Questions on Nitrogen Cycle
Multiple-Choice Questions: Nitrogen Cycle
1. What is the main reservoir of nitrogen in the nitrogen cycle?
A) Oceans
B) Plants
C) Atmosphere
D) Rocks
E) Animals
2. In what form is most nitrogen found in the atmosphere?
A) Nitrate (NO₃⁻)
B) Nitrite (NO₂⁻)
C) Ammonia (NH₃)
D) Nitrogen gas (N₂)
E) Nitric acid (HNO₃)
3. Which organisms can fix atmospheric nitrogen into a usable form?
A) Fungi
B) Viruses
C) Nitrogen-fixing bacteria
D) Insects
E) Protozoa
4. What is nitrogen fixation?
A) The absorption of nitrogen by rocks
B) The conversion of nitrates into nitrogen gas
C) The conversion of nitrogen gas into ammonia
D) The release of nitrogen from plants
E) The formation of acid rain
5. Legumes contribute to nitrogen fixation because they:
A) Absorb nitrogen gas through roots
B) Store nitrates in leaves
C) Form symbiotic relationships with nitrogen-fixing bacteria
D) Produce ammonia directly
E) Decompose quickly
6. What is ammonification?
A) Conversion of ammonia into nitrates
B) Conversion of dead organic matter into ammonia
C) Fixation of nitrogen by plants
D) Absorption of nitrogen by animals
E) Use of nitrates by fungi
7. Which process converts ammonia (NH₃) to nitrite (NO₂⁻) and then to nitrate (NO₃⁻)?
A) Nitrogen fixation
B) Ammonification
C) Nitrification
D) Denitrification
E) Photosynthesis
8. What is denitrification?
A) Absorption of nitrogen by plants
B) Conversion of nitrate to nitrogen gas
C) Conversion of ammonia to nitrite
D) Nitrogen fixation in animals
E) Storage of nitrogen in bones
9. Which of the following does not play a direct role in the nitrogen cycle?
A) Plants
B) Bacteria
C) Fungi
D) Lightning
E) Moonlight
10. How do animals obtain nitrogen?
A) Breathing nitrogen gas
B) Absorbing it through skin
C) Eating plants or other animals
D) Drinking nitrogen-rich water
E) Photosynthesis
11. Which human activity most disrupts the nitrogen cycle?
A) Using solar panels
B) Cutting down trees
C) Burning fossil fuels
D) Overusing nitrogen-based fertilizers
E) Mining for gold
12. Excess nitrogen in aquatic systems often causes:
A) Acid rain
B) Ozone depletion
C) Eutrophication
D) Greenhouse effect
E) Earthquakes
13. Which natural event can also fix atmospheric nitrogen?
A) Hurricanes
B) Earthquakes
C) Volcanic eruptions
D) Lightning
E) Snowstorms
14. Nitrifying bacteria are responsible for:
A) Denitrification
B) Ammonification
C) Nitrification
D) Nitrogen fixation
E) Photosynthesis
15. Why is nitrogen important for living organisms?
A) It is used for energy production
B) It builds DNA and proteins
C) It provides insulation
D) It helps break down food
E) It assists in photosynthesis
16. What is the role of decomposers in the nitrogen cycle?
A) Create nitrogen gas
B) Break down dead matter into ammonium
C) Absorb nitrogen gas from the air
D) Perform nitrification
E) Filter water
17. Nitrate (NO₃⁻) is mainly absorbed by:
A) Animals
B) Bacteria
C) Rocks
D) Plants
E) Fungi
18. Denitrification returns nitrogen to the atmosphere in the form of:
A) Ammonia
B) Nitrate
C) Nitrite
D) Nitrogen gas
E) Nitric oxide
19. An increase in nitrogen-containing fertilizers can lead to:
A) Increase in animal respiration
B) Reduced crop growth
C) Depletion of atmospheric oxygen
D) Water pollution and algal blooms
E) Global cooling
20. A key difference between the nitrogen and carbon cycles is:
A) The nitrogen cycle doesn’t involve bacteria
B) Nitrogen cannot be found in organic matter
C) Nitrogen needs to be fixed before it can be used
D) Carbon is found only in the atmosphere
E) Only nitrogen causes pollution
Answer Key with Explanations
1. C – Atmosphere
The atmosphere contains about 78% nitrogen, making it the largest reservoir.
2. D – Nitrogen gas (N₂)
Most atmospheric nitrogen is in the form of inert nitrogen gas (N₂).
3. C – Nitrogen-fixing bacteria
These bacteria convert N₂ into forms like ammonia that plants can use.
4. C – The conversion of nitrogen gas into ammonia
This process makes atmospheric nitrogen accessible to living organisms.
5. C – Form symbiotic relationships with nitrogen-fixing bacteria
Legumes host bacteria in their root nodules that fix nitrogen.
6. B – Conversion of dead organic matter into ammonia
Decomposers break down waste and dead organisms into ammonia.
7. C – Nitrification
Nitrifying bacteria convert ammonia first into nitrite, then into nitrate.
8. B – Conversion of nitrate to nitrogen gas
This process returns nitrogen to the atmosphere, completing the cycle.
9. E – Moonlight
Moonlight plays no role in the nitrogen cycle.
10. C – Eating plants or other animals
Animals consume nitrogen by ingesting organic matter.
11. D – Overusing nitrogen-based fertilizers
This leads to runoff and pollution of water systems.
12. C – Eutrophication
Excess nitrogen causes algal blooms that deplete oxygen in water.
13. D – Lightning
Lightning breaks atmospheric N₂ and helps form usable nitrogen compounds.
14. C – Nitrification
Nitrifying bacteria are key players in converting ammonia to nitrates.
15. B – It builds DNA and proteins
Nitrogen is a vital component of amino acids and nucleic acids.
16. B – Break down dead matter into ammonium
Decomposers release nitrogen back into the soil in ammonium form.
17. D – Plants
Plants absorb nitrates from the soil for growth and development.
18. D – Nitrogen gas
Denitrifying bacteria convert nitrate back into N₂ gas.
19. D – Water pollution and algal blooms
Runoff from fertilizers leads to nutrient-rich water and excessive algae.
20. C – Nitrogen needs to be fixed before it can be used
Unlike carbon, nitrogen gas must be converted into a usable form.
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