WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Nitrogen Cycle

Chapter 5 Nitrogen Cycle Summary

WBBSE Class 10 Nitrogen Cycle Overview

• Our environment is composed of both living and non-living things. Nitrogen is an important element for organisms. 78.09% of the air is nitrogen. Nitrogen, like other elements, also moves through biotic and abiotic components of the ecosystem, which is known as the nitrogen cycle or N₂ cycle.
• The main stages of the nitrogen cycle are-biological and non-biological fixation of nitrogen from the atmosphere, entry of nitrogen into the organism from the soil, and re-entry of nitrogen into the soil through ammonification, nitrification, and denitrification or release of N₂ into the air.
• The conversion of atmospheric nitrogen into a nitrogenous compound is called nitrogen fixation. The atmospheric nitrogen is fixed by several prokaryotes, i.e. some soil bacteria (Azotobacter and Clostridium), some cyanobacteria (Nostoc, Anabaena), and some symbiotic bacteria (Rhizobium).
• Also, atmospheric nitrogen is converted into nitrous oxide by the electrical energy of lightning, which is brought down by rain and is used by plants.

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• Ammonifying bacteria like Bacillus mycoides convert excretory substances of organisms and dead organic matter into ammonia. Nitrifying bacteria like Nitrosomonas convert ammonia, into nitrate and nitrite called nitrification.
• Finally, nitrate and nitrite is converted into N₂ and released into the atmosphere by denitrifying bacteria like Pseudomonas, and Thiobacillus. Human activities, such as the use of fertilizers greatly increase the amount of nitrogen that is cycling between the living world and soil, water, and atmosphere.
• This results in increased global concentrations of N₂O, which causes global warming, and substantial acidification of water bodies and soil.

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Chapter 5 Nitrogen Cycle Long Answer Type Questions

Question 1. Describe the nitrogen cycle with the help of a flowchart. Similar question, Show the steps of the nitrogen cycle with the help of a flow chart. Part question, Analyse the role of bacteria at any three steps of the nitrogen cycle.

Answer:

Nitrogen cycle:

The nitrogen cycle is a bio-geochemical process which involves different phases, which are-nitrogen fixation in soil, entry of nitrogen from soil into living organisms, return of nitrogen from organisms to soil, and liberation of nitrogen in the atmosphere. The phases are explained in the next section.

1. Nitrogen fixation:

By this process, atmospheric nitrogen is trapped in the soil. This occurs by three different processes, which are-

Natural N₂ fixation:

During lightning, a huge amount of heat is generated in the atmosphere, when nitrogen and oxygen react gradually to produce nitric oxide (NO) and nitrogen dioxide (NO₂).

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When rainwater mixes with atmospheric nitrogen dioxide two acids, namely nitrous acid (HNO₂) and nitric acid (HNO₃) are produced. The reactions are given below-

N₂+O₂ → 2NO,  2NO+O₂ → 2NO₂, 2NO₂ + H₂O → HNO₂ + HNO₃

These two acids then react with the minerals present in soil and form nitrates (potassium nitrate, calcium nitrate, etc.).

Biological fixation:

Biological nitrogen fixation is done in the following ways-

1. Soil-dwelling nitrifying bacteria like Azotobacter sp., Clostridium sp., etc. absorb atmospheric nitrogen and trap it in their cells. When these bacteria die, the nitrogenous compounds mix in the soil.
2. Cyanobacteria like Anabaena sp. and Nostoc sp. absorb nitrogen from the atmosphere and add it to the soil.
3. Rhizobium sp. present in root nodules of leguminous plants traps atmospheric nitrogen and converts it into nitrogenous compounds. With the death of the host plants, these compounds mix in the soil to increase its nitrogen content.

Industrial fixation:

In fertilizer industries, different nitrogen-rich fertilizers are produced. By the Haber-Bosch method, N₂ and H₂ are made to react at 300-400°C under 35-100 MPa (Mega Pascal) pressure to produce NH₃.

This NH₃ and other nitrogen-rich fertilisers when added to soil increases the nitrogen content.

