MCQs on Nitrogen Metabolism & Fixation for ICAR (SRF or JRF) /ASRB /CSIR NET/BET Exams #1

 

1. The conversion of nitrogen to ammonia or nitrogenous compounds is called:
   (A) Nitrogen assimilation
   (B) Nitrogen fixation
   (C) Denitrification
   (D) Nitrification

2. Plants absorb N₂ in the form of:
   (A) Nitrites (NO₂⁻)
   (B) Nitrates (NO₃⁻)
   (C) Ammonium (NH₄⁺)
   (D) All of the above

3. Plants cannot absorb molecular N₂ in the atmosphere because:
   (A) N₂ has double bonds making it highly stable
   (B) Abundance in the atmosphere inhibits absorption
   (C) N₂ has triple bonds making it highly stable
   (D) None of these

4. Symbiotic N₂ fixing cyanobacteria are present in all except:
   (A) Anthoceros
   (B) Azolla
   (C) Cycas
   (D) Gnetum

5. All the following are free-living N₂ fixers except:
   (A) Rhizobium
   (B) Azotobacter
   (C) Rhodospirillum
   (D) Clostridium

6. Which of the following N₂ fixers is involved in symbiotic association with legumes forming root nodules?
   (A) Rhizobium
   (B) Azotobacter
   (C) Rhodospirillum
   (D) Clostridium

7. Anabaena, a N₂ fixer, is present in the root pockets of:
   (A) Marselia
   (B) Salvinia
   (C) Pistia
   (D) Azolla

8. Splitting of dinitrogen molecule into free nitrogen atoms in biological N₂ fixation is carried out by:
   (A) Hydrogenase
   (B) Nitrogenase
   (C) Dinitrogenase
   (D) Nitrate reductase

9. The conversion of amino acids to ammonium by soil decomposers is called:
   (A) Ammonification
   (B) Mineralization
   (C) Deamination
   (D) Both A and B

10. Industrial nitrogen fixation is accomplished by:
    (A) Helmonts process
    (B) Haber process
    (C) Friedel-Crafts reaction
    (D) Reimer-Tiemann reaction

11. To fix one molecule of nitrogen:
    (A) 6 ATP molecules are required
    (B) 12 ATP molecules are required
    (C) 16 ATP molecules are required
    (D) 20 ATP molecules are required

12. The root nodules of legumes contain a pink pigment with high affinity for oxygen, called:
    (A) Nod haemoglobin
    (B) Leghaemoglobin
    (C) Haemoglobin
    (D) Bacterial haemoglobin

13. Conversion of NO₂⁻ to NO₃⁻ is carried out by:
    (A) Nitrosomonas
    (B) Nitrosococcus
    (C) Nitrobacter
    (D) Clostridium

14. The process of conversion of soil NO₃⁻ to N₂ is called:
    (A) Nitrification
    (B) Denitrification
    (C) Ammonification
    (D) Nitrogen fixation

15. Leghaemoglobin creates:
    (A) Anaerobic condition for optimum activity of nitrogenase
    (B) Aerobic condition for optimum activity of nitrogenase
    (C) Required oxygen concentration for optimum activity of nitrogenase
    (D) Suitable environment for nodule formation