Nitrogen Metabolism : 12th Class Biology Question Answer Lesson 10 – NIOS

Nitrogen Metabolism : 12th Class Biology Question Answer Lesson 10 – NIOS

Nutrition in Plants – Mineral Nutrition : 12th Class Biology Question Answer Lesson 9 – NIOS


  1. What is the percent by volume of nitrogen gas in the atmosphere? – 78.03 percent
  2. Name two biomolecules that contain nitrogen in plants. – proteins and enzymes.
  3. Why nitrogen is a stable molecule? – Because it is triple bonded.
  4. What is the percentage of nitrogen in protein – 16 percent.
  5. What is the boiling point of nitrogen? – –195.8°C.
  6. Choose the correct option:
    Nitrogen fixation is the conversion of :
    (a) atmospheric Nitrogen ⎯⎯⎯into → Nitrates
    (b) atmospheric Nitrogen ⎯⎯⎯into → Ammonia
    (c) atmospheric Nitrogen ⎯⎯⎯into → Amino acids
    (d) both (a) and (b)
    Ans. b
  7. Nitrogen content of biosphere remains constant because of :
    (a) Nitrogen cycle
    (b) Nitrogen fixation
    (c) Industrial pollution
    (d) Absorption of nitrogen
    Ans. a
  8. Nitrates are converted into nitrogen by microbes called ..- Denitrifying Bacteria


  1. Define nitrogen fixation.
    Ans. Conversion of molecular nitrogen to ammonia.

  2. Which industrial process is utilized for converting nitrogen to ammonia?
    Ans. Haber’s process
  3. Distinguish between biological and abiological nitrogen fixation.
    Ans. Biological nitrogen fixation takes place in a living cell and abiological
    fixation without a living cell.
  4. Name the enzyme that helps in nitrogen fixation in living cells.
    Ans. Nitrogenase.
  5. Which gas prevents nitrogen fixation?
    Ans. Nitrogen


  1. Match the following:
    A B
    (i) Azotobacter (a) anaerobic nitrogen fixer.
    (ii) Clostridium (b) aerobic nitrogen fixer
    (iii) Lichens (c) aerobic nitrogen fixing cyanobacterium
    (iv) Anabaena (d) symbiotic nitrogen fixer.
    Ans. (i) b (ii) a (iii) d (iv) c
  2. Which Gymnospermous plant fixes nitrogen?
    Ans. Cycas
  3. Is there any other gas evovled during nitrogen fixation? If yes, name the gas evolved.
    Ans. Yes, Hydrogen gas.
  4. How many ATP molecules are required to reduce a single molecule of nitrogen?
    Ans. 16 ATP
  5. What is the major source of electrons for reduction of nitrogen?
    Ans. Reduced coenzymes such as Ferrodoxin
  6. Match the following:
    A B
    (i) Leghemoglobin (a) cyanobacterium
    (ii) Anabaena (b) Legumes
    (iii) Reductive process (c) nitrogen fixation
    Ans. (i) b (ii) a (iii) c
  7. Name the proteins that help in establishing symbiosis and maintain root nodule functioning in legumes.
    Ans. Nodulins.


  1. Which is the most reduced form of inorganic nitrogen – NH4
  2. Match the following:
    (i) Nitrate reductase (a) nitrogen fixation
    (ii) Nitrite reductase b) nitrate reduction
    (iii) Nitrogenase c) nitrite reduction
    Ans. (i) b (ii) c (iii) a
  3. In which part of the cell, reduction of nitrate to nitrite occurs?
    Ans. Cytosol.
  4. Which is the most oxidized form of inorganic nitrogen? – Nitrate
  5. In which plant organelle reduction of nitrite to ammonia is catlyzed by the enzyme nitrite reductase? – Chloroplast


  1. Match the following:
    A B
    (i) Amino acid (a) keto acid
    (ii) Glutamic acid (b) amino group and carboxyl group
    (iii) α-ketoglutaric acid (c) amino acid
    Ans. (i) b (ii) c (iii) a
  2. Name two biochemical reactions for biosynthesis of amino acids in plants.
    Ans. Reductive amination and transamination.
  3. Which group of enzymes catalyzes transamination reaction?
    Ans. Transaminases.
  4. What is the source of amino group for amino acid synthesis in reductive
    amination reaction?
    Ans. Ammonia
  5. Which keto acid is the source for synthesis of glutamic acid?
    Ans. Alpha ketoglutaric acid.


  1. Define nitrogen fixation.
  2. Which form of combined nitrogen may be formed during lightening storms?
  3. Name three biomolecules other than enzymes and proteins, which contain
  4. Name one aerobic and one anaerobic bacterium, which fixes nitrogen.
  5. Which amino acid is synthesized due to reductive amination of α-ketoglutaric
  6. Differentiate between biological and abiological nitrogen fixation.
  7. What is required for biological nitrogen fixation?
  8. How does human hemoglobin differ from leghemoglobin?
  9. What is the function of leghemoglobin?
  10. What are the functional differences between nitrate reductase and nitrite
  11. What is the difference between nitrogen fixation and nitrogen assimilation?
    Describe in brief the process of abiological nitrogen fixation.
  12. Describe in brief various steps involved in biological nitrogen fixation.
  13. Enumerate various free living and symbiotic nitrogen fixing systems with suitable
  14. What are the major differences between free living and leguminous nitrogen
    fixing organisms?
  15. Describe in brief nitrate and nitrite reduction in plants..
  16. Describe in brief the reductive amination reactions for synthesis of amino acids
    in plants.
  17. Describe the transamination reaction for synthesis of amino acids in plants. How
    does this differ from reductive amination?

NIOS 12th class biology Q Ans

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