2. Entry of nitrogen from soil into living organisms:

Plants absorb soluble nitrogenous salts from the soil through their roots. This nitrogen takes part in synthesizing plant proteins. Animals get nitrogen either directly or indirectly by consuming plants.

Finally, plant proteins are transformed into animal proteins and remain in the animal bodies.

3. Return of nitrogen from organisms to soil:

Nitrogen returns from the body of organisms to the soil through two different steps. These are-

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Ammonification:

The ammonifying bacteria (Bacillus mycoides, Micrococcus sp., etc.) act upon dead animal and plant bodies and the excretory materials to convert the nitrogenous compounds in it into ammonia. This is called ammonification.

Nitrification:

Certain nitrifying bacteria convert ammonia into nitrates through two steps of reaction.

1. Nitritation-In the first step, Nitrosomonas sp. converts ammonia and ammonium ions into nitrites.
2. Nitratation-In the next step, soil-dwelling Nitrobacter sp. transforms nitrites into nitrates.

2NH₄⁺+3O₂ → 2NO₂^–+ 4H⁺ + 2H₂O,   2NO₂^–+O₂ → 2NO₃

4. Liberation of nitrogen into the atmosphere or denitrification:

In this phase, several bacteria act upon nitrites and nitrates in the soil and liberate free nitrogen into the atmosphere. This biochemical process is called denitrification. Pseudomonas sp., Thiobacillus sp., etc. are a few bacterial species, which help in denitrification.

2NO₃^–  → 2NO₂^–, → NO + N₂O → N₂

Stages of the Nitrogen Cycle Explained

Question 2. ‘Nitrogen cycle is affected due to human activities’-State two phenomena to justify it. Explain the adverse effects of excess nitrogen in the atmosphere, liberated due to human activity. Similar question, Explain any three incidences which are occurring as a result of the disruption of the nitrogen cycle.

Answer:

Human actions affecting the nitrogen cycle:

The human actions affecting the nitrogen cycle are discussed below.

1. Application of nitrogen-rich fertilizers:

Nowadays, farmers apply an excess amount of nitrogen-rich fertilizers in crop fields to increase productivity. Due to this practice, the content of N₂O and NO₂ is rising alarmingly in the atmosphere.

2. Cultivation of nitrogen-fixing plants:

Leguminous plants like gram, peas, lentils, soya beans, etc. are important sources of plant protein. To fulfill the need of protein, different pulses are being cultivated more and more. These plants efficiently absorb nitrogen from the atmosphere and trap it in the soil.

3. Burning of fossil fuel:

Excessive burning of fossil fuels such as mineral oils, coal, etc. increases nitric oxide (NO), nitrous oxide (N₂O), and nitrogen dioxide (NO₂) in the air. It increases the supply of nitrogen in the environment.

Adverse effects of excess nitrogen in the atmosphere due to human activity:

The adverse effects of excess nitrogen in the atmosphere, due to human activity, are mentioned below.

1. Global warming:

Nitrous oxide (N₂O) is a potent greenhouse gas. Accumulation of this gas in air arrests more heat in the atmosphere and causes global warming.

2. Acid rain:

Oxides of nitrogen present in the atmosphere mix with rainwater to produce nitrous and nitric acids. These acids come down on earth as acid rain, which acidifies soil and water bodies to cause serious environmental pollution.

3. Photochemical smog:

Nitric oxide (NO), released as automobile exhaust, reacts with atmospheric hydrocarbons in the presence of sunlight. This reaction produces a polluting gas, named PAN (Peroxy-acetyl nitrate).

It mixes with smoke and creates a very harmful photochemical smog. This reduces visibility through air, and causes inflammation of the respiratory tract and various other respiratory diseases.

Question 3. Explain the microbial fixation of atmospheric nitrogen in the nitrogen cycle.

Answer:

Microbial fixation of atmospheric nitrogen in the nitrogen cycle:

Certain microorganisms are capable of absorbing atmospheric nitrogen and trapping it in soil. This mechanism of trapping of atmospheric nitrogen with the help of microorganisms is called biological nitrogen fixation. Two types of microorganisms take part in this process, which are described here.

