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Test: Natural Resources- 2 - Class 9 MCQ


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20 Questions MCQ Test Biology for Class 9 - Test: Natural Resources- 2

Test: Natural Resources- 2 for Class 9 2024 is part of Biology for Class 9 preparation. The Test: Natural Resources- 2 questions and answers have been prepared according to the Class 9 exam syllabus.The Test: Natural Resources- 2 MCQs are made for Class 9 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Natural Resources- 2 below.
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Test: Natural Resources- 2 - Question 1
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The main source of fresh water in India is

Detailed Solution for Test: Natural Resources- 2 - Question 1

Rainfall is the main source of fresh water in India. From precipitation alone (including snowfall), India receives 4,000 cubic km water. Of this, monsoon rainfall from June to September alone accounts for about 3,000 cubic km. A good part of it is lost through the process of evaporation and plant transpiration. A large part of water percolated into the ground and is available to us in the form of groundwater.

Test: Natural Resources- 2 - Question 2
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The atmosphere of the earth is heated by radiations which are mainly

Detailed Solution for Test: Natural Resources- 2 - Question 2
The Atmosphere of the Earth is Heated by Radiations Mainly from:

A: Radiations Radiated by the Sun


- The sun is the primary source of heat and energy for the Earth's atmosphere.
- It emits electromagnetic radiations, including visible light, ultraviolet (UV) rays, and infrared (IR) radiation.

B: Radiations Re-radiated by Land


- Land surfaces absorb a portion of the solar radiation that reaches the Earth's surface.
- This absorbed energy is then re-radiated back into the atmosphere as heat.
- Land surfaces include continents, deserts, forests, and other terrestrial areas.

C: Radiations Re-radiated by Water


- Water bodies, such as oceans, lakes, and rivers, also absorb solar radiation.
- This absorbed energy is then released back into the atmosphere as heat.
- Water has a high heat capacity, meaning it can store and release a significant amount of heat energy.

D: Radiations Re-radiated by Land and Water


- Both land and water surfaces contribute to the heating of the Earth's atmosphere.
- Land and water surfaces absorb solar radiation and re-radiate it as heat, adding to the overall energy budget of the atmosphere.
Explanation:
- The sun is the primary source of heat for the Earth's atmosphere, emitting various types of radiations.
- Land surfaces and water bodies absorb a portion of the solar radiation and re-radiate it as heat.
- Both land and water contribute to the overall heating of the atmosphere.
- Therefore, the atmosphere of the Earth is heated by radiations that are re-radiated by both land and water (Option D).
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Test: Natural Resources- 2 - Question 3
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All of earth’s water, land and atmosphere, within which life exists is known as

