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Environment and Biodiversity MCQs – 04 ( Nutrient cycles )

Most important MCQs from the chapter – Nutrient cycles  MCQs for UPSC, State PSC and Other Examinations.

Chapterwise MCQs

Short Notes

1. Solar radiation plays the most important role in which among the following ?

(a) Carbon cycle
(b) Oxygen cycle
(c) Water cycle
(d) Nitrogen cycle

Correct Answer –  (c) Water cycle

  • Solar radiation plays an important role in the water cycle. 
  • It helps in evaporation of water from various sources like ocean, rivers, ponds etc. 
  • It also facilitates melting of glaciers, Ice caps which contribute to the water cycle.

2. Carbon is present in the atmosphere, mainly in the form of ?

(a) Carbon dioxide
(b) Carbon monoxide
(c) Water
(d) Black Carbon

Correct Answer –  (a) Carbon dioxide

  • Carbon is present in the atmosphere, mainly in the form of carbon dioxide and Methane.
  • Carbon from the atmosphere moves to green plants by the process of photosynthesis.
  • When herbivore animals eat plants, Carbon enters the animal food chain.
  • By process of respiration and decomposition of dead organic matter, it returns back to the atmosphere.

3. Which of the following does not add carbon dioxide to the atmosphere ?

(a) Respiration
(b) Decay of organic matter
(c) Photosynthesis
(d) Volcanic eruptions

Correct Answer –  (c) Photosynthesis

  • Photosynthesis does not add carbon dioxide to the atmosphere. 
  • Carbon from the atmosphere moves to green plants by the process of photosynthesis. Hence it reduces the amount of carbon dioxide in the atmosphere.
  • Respiration, Decay of organic matter and Volcanic eruptions add carbon dioxide to the atmosphere.

4. Consider the following statements about Nitrogen:

1. Nitrogen is the most abundant gas in the Earth’s atmosphere.
2. Atmospheric Nitrogen can be used directly by most living organisms.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (a) 1 only

  • Nitrogen is the most abundant gas in the Earth’s atmosphere, making up to 78% of the atmospheric air.
  • However, Atmospheric Nitrogen can not be used directly by most living organisms.
  • Nitrogen needs to be converted to ammonia, nitrites or nitrates, before it can be used by plants. This process is called Nitrogen Fixation.

5. Consider the following statements about Nitrogen Fixation:

1. Certain microorganisms are capable of fixing atmospheric nitrogen into usable form which can be used by plants.
2. Rhizobium is a nitrogen-fixing bacteria.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (c) Both 1 and 2

  • Atmospheric Nitrogen needs to be converted to ammonia, nitrites or nitrates, before it can be used by plants. 
  • Certain microorganisms are capable of fixing atmospheric nitrogen into usable form which can be used by plants.
  •  Azotobacter, Rhizobium are a few examples of nitrogen-fixing bacteria.

6. Which of the following bacteria is able to convert the Nitrogen from Nitrite to Nitrate ?

(a) Azotobacter
(b) Rhizobium
(c) Nitrobacter
(d) Plasmodium

Correct Answer –  (c) Nitrobacter

  • Nitrobacter is able to convert the Nitrogen from Nitrite to Nitrate which is used by many plants.
  • This process is called nitrification.
  • It is to be noted here that nitrification plays an important role in the removal of ammonia from municipal wastewater.

7. Which of the following bacteria forms a symbiotic nitrogen-fixing association with roots of legumes ?

(a) Azotobacter
(b) Rhizobium
(c) Nitrobacter
(d) Plasmodium

Correct Answer –  (b) Rhizobium 

  • Rhizobium bacteria form a symbiotic nitrogen-fixing association with roots of legumes plants.
  • Rhizobium is a vital bacteria  as it provides nitrogen to agricultural soils including those in arid regions.
  • It increases soil productivity and soil fertility.

8. Consider the following statements about Denitrification:

1. In denitrification, nitrates/nitrites are converted into elemental nitrogen.
2. Pseudomonas is a denitrifying bacteria.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (c) Both 1 and 2

  • In the process of denitrification, nitrates/nitrites are converted into elemental nitrogen which is released back to the atmosphere.
  • Pseudomonas and Thiobacillus are examples of denitrifying bacteria.

9. Consider the following statements about Phosphorus:

1. Phosphorus is usually found in the form of phosphates.
2. It is a common ingredient in fertilizers.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (c) Both 1 and 2

  • Phosphorus is usually found in the form of phosphates.
  • It is found in Sedimentary rocks and minerals.
  • It is a common ingredient in fertilizers.
  • It also plays a major role in the formation of DNA.

10. Which among the following processes add sulfur to the atmosphere ?

(a) In the process of decomposition
(b) Volcanic eruptions
(c) Combustion of fossil fuels
(d) All of the above

Correct Answer –  (d) All of the above

  • Sulfur is added to the atmosphere in volcanic eruptions, combustion of fossil fuels from and from the gasses released during decomposition.
  • In the atmosphere, it exists in the form hydrogen sulfide (H2S) and sulfur dioxide (SO2).

11. Consider the following statements about Acid Rain:

1. It contains Sulfuric acid (H2SO4).
2. It is good for aquatic life in the oceans.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (a) 1 only

  • When SO2 (Sulphur Dioxide) and NOx (Nitrogen Oxide) combine with rain water and oxygen in the atmosphere, they form sulfuric acid (H2SO4) and nitric acid (HNO3) and cause Acid rain.
  • Effects of Acid Rain:
    • Increases acidity of Oceans, rivers and lakes which affects the survival of certain species.
    • Deterioration and discoloration of physical infrastructure(Example → Taj Mahal turning yellow due to sulfuric acid reactions).
    • Skin diseases in humans

12. In the Nitrogen Cycle, soil nitrates are transformed back into free nitrogen by which among the following ?

(a) Nitrifying bacteria
(b) Denitrifying bacteria
(c) Ammonifying bacteria
(d) None of the Above

Correct Answer – (b) Denitrifying bacteria

  • In the process of denitrification, nitrates/nitrites are converted into elemental nitrogen which is released back to the atmosphere.
  • It is carried out by denitrifying bacteria.
  • Pseudomonas and Thiobacillus are examples of denitrifying bacteria.

13. Which among the following is the driving force of all the ecosystems on the earth ?

(a) Solar energy
(b) Producer
(c) Carbon
(d) Biomass

Correct Answer – (a) Solar energy 

  • Solar energy is the main driving force of all the ecosystems on the earth. 
  • It is this energy that producers use for photosynthesis. 
  • Consumers are dependent upon producers for their food requirement.

14. Consider the following statements:

1. Ecological productivity decreases from the equator towards the poles.
2. Insolation increases from the equator towards the poles.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (a) 1 only

  •  The rate at which biomass is generated in an ecosystem is called ecological productivity. 
  • Ecological productivity decreases from the equator towards the poles.
  • Insolation decreases from the equator towards the poles.
  • As solar energy is the main driving force of all the ecosystems, with the decrease of Insolation from the equator towards the poles, ecological productivity also decreases.

15. Consider the following statements about carbon sink:

1. A carbon sink is a carbon pool that has the capability to take more carbon from the atmosphere than it releases.
2. Forests and Soils are examples of carbon sinks.

Select the correct statement(s) using the codes given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer – (c) Both 1 and 2

  • A carbon sink is a carbon pool that has the capability to take more carbon from the atmosphere than it releases.
  • They are an important part of the natural carbon cycle.
  • They help in climate change mitigation.
  • Examples of carbon sinks → Soils, Forests, Ocean, Wetlands like mangroves etc.

Also Read in Environment and Ecology MCQs :

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