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1. Nitrogen fixation by free-living microbes:

Few free-living soil-dwelling bacteria like Clostridium sp., Azotobacter sp., and few cyanobacteria like Anabaena sp. (a symbiont with Azolla as well), Nostoc sp., etc. absorb atmospheric nitrogen and convert it into nitrogenous compounds within their cell.

As the microbes die these nitrogenous compounds mix in the soil to increase its nitrogen content.

2. Nitrogen fixation by symbiotic microbes:

Rhizobium sp. is a soil-dwelling bacterium, which enters into the root tissues of leguminous plants and stays there as a symbiont. As the bacterium enters in to the host tissue, the root cells start to divide quickly to form nodules.

Rhizobium, inhabiting in these root nodules, absorbs atmospheric nitrogen and converts it into various nitrogenous compounds. A portion of these nitrogenous compounds is supplied to the host plant and the rest is stored in the microbial cell body.

When these plants die and are decomposed, these nitrogenous compounds get mixed in soil, to increase the fertility of the soil.’

Chapter 5 Nitrogen Cycle Short Answer Type Questions

Question 1. What is meant by the bio-geochemical cycle?
Answer:

Bio-geochemical cycle:

The continuous cycling of different elements (C, H, N, O, P, S, Ca, etc.) among biotic and abiotic components of the environment is called a bio- geochemical cycle. The nitrogen cycle is an important biogeochemical cycle in the environment.

Question 2. What will happen if the bio-geochemical cycle is disrupted?
Answer:

The bio-geochemical cycle is disrupted:

If the bio-geochemical cycle is disrupted, the balance of the important elements in the environment would have been disturbed. This may lead to natural disasters.

Question 3. Why deficiency of basic elements does not occur in the environment?
Answer:

Deficiency of basic elements does not occur in the environment

Deficiency of basic elements never occurs in the environment, because living organisms never uptake any element permanently from the environment. The organisms release such elements as compounds through excretion.

Alternatively, these are liberated in the environment by the decomposition of the dead and.. decaying organic matter.

Question 4. What is the nitrogen cycle?
Answer:

Nitrogen cycle:

The nitrogen cycle is a bio-geochemical cycle, which describes how nitrogen circulates in the atmosphere, the soil, and living organisms. So, by the help of this biogeochemical cycle, the content of nitrogen in atmosphère and in living organisms remains unaltered.

Question 5. Mention the importance of nitrogen in living organisms.
Answer:

The importance of nitrogen in living organisms:

The main structural component of a living body is protein. Nitrogen, on the other hand, is the main structural element of protein. That is why, nitrogen is important for all living organisms.

Importance of Nitrogen Cycle in Ecosystems

Question 6. What is meant by nitrogen fixation?
Answer:

Nitrogen fixation:

Atmospheric nitrogen is trapped in to the soil in the form of different nitrogenous compounds by a number of physicochemical or biochemical processes. These processes are collectively known as nitrogen fixation.

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Question 7. What is meant by biological nitrogen fixation?
Answer:

Biological nitrogen fixation:

Certain blue-green algae or cyanobacteria and a few bacteria absorb nitrogen directly from the atmosphere and reduce it to ammonia with the help of an enzyme, nitrogenase.

This ammonia then assimilates in the protoplasm of these microbial organisms. This biochemical trapping of atmospheric nitrogen is called biological nitrogen fixation.

Question 8. What is formed by the reaction between atmospheric nitrogen and oxygen during lightning?
Answer:

During lightning, a large amount of heat is generated in the sky, when nitrogen and oxygen react gradually to produce nitric oxide (NO) and nitrogen dioxide (NO₂). The reactions are given below.

N₂+O₂ → 2NO,  2NO+O₂ →2NO₂

Question 9. What happens when rainwater mixes with atmospheric nitrogen dioxide?
Answer:

When rainwater mixes with atmospheric nitrogen dioxide two acids, namely nitrous acid (HNO,) and nitric acid (HNO₃) are formed. The reaction is mentioned below.

