Chapter 5 – (a) Nitrogen Cycle | Life Science Solution Class 10

Objective-type questions (MCQ)

Question 1

Answer

78.17%

Explanation:

The approximate percentage of N2 gas in the atmosphere is 78.17%.

Question 2

1. Nitrification
2. Ammonification
3. Denitrification
4. Nitrogen assimilation.

Answer

Ammonification

Explanation:

The process of release of ammonia and its formation to ammonium ions is known as ammonification.

Question 3

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

Answer

nitrification

Explanation:

The process of converting ammonia to nitrate is known as nitrification.

Question 4

Answer

77.17%

Explanation:

Nitrogen gas (N₂) makes up approximately 77.17% of the Earth’s atmosphere.

Very Short-Answer (VSA) type questions

Question 1

Mention the percentage of N₂ in the atmosphere.

Answer

The percentage of N₂ in the atmosphere is approximately 77.17%.

Question 2

Name one nitrifying bacteria.

Answer

Nitrosomonas is a nitrifying bacteria.

Question 3

Name one denitrifying bacteria. 

Answer

Pseudomonas.

Question 4

Name a bacterium which can fix nitrogen from the air. 

Answer

Rhizobium is a bacterium which can fix nitrogen from the air.

Question 5

What is Rhizobium?

Answer

Question 6

Name algae which can trap atmospheric nitrogen.

Answer

Anabaena is an example of algae that can trap atmospheric nitrogen.

Question 7

Which is the general source of nitrogen for higher plants?

Answer

The general source of nitrogen for higher plants is the soil.

Question 8

From where do the animals get nitrogen?

Answer

Animals get nitrogen by consuming plants or other animals that have consumed plants. Nitrogen is an essential component of proteins, DNA, and other biomolecules necessary for animal growth and development.

Fill in the blanks

Question

1. ____ is a kind of nitrifying bacteria.
2. In the Nitrogen Cycle Nitrobacter converts nitrites into ____.
3. ____ and nitrites into free are ammonifying bacteria.
4. Denitrifying bacteria converts nitrate and nitrites into free ____.

Answer

1. Nitrosomonas
2. nitrates
3. ammonia
4. nitrogen

Short-Answer (SA) type questions

Question 1

Name two nitrifying bacteria. 

Answer

Nitrosomonas and Nitrobacter are two examples of nitrifying bacteria.

Question 2

Answer

Two examples of denitrifying bacteria are Pseudomonas and Bacillus.

Question 3

What is Nitrogen Cycle?

Answer

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into various chemical forms as it circulates through the air, water, and soil of the earth. The cycle consists of several processes such as nitrogen fixation, nitrification, ammonification, and denitrification, which collectively convert nitrogen between different forms and make it available for use by living organisms.

Question 4

Mention the importance of nitrogen for the organism.

Answer

• Nitrogen is an essential component of nucleic acids and proteins, which are vital for the growth and reproduction of living organisms.
• It is a key element in the structure of chlorophyll, the pigment that is used by plants to convert sunlight into energy through photosynthesis.
• Nitrogen is also a major component of the Earth’s atmosphere, which is important for the climate and weather patterns.

Question 5

Define the biogeochemical cycle. 

Answer

Question 6

What is Nitrogen Cycle? What is nitrogen fixation ? 

Answer

The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms in the environment, including in the atmosphere, soil, and living organisms.

Nitrogen fixation is the process by which atmospheric nitrogen gas is converted into a usable form, such as ammonia or nitrate, by certain bacteria, including symbiotic bacteria found in the roots of leguminous plants. This process is essential for making nitrogen available for use by plants and other organisms.

Question 7

Discuss the significance of the cycle relation of the elements like C, O₂ and N₂ in the environment. 

Answer

The cycling of carbon, oxygen, and nitrogen is essential for maintaining the balance of nutrients and gases in the environment, which supports life on Earth.

1. The carbon cycle regulates the amount of carbon dioxide in the atmosphere, which affects the Earth’s climate.
2. The oxygen cycle ensures that there is a continuous supply of oxygen in the atmosphere, which is essential for respiration and the survival of aerobic organisms.
3. The nitrogen cycle is important for the production of amino acids, proteins, and DNA, which are essential components of all living organisms. It also ensures that there is a continuous supply of nitrogen for plant growth.

Question 8

Write the percentage of nitrogen, oxygen and carbon in the atmosphere.

Answer

• Nitrogen (N₂): Approximately 78.08%
• Oxygen (O₂): Approximately 20.90%
• Carbon Dioxide (CO₂): Approximately 0.04%

Long-Answer (LA) type questions

Question 1

What is Nitrogen Cycle? Describe it in brief with proper diagram.

Answer

Nitrogen cycle: The cyclical path, through which nitrogen is trapped in the lithosphere from the atmosphere, and then it comes into the living organisms from the lithosphere and finally returns to the atmosphere through a specific route, known as the nitrogen cycle.

Nitrogen cycle diagrammatical sketch

Question 2

Answer

Bacteria play a crucial role in fixing free nitrogen in the environment. Nitrogen fixation is the process by which atmospheric nitrogen is converted into nitrogenous compounds like ammonia, nitrates, and nitrites by the action of nitrogen-fixing bacteria. These bacteria have the enzyme nitrogenase that can break the strong triple bond between two nitrogen atoms and combine them with hydrogen to form ammonia.

The two important roles of organisms in supplying carbon dioxide in the environment. 

• Photosynthesis: Plants and some other organisms can absorb carbon dioxide from the atmosphere and convert it into organic compounds through photosynthesis.
• Respiration: Organisms also release carbon dioxide into the environment as a waste product of respiration. This carbon dioxide can be reabsorbed by photosynthetic organisms to continue the cycle.

Question 3

Discuss briefly the role of bacteria in releasing and fixing nitrogen in the environment.

Answer

Bacteria play a crucial role in the nitrogen cycle, which is the process by which nitrogen is converted into different forms that can be used by living organisms. Some bacteria are responsible for nitrogen fixation, which is the process of converting atmospheric nitrogen gas (N₂) into a form that can be used by plants and other organisms. This process involves the use of an enzyme called nitrogenase, which is found in certain bacteria. Other bacteria are involved in the process of denitrification, which is the conversion of nitrate (NO₃^–) back into nitrogen gas (N₂), which is then released back into the atmosphere. The overall result of these processes is the maintenance of a balance of nitrogen in the environment, which is essential for the growth and survival of all living organisms.

Drawing based questions

Question 1

Draw the chart of the Nitrogen Cycle.

Answer