologically useful.

Multiple choice

What's the function of nitrogen-fixing bacteria?

  1. convert N2 into soil nitrogen

  2. convert carbon into nitrogen

  3. convert soil nitrogen into N2

  4. convert nitrate into nitrite
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into ammonia or other compounds in the soil that plants can absorb.