2NO₂ + H₂O→ HNO₂ + HNO₃

Question 10. What is ammonification?
Answer:

Ammonification:

The biochemical process, by which dead animal and plant bodies or nitrogenous waste matters are acted upon by certain bacteria to produce ammonia, is known as ammonification. Bacillus mycoides, Micrococcus sp., etc. are a few examples of ammonifying bacteria.

Question 11. What is nitrification?
Answer:

Nitrification:

The biochemical process, by which soil ammonia is first converted into nitrite and finally into nitrate, is known as nitrification. Nitrosomonas, Nitrobacter, etc. are a few examples of nitrifying bacteria that help in this process.

Question 12. What is denitrification?
Answer:

Denitrification:

The biochemical process, by which nitrate or any other nitrogenous compounds break to liberate free nitrogen into the atmosphere, is known as denitrification. Certain bacteria like Thiobacillus, Pseudomonas, etc. are denitrifying in nature.

Question 13. Mention the role of bacteria in the nitrogen cycle.
Answer:

The role of bacteria in the nitrogen cycle are as follows-

1. Certain bacteria trap atmospheric nitrogen and reduce it to form ammonia.
2. A few others, then convert this ammonia into nitrite.
3. Certain other bacteria, then transform nitrite into nitrate.
4. A few other bacteria break nitrates to liberate elementary nitrogen into the atmosphere.

Question 14. Mention the role of bacteria in nitrification.
Answer:

The role of bacteria in nitrification:

Bacteria like Bacillus mycoides, Micrococcus sp., etc. reduce nitrogen from decomposing organic matter to produce ammonia. Nitrosomonas sp. then converts the ammonia into nitrites.

Nitrobacter sp. acts upon these nitrites and oxidizes them to stable nitrates. This is how bacteria help in nitrification.

Nitrogen Fixation Process in Detail

Question 15. Mention the importance of soil-living microbes.
Answer:

The importance of soil-living microbes:

Soil-living microbes help in the decomposition of dead organisms and other organic matter. By this process, several simple organic compounds and elements mix in the soil to prepare hummus. This humus gradually increases nutrients in the soil and makes it more fertile.

Question 16. Mention the role of bacteria in increasing soil fertility.
Answer:

The role of bacteria in increasing soil fertility:

Free-living soil bacteria like Azotobacter, Clostridium, etc., and symbiotic bacteria like Rhizobium absorb atmospheric nitrogen and trap it in the form of nitrogenous compounds.

These compounds increase the nitrogen content in the soil, thus, increasing soil fertility.

Question 17. Write the names of two microorganisms participating in the process of biological nitrogen fixation.
Answer:

The two microorganisms participating in the process of biological nitrogen fixation are- Azotobacter (free-living) and Rhizobium (symbiotic).

Question 18. What is hummus?
Answer:

Hummus:

After the death of animals and plants, the bodies are decomposed and various organic matters mix in the soil. This brownish, sticky organic matter, which is generally acidic in nature, is known as humus.

Word Problems on Nitrogen Cycle for Class 10

Question 19. What is leghaemoglobin?
Answer:

Leghaemoglobin:

Leghaemoglobin is a pinkish-red pigment present in the nitrogen-absorbing root nodules of leguminous plants. The structure of this pigment and its capacity of absorbing oxygen is similar to that of hemoglobin.

This pigment is present in the space between the symbiotic bacterial cell and the surrounding host cells.

Question 20. Why do the leaves of insectivorous plants have different modifications?
Answer:

Insectivorous plants grow in such soil, where nitrogen content is significantly low. To compensate for the short supply of nitrogen, these plants trap insects and digest them to absorb protein from their body.

To trap insect prey efficiently, the leaves of insectivorous plants show various types of modification. Example-Pitcher plant, sundew, etc.

Question 21. What are decomposers?
Answer:

Decomposers:

Decomposers are microorganisms, which putrefy or decompose the dead organisms and excretory materials to liberate simple elementary components from complex organic matter.

Example-Different bacteria and fungi.