Detailed Solution for Test: Natural Resources- 2 - Question 3
Answer:
The correct answer is A: biosphere.
Explanation:
The biosphere refers to all of Earth's water, land, and atmosphere, within which life exists. It is the zone where living organisms, including plants, animals, and microorganisms, interact with each other and their environment. Here is a detailed explanation of each option and why the answer is A:
- Option A: biosphere
- The biosphere includes all the ecosystems on Earth and is the sum total of all living organisms and their habitats.
- It encompasses the hydrosphere (water), lithosphere (land), and atmosphere, where life is sustained.
- This option is the correct answer as it accurately describes the entire system that supports life on Earth.
- Option B: population
- Population refers to a group of individuals of the same species living in the same area and time.
- While populations are a part of the biosphere, they do not encompass the entirety of Earth's water, land, and atmosphere.
- Option C: biome
- A biome is a large-scale community of plants and animals that occupy a specific region and have similar climatic conditions.
- Biomes are a subdivision of the biosphere and represent specific habitats within it.
- While biomes are an important aspect of the biosphere, they do not encompass the entire biosphere.
- Option D: communi
- It seems that there is a typo in this option, as it is incomplete. It is unclear what the full word should be.
- Without a complete word, it is impossible to determine the correct answer.
In conclusion, the correct answer is A: biosphere, as it represents the entirety of Earth's water, land, and atmosphere within which life exists.
Test: Natural Resources- 2 - Question 4
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If there were no atmosphere around the earth, the temperature of the earth will
Detailed Solution for Test: Natural Resources- 2 - Question 4
Explanation:
If there were no atmosphere around the Earth, the temperature of the Earth would be affected in several ways. Here is a detailed explanation:
1. Absence of Greenhouse Effect:
- The atmosphere plays a crucial role in trapping heat close to the Earth's surface through the greenhouse effect.
- Without an atmosphere, there would be no greenhouse effect, leading to a significant drop in temperature.
2. Temperature Variation:
- During the day, without an atmosphere, the Earth's surface would be directly exposed to the Sun's intense radiation, causing it to heat up rapidly.
- However, during the night, without an atmosphere to trap heat, the Earth's surface would radiate heat back into space, resulting in a rapid decrease in temperature.
3. Lack of Insulation:
- The atmosphere acts as an insulating layer, keeping the Earth's surface warm.
- Without it, the heat absorbed during the day would quickly dissipate into space, resulting in a much colder surface temperature.
4. Extreme Temperature Swings:
- The absence of an atmosphere would lead to extreme temperature swings between day and night.
- The surface temperature could reach scorching levels during the day, while dropping to extremely frigid temperatures during the night.
Conclusion:
- In the absence of an atmosphere, the temperature of the Earth would increase significantly during the day due to direct exposure to the Sun's radiation.
- However, it would decrease rapidly during the night as the surface radiates heat back into space.
- Therefore, the correct answer is C: Increase during the day and decrease during the night.
Test: Natural Resources- 2 - Question 5
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The nitrogen molecules present in air can be converted into nitrates and nitrites by
Detailed Solution for Test: Natural Resources- 2 - Question 5

The conversion of nitrogen molecules present in air into nitrates and nitrites can occur through a biological process known as nitrogen fixation. This process is carried out by specific bacteria that have the ability to convert atmospheric nitrogen gas (N2) into a form that can be utilized by plants and other organisms.
The detailed solution can be presented as follows:
1. Nitrogen fixation:
- Nitrogen fixation refers to the conversion of atmospheric nitrogen gas (N2) into a form that can be utilized by living organisms.
- This process is mainly carried out by certain bacteria, known as nitrogen-fixing bacteria, which can be found in the soil.
- These bacteria have the enzyme nitrogenase, which enables them to convert nitrogen gas into ammonia (NH3) through a series of biochemical reactions.
2. Biological process:
- Nitrogen fixation is a biological process that occurs naturally in the soil.
- The nitrogen-fixing bacteria present in the soil have a symbiotic relationship with certain plants, such as legumes (peas, beans, etc.).
- These bacteria form nodules on the roots of the plants and convert atmospheric nitrogen into a usable form.
- The plants, in turn, provide the bacteria with nutrients and a suitable environment for their growth.
3. Role of nitrates and nitrites:
- Nitrates (NO3-) and nitrites (NO2-) are important forms of nitrogen that can be taken up by plants and used for their growth and development.
- These compounds serve as a source of nitrogen for the synthesis of amino acids, proteins, and other essential biomolecules in plants.
- Nitrates and nitrites can also be further converted into various nitrogenous compounds, such as DNA, RNA, and chlorophyll, which play crucial roles in plant metabolism.
4. Other sources of nitrogen compounds:
- While nitrogen fixation by bacteria is the primary natural process for converting atmospheric nitrogen into nitrates and nitrites, there are also industrial processes that manufacture nitrogenous compounds.
- Industries involved in the production of fertilizers, explosives, and various chemical compounds utilize nitrogen fixation methods to convert nitrogen gas into usable forms.
- However, these industrial processes are not the main source of nitrates and nitrites in the environment.
In conclusion, the conversion of nitrogen molecules present in air into nitrates and nitrites primarily occurs through the biological process of nitrogen fixation carried out by specific bacteria present in the soil. This process plays a vital role in providing plants and other organisms with a usable form of nitrogen for their growth and survival.
Test: Natural Resources- 2 - Question 6
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Ozone layer is getting depleted because of
Detailed Solution for Test: Natural Resources- 2 - Question 6
Reasons for depletion of the ozone layer:

