Nitrogen Fixation MCQ with Answers: 

1. Nitrogen is absorbed by plants as _____.

A. Nitrites

B. Ammonium

C. Nitrites

D. All of the above

Answer: D

2. What is the first stable product of nitrogen fixation in the root nodules of leguminous plants?

A. Glutamate

B. NO3–

C. Ammonia

D. NO2–

Answer: C

3. Which enzyme is involved in nitrogen fixation?

A. Nitrogenases

B. Isomerase

C. Denitrogenase

D. Methyl Transferase

Answer: A

4. Which of the following statements about nitrogen-fixing bacteria is incorrect__________

A. A rhizobia can invade all species of legumes

B. Mutual symbiosis between legumes and the rhizobia in their nodules

C. The rhizobia in the soil cannot fix nitrogen

D. Legumes with root nodules can use nitrogen as a nitrogen source

Answer: A

5. Which crop is helpful in nitrogen fixation?

A. beans, 

B. peanuts

C. soy

D. All of these 

Answer: D

6. Leghaemoglobin is present in the root nodules of legumes. What is the function of leghaemoglobin?

A. Oxygen removal

B. Inhibition of nitrogenase activity

C. Expression of nif gene

D. Nodule differentiation

Answer: A

7. Which of the following is nitrogen fixing bacteria?

A. Rhizobium trifolii

B. Clostridium pasteurianum

C. Azotobacter sp.

D. Escherichia coli

Answer: A

8. What is true about biological nitrogen fixation?

A. Nitrogen-fixing microorganisms reduce nitrogen in the air to ammonia

B. Legumes are capable of biological nitrogen fixation

C. Autogenic nitrogen-fixing microorganisms are autotrophs

D. The energy source of symbiotic nitrogen-fixing microorganisms is light energy

Answer: A

9. Which of the following is correct for nitrifying bacteria?

A. They convert free nitrogen to nitrogen compounds

B. They oxidize ammonia to nitrates

C. They reduce nitrates to free nitrogen

D. They convert proteins into ammonia

Answer: B

10. Rhizobium is a nitrogen-fixing microorganism, one of its biological characteristics is_________

A. Able to fix nitrogen when living independently in the soil

B. Aerobic heterotrophic bacteria

C. The energy required is provided by its own mitochondria

D. unicellular eukaryotes

Answer: B

11. Self- and symbiotic nitrogen-fixing microorganisms can______

A. Atmospheric N 2 is converted to NH 3

B. Atmospheric N 2 is converted to NO 3 –

C. NH 3 in soil is converted to NO 3 –

D. NO3 in soil – converted to N2

Answer: A

12. Splitting of dinitrogen molecule into free nitrogen atom in biological N2 fixation is carried out by _____

A. Nitrogenase

B. Amylase

C. Protease

D. Methyl Transferase

Answer: A

13. Which of the following statements about rhizobia is correct?

A. Rhizobium can also fix nitrogen outside plant roots

B. Rhizobium cannot survive without the root of the plant

C. When the soil is flooded, nitrogen fixation by rhizobia decreases

D. The nitrogen required for the growth of soybean plants comes from the rhizobia

Answer: C

14. How many ATP are required for nitrogen fixation?

A. Microbes fixing nitrogen need 16 moles of ATP for the reduction of each mole of nitrogen. 

B. Microbes fixing nitrogen need 32 moles of ATP for the reduction of each mole of nitrogen. 

C. Microbes fixing nitrogen need 8 moles of ATP for the reduction of each mole of nitrogen. 

D. Microbes fixing nitrogen need 24 moles of ATP for the reduction of each mole of nitrogen. 

Answer: A

15. Which of the following statements about root nodules and rhizobia is correct__________

A. The genes that control nitrogen fixation traits are located on nucleoid DNA molecules

B. Rhizobium can survive in soil but cannot fix nitrogen

C. A rhizobia can only invade one type of legume

D. The shape of root nodules is determined by the genes of legumes

Answer: B

16. Which of the following statements about biological nitrogen fixation is incorrect__________

A. Some bacteria, actinomycetes, cyanobacteria, etc. can carry out biological nitrogen fixation, and their cells have no nuclear membrane

B. Azotobacter rotundus can not only fix nitrogen, but also promote plant growth and fruit ripening

C. Rhizobium can provide the fixed N element to legumes in the form of NH 3

D. The metabolic type of Rhizobium is heterotrophic and aerobic, and its nitrogen-fixing gene has no exons and introns

Answer: B

17. The mutually beneficial symbiotic relationship between legumes and rhizobia is mainly reflected in__________

A. Legumes obtain nitrogen-containing inorganic substances from rhizobia, and rhizobia obtain carbohydrates from legumes

B. Legumes obtain nitrogen-containing organic matter from rhizobia, and rhizobia obtain nitrogen-containing inorganic matter from legumes

C. Legumes obtain N 2 from rhizobia , and rhizobia obtain organic matter from legumes

D. Legumes obtain NO 3 − from rhizobia, and rhizobia obtain NH 3 from legumes .

Answer: A

18. Which of the following statements about the nitrogen cycle is false_________

A. Nitrogen in soil is finally converted into nitrate by nitrifying bacteria under aerobic conditions

B. Denitrifying bacteria in soil convert nitrate to nitrite and finally nitrogen gas under anoxic conditions

C. Plants can only use nitrate in the soil, but cannot directly use nitrogen in the air

D. The metabolic type of autotrophic nitrogen-fixing bacteria belongs to autotrophic aerobic type

Answer: D