Question 22. What role do the decomposers play in the environment?
Answer:

Role of the decomposers play in the environment

Decomposers putrefy dead organisms and excretory materials and convert complex organic matters into simple matters. This process maintains the reserve of elements in the environment, thus, maintaining the balance among different elementary nutrients.

Other than this, decomposers keep the environment clean by disposing of the decaying matter.

Question 23. Relate the following phenomena with the trend of disturbance in the nitrogen cycle resulting from different human activities-

1. Global warming,
2. Acidification of soil and water of rivers and lakes.

Answer:

Global warming:

Around 40% increase of N₂0 (nitrous oxide) in the environment is due to human activities. N₂0 is released in the environment as a result of the combustion of fossil fuel and the overuse of nitrogen-rich fertilizers.

This N₂O is a greenhouse gas that absorbs infrared radiation or heat of the sunlight which reflects on the earth and facilitates the greenhouse effect and global warming.

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Acidification of soil and water of rivers and lakes:

Oxides of nitrogen get dissolved in rainwater and form nitric acid, which is a major component of acid rain. Acid rain destroys aquatic plants and animals and disrupts the ecological equilibrium of rivers lakes, ponds, etc.

Apart from this, the destruction of forest resources, harm to architecture and monuments take place due to acid rain.

Question 24. How does acidification affect the environment?
Answer:

Air-polluting gases like nitric oxide (NO), other nitrogenous oxides, sulfur oxides, etc. mix. with rainwater and come down as acid rain.

This acidic rainwater mixes with soil and different water bodies to acidify them which harm the how acidification affects the environment. various components of the environment. This is how acidification affects the environment.

Question 25. Mention the significance of the nitrogen cycle.
Answer:

The significance of the nitrogen cycle are as follows-

1. The nitrogen cycle helps to maintain the nitrogen balance in the environment.
2. The amount of nitrogen necessary for the synthesis of protein is supplied to the living bodies from the nitrogen cycle. By this process, the nitrogen cycle helps in sustaining the race of life.

Chapter 5 Nitrogen Cycle Multiple Choice Question And Answers

Question 1. The most abundant gas in the atmosphere is—

1. Oxygen
2. Hydrogen
3. Carbon dioxide
4. Nitrogen

Answer: 4. Nitrogen

Question 2. Which of the following is not involved with the nitrogen cycle?

1. Nitrification
2. Eutrophication
3. Ammonification
4. Denitrification

Answer: 2. Eutrophication

Question 3. The plant, which traps and consumes insects to fulfill the need for nitrogen, is—

1. Sarpagandha [Rauvolfia)
2. Nayantara (Catharanthus)
3. Sunflower
4. Pitcher plant

Answer: 4. Pitcher plant

Question 4. Plants can absorb nitrogen from the soil in the form of—

1. NO₂ only
2. N₂O
3. NO
4. NO₂ and NO₃

Answer: 4. NO₂ and NO₃

Question 5. A nitrogen-fixing bacterium is—

1. Nitrosomonas
2. Azotobacter
3. Nitrobacter
4. Mycobacterium

Answer: 2. Azotobacter

Question 6. The microorganism inhabiting the root nodules of a sweet pea plant is—

1. Nostoc
2. Anabaena
3. Chlamydomonas
4. Rhizobium

Answer: 4. Rhizobium

Question 7. Ammonification is the formation of—

1. Ammonia from nitrates by decomposers
2. Ammonia from nitrogen
3. Ammonia from amino adds
4. Ammonia from nitrates by nitrogen fixers

Answer: 3. Ammonia from amino adds

Question 8. Which of the following is not a nitrogen-fixing bacterium?

1. Rhizobium
2. Mycobacterium
3. Nostoc
4. Azotobacter

Answer: 2. Mycobacterium

Question 9. The majority of nitrogen fixation occurs by—

1. Biological nitrogen-fixing organisms
2. The natural process by lightning
3. Volcanic eruptions
4. Haber-Bosch process

Answer: 1. Biological nitrogen-fixing organisms

Question 10. Which of the following components is increased in soil due to the cultivation of leguminous plants in it?