  • Excessive use of automobiles: The emissions from automobiles contain pollutants such as nitrogen oxides and volatile organic compounds. These pollutants can react with sunlight and contribute to the depletion of the ozone layer.

  • Excessive formation of industrial units: Industrial activities release pollutants such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) into the atmosphere. These chemicals are known to be major contributors to ozone depletion.

  • Excessive use of man-made compounds containing both fluorine and chlorine: Compounds containing fluorine and chlorine, such as CFCs and HCFCs, are commonly used in various industrial and consumer products. When released into the atmosphere, these compounds can reach the ozone layer and break down ozone molecules, leading to ozone depletion.

  • Excessive deforestation: Deforestation reduces the number of trees and plants that absorb carbon dioxide. As a result, there is an increase in the concentration of greenhouse gases in the atmosphere, which can indirectly contribute to ozone depletion.


Conclusion:
Among the given options, the excessive use of man-made compounds containing both fluorine and chlorine (option C) is the primary cause of ozone layer depletion. These compounds, such as CFCs and HCFCs, have been widely used in various industries and products, leading to their release into the atmosphere and subsequent damage to the ozone layer. It is crucial to reduce the use of these harmful compounds and implement stricter regulations to protect the ozone layer and prevent further depletion.
Test: Natural Resources- 2 - Question 7
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The amount of carbon dioxide in the atmosphere has increased in recent years. Environmentalists suggest this change is a direct result of the
Detailed Solution for Test: Natural Resources- 2 - Question 7
Explanation:
The correct answer is D: Overcutting of forests and the increased use of fossil fuels.
The increase in carbon dioxide in the atmosphere can be attributed to several factors, but the most significant ones are the overcutting of forests and the increased use of fossil fuels. Here is a detailed explanation of why these factors contribute to the increase in carbon dioxide levels:
1. Overcutting of forests:
- Forests act as carbon sinks, meaning they absorb carbon dioxide during photosynthesis and store it in their biomass.
- When forests are overcut or cleared for various purposes like agriculture or urbanization, the stored carbon is released back into the atmosphere.
- This release of carbon dioxide from deforestation adds to the overall carbon dioxide concentration in the atmosphere.
2. Increased use of fossil fuels:
- Fossil fuels, such as coal, oil, and natural gas, are carbon-rich energy sources that release carbon dioxide when burned.
- The burning of fossil fuels for electricity generation, transportation, and industrial processes has significantly increased over the years.
- This combustion process releases large amounts of carbon dioxide into the atmosphere, contributing to the greenhouse effect and global warming.
Other options mentioned, such as the dumping of inorganic materials into lakes and rivers, improper storage of solid and nuclear waste, and the use of herbicides and toxic substances, can have negative environmental impacts. However, they are not directly responsible for the increase in carbon dioxide levels in the atmosphere.
In conclusion, the overcutting of forests and the increased use of fossil fuels are the primary factors contributing to the increase in carbon dioxide levels in the atmosphere. It is crucial to address these issues through sustainable forest management and the transition to cleaner and renewable energy sources to mitigate the impact of climate change.
Test: Natural Resources- 2 - Question 8
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Low visibility during cold weather is due to
Detailed Solution for Test: Natural Resources- 2 - Question 8
Low visibility during cold weather is due to unburnt carbon particles or hydrocarbons suspended in the air.
Explanation:
- Cold weather can lead to poor visibility due to the presence of certain particles in the air.
- Unburnt carbon particles or hydrocarbons, which are byproducts of combustion processes, can become suspended in the air.
- These particles can be emitted from various sources, such as vehicle exhaust, industrial emissions, and burning of fossil fuels.
- During cold weather, these particles can linger in the air for longer periods of time and can become trapped close to the ground.
- The suspended particles can scatter and absorb light, reducing visibility and causing a haze or fog-like effect.
- This phenomenon is often referred to as smog or air pollution.
- It is important to note that low visibility during cold weather is not directly caused by the formation of fossil fuels or a lack of adequate power supply.
Therefore, the correct answer is B: unburnt carbon particles or hydrocarbons suspended in the air.
Test: Natural Resources- 2 - Question 9
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Smog is the mixture of
Detailed Solution for Test: Natural Resources- 2 - Question 9
Explanation:
The correct answer is C: smoke fog.
Smog is a type of air pollution that is a mixture of smoke and fog. It is formed when pollutants such as smoke, nitrogen oxides, and volatile organic compounds react with sunlight and heat in the atmosphere.
Here is a detailed breakdown of the components of smog:
- Smoke: Smoke is a component of smog that is produced by the burning of fossil fuels, such as coal, oil, and gas. It contains particulate matter, which includes tiny particles of dust, soot, and other pollutants.
- Fog: Fog is a component of smog that is formed when water vapor condenses in the air. It creates a thick, hazy layer that reduces visibility and can be harmful to breathe.
- Nitrogen: Nitrogen oxides, which are produced by the burning of fossil fuels and industrial processes, are also a component of smog. These pollutants can react with other compounds in the atmosphere to form smog.
- Ozone: Ozone is a gas that is a major component of smog. It is formed when nitrogen oxides and volatile organic compounds react with sunlight and heat. While ozone in the upper atmosphere is beneficial as it protects us from harmful UV radiation, ground-level ozone can be harmful to human health and the environment.
In conclusion, smog is a mixture of smoke and fog, along with other pollutants such as nitrogen oxides and ozone.
Test: Natural Resources- 2 - Question 10
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Choose the correct sequencs.
Detailed Solution for Test: Natural Resources- 2 - Question 10

