Nitrogen Cycle Multiple Choice Questions MCQs with Answers

1. The largest reservoir of nitrogen is…?
a. Soil
b. Water
c. Air
d. Rocks
Answer: c. Air

2. How much of the atmosphere is made up of nitrogen?
a. 21%
b. 78%
c. 80%
d. 50%
Answer: b. 78%

3. In living organisms, nitrogen is present in form of:
a. Element
b. Free
c. Combined
d. Amino acids
Answer: d. Amino acids

4. A completely free-living organism which takes part in nitrogen fixation is:
a. Anabaena
b. Bacillus
c. Rhizobium
d. Azotobacter
Answer: d. Azotobacter

5. Nitrogen is one of the essential constituents of all living organisms as part of:
a. Proteins
b. Chlorophyll
c. Nucleic acids
d. All of these
Answer: d. All of these

6. How many principal stages of the nitrogen cycle are there?
a. Two
b. Three
c. Four
d. Five
Answer: b. Three

7. Which of the following processes results in the decrease of nitrogen content in soil?
a. Denitrification
b. Ammonification
c. Biological nitrogen fixation
d. Nitrification
Answer: a. Denitrification

Recommended: Nitrogen Cycle Practice Test

8. Decomposition of organic nitrogen of dead plants and animals into ammonia is known as:
a. Denitrification
b. Ammonification
c. N2 fixation
d. Nitrification
Answer: b. Ammonification

9. Which of the following is released by micro-organisms?
a. Amino acids
b. Ammonia
c. Nitrates
d. Nitrites
Answer: b. Ammonia

10. Ammonification in the nitrogen cycle is brought about by the activity of:
a. Pseudomonas
b. Nitrosomonas
c. Rhizobium
d. Nitrobacter
Answer: c. Rhizobium

11. Several bacteria in soil oxidize ammonia or ammonium ion this is known as:
a. Nitrification
b. assimilation
c. all of mentioned above
d. Ammonification
Answer: a. Nitrification

12. Plants can utilize nitrogen in the form of?
a. Nitrites
b. Nitrates
c. NH4+
d. All of these
Answer: d. All of these

13. The two ions which are formed when ammonia dissolves in water are ammonium ion and…?
a. OH-
b. H3O+
c. H+
d. O-2
Answer: a. OH-

14. Nitrogen fixation is the conversion of…?
a. N2 to N
b. N2 to NH3
c. N2 to NO3–
d. N2 to urea
Answer: b. N2 to NH3

15. Which of the following enzymes are involved in nitrogen fixation?
a. Nitrogenase and hydrogenase
b. Nitrogenase and hexokinase
c. Nitrogenase and hydrolyse
d. Nitrogenase and peptidase
Answer: a. Nitrogenase and hydrogenase

16. In which of the following symbiotic nitrogen-fixing cyanobacteria are not present?
a. Azolla
b. Anthoceros
c. Cycas
d. Gnetum
Answer: d. Gnetum

17. During symbiotic nitrogen fixation; how many ATPs are used in fixing one mole of Nitrogen?
a. 18
b. 10
c. 20
d. 16
Answer: d. 16

18. The conversion of nitrates to nitrogen gas by bacteria is known as:
a. Denitrification
b. Ammonification
c. N2 fixation
d. Nitrification
Answer: a. Denitrification

19. The conversion of ammonia into nitrites and nitrates is known as:
a. Denitrification
b. Ammonification
c. Nitrification
d. None of these
Answer: c. Nitrification

20. Conversion of nitrate to ammonia is a…?
a. Amination process
b. Deamination process
c. Oxidative process
d. Reductive process
Answer: d. Reductive process

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