1. Oxygen
2. Carbon dioxide
3. Sulfur dioxide
4. Nitrogen

Answer: 4. Nitrogen

Question 11. Application of nitrogen in soil—

1. Reduces fertility
2. Increases fertility
3. Has no effect on fertility
4. Increases pH

Answer: 2. Increases fertility

Question 12. The percentage of nitrogen in the atmosphere is about—

1. 0.08
2. 20.60
3. 1.40
4. 78.09

Answer: 4. 78.09

Question 13. The component of air, which neither plants nor animals can absorb directly, is—

1. Oxygen
2. Carbon dioxide
3. Nitrogen
4. Both 1 and 2

Answer: 3. Nitrogen

Question 14. The enzyme by which nitrogen-fixing bacteria anaerobically convert atmospheric nitrogen into ammonia is—

1. Nitrogenase
2. Amylase
3. Pectinase
4. Galactase

Answer: 1. Nitrogenase

Question 15. The conversion of ammonia into nitrate is called—

1. Ammonification
2. Denitrification
3. Calcification
4. Nitrification

Answer: 4. Nitrification

Question 16. The blue-green algae capable of absorbing nitrogen from the atmosphere is—

1. Chlamydomonas
2. Clostridium
3. Anabaena
4. Rhodochorton

Answer: 3. Anabaena

Question 17. A nitrogen-releasing bacterium is—

1. Thiobacillus
2. Rhizobium
3. Nostoc
4. Diatom

Answer: 1. Thiobacillus

Question 18. The bacteria, which can trap at”losp^ nitrogen in the soil in the form of nitrogenous compounds, are called—

1. Symbiotic bacteria
2. Ammonifying bacteria
3. Nitrogen-fixing bacteria
4. Saprophytic bacteria

Answer: 3. Nitrogen-fixing bacteria

Question 19. Bacillus mycoides is a type of—

1. Symbiotic bacterium
2. Ammonifying bacterium
3. Denitrifying bacterium
4. Nitrifying bacterium

Answer: 2. Ammonifying bacterium

Question 20. Which of the following is correct regarding the nitrogen cycle?

1. N₂ cycle is a bio-geochemical cycle
2. The major reservoir of N₂ is the atmosphere
3. N₂ is the most abundant nutrient for plants
4. All of these

Answer: 4. All of these

Question 21. A soil-dwelling free-living nitrogen-fixing bacterium is—

1. Clostridium
2. Nostoc
3. Anabaena
4. Diatom

Answer: 1. Clostridium

Question 22. Nitrate in the soil is transformed into ammonia and then into free nitrogen by bacterial action. This process is called—

1. Nitrification
2. Ammonification
3. Denitrification
4. Symbiosis

Answer: 3. Denitrification

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Question 23. Which of the following nitrogenous compounds is increased in the atmosphere due to human activity?

1. N₂O
2. NO
3. NH₃
4. All of these

Answer: 4. All of these

Question 24. A nitrogenous greenhouse gas is—

1. NH₃
2. N₂O
3. HNO₃
4. All of these

Answer: 2. N₂O

Question 25. The nitrogenous compounds responsible for ozone depletion are—

1. NH₄OH and HNO₃
2. NO and NO₂
3. HNO₂ and HNO₃
4. NH₃ and HNO₂

Answer: 2. NO and NO₂

Question 26. The nitrogenous compound responsible for acid rain is—

1. NO₂
2. NO
3. HNO₃
4. All of these

Answer: 4. All of these

Question 27. Which of the following phase of the nitrogen cycle Pseudomonas is associated with?

1. Nitrogen fixation
2. Nitrification
3. Denitrification
4. Amnonification

Answer: 3. Denitrification

Question 28. Which of the following microbes take part in nitrification?

1. Nitrosomonas
2. Azotobacter
3. Pseudomonas
4. Thiobacillus

Answer: 1. Nitrosomonas

Chapter 5 Nitrogen Cycle Answer In A Single Word Or Sentence

Question 1. Name the process of cyclic rotation of various elements and inanimate matters in the biosphere.
Answer: Bio-geochemical cycle

Question 2. Mention the role of the biogeochemical cycle.
Answer: Bio-geochemical cycle maintains the balance among different elements of the environment.