The correct sequence is option B:
1. CO2 in atmosphere
2. Organic carbon in plants
3. Organic carbon in animals
4. Inorganic carbon in soil
Explanation:
1. CO2 in atmosphere: Carbon dioxide is present in the Earth's atmosphere as a greenhouse gas.
2. Organic carbon in plants: Plants absorb CO2 from the atmosphere through photosynthesis, converting it into organic carbon compounds.
3. Organic carbon in animals: Animals consume plants (or other animals) and incorporate the organic carbon compounds into their own bodies.
4. Inorganic carbon in soil: When plants and animals die, decomposers break down their organic matter, releasing CO2 back into the atmosphere. Some carbon, however, remains in the soil as inorganic carbonates.
Therefore, the correct sequence is CO2 in atmosphere → organic carbon in plants → organic carbon in animals → inorganic carbon in soil (option B).
Test: Natural Resources- 2 - Question 11
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In nutrient cycle, minerals tend to be dispersed through
Detailed Solution for Test: Natural Resources- 2 - Question 11
Mineral Dispersal in Nutrient Cycle:
The nutrient cycle involves the movement and recycling of essential minerals and nutrients in ecosystems. Minerals are dispersed through various processes to ensure their availability for plants and other organisms. The primary methods of mineral dispersal in the nutrient cycle include:
1. Surface and Sub-surface Runoff:
- Rainwater and melted snow carry dissolved minerals from the soil surface into rivers, lakes, and oceans.
- Groundwater movement also contributes to the transport of minerals through sub-surface runoff.
- These minerals eventually become part of the water bodies and may be utilized by aquatic organisms.
2. Weathering and Erosion:
- Physical and chemical weathering of rocks release minerals into the soil.
- Erosion processes, such as wind and water, transport these weathered minerals from one location to another.
- The transported minerals can then be utilized by plants through their root systems.
3. Decomposition and Organic Matter:
- Decomposers, such as bacteria and fungi, break down dead organic matter, releasing minerals into the soil.
- These minerals become available for absorption by plant roots and are subsequently incorporated into the food chain.
4. Biological Processes:
- Assimilation by plants and other organisms plays a crucial role in mineral dispersal.
- Plants absorb minerals from the soil through their roots and incorporate them into their tissues.
- When organisms consume plants or other animals, they obtain the minerals present in their tissues.
- Excretion and decomposition of waste products further contribute to the dispersal of minerals in the environment.
In summary, minerals in the nutrient cycle are dispersed through surface and sub-surface runoff, weathering and erosion, decomposition and organic matter, as well as biological processes like assimilation and excretion. These processes ensure the continuous movement and availability of minerals in ecosystems, supporting the growth and development of organisms.
Test: Natural Resources- 2 - Question 12
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What happens when rain falls on soil without vegetational cover?
Detailed Solution for Test: Natural Resources- 2 - Question 12
What happens when rain falls on soil without vegetational cover?


