Biology

NIOS Biology Chapter 10 Nitrogen Metabolism

NIOS Class 12 Biology Intext Solutions Chapter 10

INTEXT QUESTIONS 10.1

1. What is the percent by volume of nitrogen gas in the atmosphere?

Ans: 78.03%

2. Name two biomolecules that contain nitrogen in plants.

Ans: Proteins and enzymes.

3. Why nitrogen is a stable molecule?

Ans: Molecular Nitrogen or diatomic nitrogen (N2) is highly stable as it is triple-bonded (N≡N).

4. What is the percentage of nitrogen in protein?

Ans: 16 percent.

5. What is the boiling point of nitrogen?

Ans: –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) atmospheric Nitrogen into → Ammonia

7. Nitrogen content of biosphere remains constant because of :

(a) Nitrogen cycle

(b) Nitrogen fixation

(d) Absorption of nitrogen

Ans: (a) Nitrogen cycle

8. Nitrates are converted into nitrogen by microbes called …..

Ans: Denitrifying Bacteria

INTEXT QUESTIONS 10.2

1. Define nitrogen fixation.

Ans: The conversion of molecular nitrogen into compounds of nitrogen, especially ammonia, is called nitrogen fixation. Nitrogen fixation is a reductive process, i.e., nitrogen fixation will stop if there is no reducing condition or if oxygen is present.

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 is the reduction of molecular nitrogen to ammonia by a living cell in the presence of enzymes called nitrogenases. In abiological nitrogen fixation, the nitrogen is reduced to ammonia without involving any living cell.

4. Name the enzyme that helps in nitrogen fixation in living cells.

Ans: Nitrogenase.

5. Which gas prevents nitrogen fixation?

Ans: Oxygen.

INTEXT QUESTIONS 10.3

1. Match the following:

Column A	Column 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 Ferredoxin

6. Match the following:

Column A	Column 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.

INTEXT QUESTIONS 10.4

1. Which is the most reduced form of inorganic nitrogen?

Ans: NH₄

2. Match the following:

Column A	Column B
(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, the reduction of nitrate to nitrite occur?

Ans: Cytosol

4 Which is the most oxidized form of inorganic nitrogen?

Ans: Nitrate

5 In which plant organelle reduction of nitrite to ammonia is catalyzed by the enzyme nitrite reductase?

Ans: Chloroplast.

INTEXT QUESTIONS 10.5

1. Match the following:

Column A	Column 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.