Question 3. Name a gas that is essential for all plants but they cannot absorb it directly from the atmosphere.
Answer: Nitrogen

Role of Bacteria in the Nitrogen Cycle

Question 4. Name a denitrifying bacterium.
Answer: Thiobacillus denitrificans

Question 5. Mention the types of microorganisms which help in the biological fixation of nitrogen in the soil.
Answer: Biological nitrogen fixation occurs in soil by free-living microorganisms and symbiotic microorganisms.

Question 6. Name the pinkish-red pigment present in the root nodules of leguminous plants.
Answer: Leghaemoglobin

Question 7. Name a nitrogen-fixing free-living bacterium.
Answer: Clostridium

Question 8. Name a nitrogen-fixing symbiotic bacterium.
Answer: Rhizobium leguminosarum

Question 9. Name a nitrifying bacterium.
Answer: Nitrosomonas

Question 10. In which form does nitrogen stay in soil?
Answer: Nitrogen stays in the soil in the form of nitrate and nitrite salts.

Question 11. Give examples of two cyanobacteria, which are capable of fixing nitrogen from the atmosphere.
Answer: Anabaena and Nostoc

Question 12. Which role is played by fungi in the environment?
Answer: Fungi play the role of decomposers in the environment.

Question 13. Name two plants which feed on insects to obtain nitrogen.
Answer: Pitcher plant and sundew plant

Question 14. Name the process where nitrates are converted into free nitrogen.
Answer: Denitrification

Question 15. Name the two steps of nitrification.
Answer: Nutrition and nitration

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Question 16. By which process of nitrification, nitrite is produced from ammonia?
Answer: Nutrition

Question 17. Which type of bacteria converts nitrates into free nitrogen?
Answer: Denitrifying bacteria

Question 18. Name the process of ammonia formation by the decomposition of dead and decaying organic matter.
Answer: Ammonification

Question 19. Name two non-leguminous nitrogen-fixing plants.
Answer: Pine and Azolla

Common Misconceptions About the Nitrogen Cycle

Question 20. Which enzyme helps to catalyze the reactions for N₂ fixation?
Answer: Nitrogenase

Question 21. Write down the names of two nitrogen-containing chemical fertilisers.
Answer: Urea [CO(NH₂)₂] and ammonium nitrate (NH₄NO₃)

Question 22. Name the process by which industrial nitrogen fixation occurs.
Answer: Haber-Bosch process

Question 23. Give an example of two natural problems created due to the abnormality of N₂ cycle.
Answer: Two natural problems created due to the abnormality of N₂ cycle are acid rain and global warming (due to increased concentration of greenhouse gas.)

Real-Life Applications of the Nitrogen Cycle

Question 24. NH_{3 \(\stackrel{\mathbf{A}}{\longrightarrow}\)} NO_{2 \(\stackrel{\mathbf{B}}{\longrightarrow}\)} NO₃ write down the names of two bacteria suitable in positions A and B.
Answer: A-Nitrosomonas, B-Nitrobacter

Question 25. Give an example of one human activity that hampers the N₂ cycle.
Answer: The use of nitrogen-rich fertilizers hamper the N₂ cycle.

Chapter 5 Nitrogen Cycle Fill In The Blanks

Question 1. The process of trapping atmospheric nitrogen in the soil is known as _________.
Answer: Nitrogen fixation

Question 2. _________ develops root nodules in the root system of leguminous plants.
Answer: Rhizobium

Question 3. Anabaena is an example of _________.
Answer: Cyanobacteria

Question 4. During lightning,_________ is produced in the atmosphere by the combination of nitrogen and oxygen.
Answer: No

Question 5. Nitrosomonas is a type of _________ bacterium.
Answer: Nitrifying

Question 6. _________ is a bacterium which helps in the conversion of nitrite into nitrate.
Answer: Nitrobacter

Question 7. Another name of ammonification is _________.
Answer: Mineralisation

Question 8. Pea, gram, and other pulses are known as _________ plants.
Answer: Leguminous