When rain falls on soil without vegetational cover, it can have several effects on the soil. The most significant ones are:
Rain water causes loss of surface soil:
- Without vegetational cover, raindrops directly hit the soil surface, causing the detachment and displacement of soil particles.
- This phenomenon is known as erosion, and it can lead to the loss of the top layer of fertile soil.
- The eroded soil can be washed away by the rainwater, causing soil erosion and sedimentation in nearby water bodies.
Increased runoff:
- In the absence of vegetation, rainwater cannot be absorbed by plant roots.
- This leads to increased surface runoff, as the water flows over the soil surface instead of infiltrating into the ground.
- Increased runoff can contribute to soil erosion, as it carries away soil particles and nutrients.
Reduced water infiltration:
- Soil without vegetational cover tends to have a compacted structure, with little pore space.
- As a result, rainwater cannot easily penetrate the soil surface and infiltrate into the ground.
- Reduced water infiltration can lead to surface runoff and loss of water that could have replenished groundwater reserves.
Decreased soil fertility:
- The loss of surface soil through erosion can result in a depletion of nutrients and organic matter.
- This can reduce the fertility of the soil, making it less suitable for plant growth.
- Without vegetational cover, there is also a lack of organic inputs, which are essential for maintaining soil fertility.
Overall, the absence of vegetational cover on soil can have negative consequences such as erosion, increased runoff, reduced water infiltration, and decreased soil fertility. It is important to implement measures to protect and restore vegetational cover to mitigate these effects and maintain the health and productivity of the soil.
Test: Natural Resources- 2 - Question 13
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Soil composition is dependent on weathering because
Detailed Solution for Test: Natural Resources- 2 - Question 13
Soil Composition and Weathering

Soil composition refers to the various components that make up soil, including minerals, organic matter, water, and air. Weathering, on the other hand, is the process of breaking down rocks and minerals into smaller particles through physical, chemical, and biological processes. The relationship between soil composition and weathering is significant because:


1. It contributes sediment to the soil:


- Weathering breaks down rocks and minerals into smaller particles, which become part of the soil composition.
- These sediment particles, such as sand, silt, and clay, contribute to the texture and structure of the soil.

2. It moves the topsoil to other areas where it is more needed:


- Weathering, particularly erosion caused by wind, water, and ice, can transport topsoil from one area to another.
- This movement of topsoil can redistribute nutrients and organic matter, making it more accessible to plants in different locations.

3. It makes the soil more fertile:


- Weathering processes release essential nutrients, such as potassium, calcium, and phosphorus, from rocks and minerals.
- These nutrients become available for uptake by plants, enhancing soil fertility and supporting plant growth.