Question 9. Rhizobium is a _________ nitrogen-fixing bacterium.
Answer: Symbiotic

Question 10. NO, of atmosphere mixes with rainwater to produce _________ and nitric acid.
Answer: Nitrous

Question 11. Azotobacter is a _________ nitrogen-fixing bacterium.
Answer: Free-living

Question 12. At the _________ phase of the nitrogen cycle, ammonia is converted into nitrite and nitrate by the action of some bacteria.
Answer: Nitrification

Chapter 5 Nitrogen Cycle State True Or False

Question 1. Nitrosomonas is a denitrifying bacterium.
Answer: False

Question 2. The Haber-Bosch reaction is a natural process of nitrogen fixation.
Answer: False

Question 3. Clostridium is a free-living nitrogen-fixing bacterium.
Answer: True

Question 4. Ammonia dissolves in water to produce nitrous acid and nitric acid.
Answer: False

Question 5. The bacterial species helping in the ammonification process is Bacillus mycoides.
Answer: True

Question 6. Nostoc is capable of absorbing atmospheric nitrogen.
Answer: True

Question 7. Azotobacter releases free nitrogen from nitrates, trapped in soil.
Answer: False

Question 8. The content of nitrogen in the atmosphere is 28.09%.
Answer: False

Question 9. Anabaena is an example of a symbiotic microorganism.
Answer: True

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Question 10. The other name of ammonification is mineralization.
Answer: True

Question 11. Carbon dioxide is a nitrogenous greenhouse gas.
Answer: False

Question 12. Bacteria act as decomposers but fungi do not.
Answer: False

 

Chapter 5 Nitrogen Cycle Match The Columns

1.

Answer: 1-B; 2-C; 3-D; 4-A; 5-E; 6-G

2.

Answer: 1-E; 2-D; 3-B; 4-A; 5-C; 6-F

 

Chapter 5 Nitrogen Cycle Find The Odd One Out

Question 1. Azotobacter, Rhizobium, Clostridium, Anabaena
Answer: Anabaena

Question 2. Nitric acid, Nitric oxide, Ammonia, Nitrogen dioxide
Answer: Ammonia

Question 3. Nitrification, Denitrification, Industrial N₂ fixation, Nitrite formation
Answer: Industrial N₂ fixation

Question 4. Nitrosomonas, Nitrococcus, Clostridium, Nitrobacter
Answer: Clostridium

Chapter 5 Nitrogen Cycle Fill In The Blanks By Looking At The First Pair

Question 1. Clostridium Free-living bacterium Rhizobium:_________
Answer: Symbiotic bacterium

Question 2. Sweet pea plant: Rhizobium :: Azolla:_________
Answer: Anabaena

Question 3. Nitrogen fixation: Azotobacter:: Nitrification: _________
Answer: Nitrobacter

Question 4. Ammonifying bacteria: Bacillus mycoides:: _________: Nitrosomonas
Answer: Nitrifying bacteria

Question 5. Nitric oxide: Photochemical smog:: Nitrous oxide: _________
Answer: The greenhouse effect

Question 6. Nitrobacter: Nitrification:: Bacillus mycoides: _________
Answer: Ammonification

Chapter 5 Nitrogen Cycle Among The Four Concepts Given Three Of Them Belong To One Find That

Question 1. The action of Bacillus ramosus, Breakdown of amino acids, Action of Bacillus mycoides, Ammonification
Answer: Ammonification

Question 2. Nitritation and nitratation, Action of Nitrobacter, Nitrification, Action of Nitrosomonas
Answer: Nitrification

Question 3. Nitrosomonas, Nitrococcus, Nitrobactor, Nitrifying bacteria
Answer: Nitrifying bacteria

Question 4. Biological N₂ fixation, Rhizobium, Azolla, Azotobacter
Answer: Biological N₂ fixation

Question 5. Clostridium, Nostoc, Rhizobium, N₂ fixing microbes
Answer: N₂ fixing microbes

Question 6. Acid rain, Greenhouse gas formation, PAN formation, Abnormality of N₂, cycle
Answer: Abnormality of N₂, cycle