4. It keeps the soil moist:


- Weathering can create pore spaces within the soil, allowing water to infiltrate and be stored.
- The presence of moisture in the soil is crucial for the survival of plants and the overall health of ecosystems.
In conclusion, weathering plays a vital role in soil composition by contributing sediment, redistributing topsoil, increasing fertility, and maintaining moisture levels. This relationship highlights the importance of understanding weathering processes in order to manage and maintain healthy soils for agriculture, forestry, and environmental conservation.
Test: Natural Resources- 2 - Question 14
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Top soil contains the following
Detailed Solution for Test: Natural Resources- 2 - Question 14

Top soil is the topmost and outermost layer of the soil, which is usually 2 inches to 8 inches layer. It is generally dark in colour due to humus, i.e., partially decayed organic matter, soil particles and living organisms as soil bacteria etc. 

Test: Natural Resources- 2 - Question 15
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Which of the following processes is involved in the water cycle?
Detailed Solution for Test: Natural Resources- 2 - Question 15
The Water Cycle:
The water cycle is a continuous process that involves the movement of water on, above, and below the Earth's surface. It is essential for the distribution and recycling of water throughout the planet. The main processes involved in the water cycle are:
1. Evaporation:
Evaporation is the process by which water changes from a liquid to a gas (water vapor) due to heat energy. It occurs when the sun's energy heats up bodies of water, such as oceans, lakes, and rivers, causing water molecules to gain enough energy to escape into the atmosphere.
2. Condensation:
Condensation is the process by which water vapor in the atmosphere cools and changes back into liquid water. It occurs when the warm air containing water vapor rises and cools, forming clouds. The water vapor molecules come together and form tiny water droplets or ice crystals.
3. Precipitation:
Precipitation refers to any form of water that falls from the atmosphere to the Earth's surface. It includes rain, snow, sleet, and hail. Precipitation occurs when the water droplets or ice crystals in the clouds become too heavy to be supported by the air and fall to the ground due to gravity.
4. Transpiration:
Transpiration is the process by which water vapor is released into the atmosphere by plants. It occurs when water is absorbed by plant roots and then evaporates from the leaves through small openings called stomata. Transpiration contributes to the overall moisture in the atmosphere.
5. Runoff and Infiltration:
When precipitation falls on land, it can either runoff over the surface, flowing into streams, rivers, and eventually into the oceans, or it can infiltrate into the ground, replenishing groundwater reserves. Runoff and infiltration play a crucial role in the water cycle by redistributing water across different parts of the Earth's surface.
In conclusion, the correct answer to the question is D: Evaporation, condensation, and precipitation. These processes are the key components of the water cycle, ensuring the continuous movement and distribution of water on Earth.
Test: Natural Resources- 2 - Question 16
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What would happen, if all the oxygen present in the environment is converted to ozone?
Detailed Solution for Test: Natural Resources- 2 - Question 16
What would happen if all the oxygen present in the environment is converted to ozone?
If all the oxygen present in the environment is converted to ozone, the following consequences would occur:
1. Lack of breathable air:
- Ozone cannot be breathed in by humans and other animals, as it is a highly reactive gas.
- The conversion of all oxygen to ozone would result in a shortage of breathable air, leading to suffocation and the inability to sustain life.
2. Toxicity:
- Ozone is a toxic gas, and high concentrations of it can have detrimental effects on living organisms.
- It can cause respiratory problems, eye irritation, lung damage, and other health issues.
- The conversion of all oxygen to ozone would result in an environment filled with toxic gas, posing a severe threat to all forms of life.
3. Disruption of ecosystems:
- Ozone is a powerful oxidizing agent that can harm plants by damaging their tissues and inhibiting photosynthesis.
- The conversion of all oxygen to ozone would lead to the destruction of plant life, disrupting ecosystems and negatively impacting the food chain.
4. Increased vulnerability to harmful sun radiations:
- Ozone plays a crucial role in protecting the Earth from harmful ultraviolet (UV) radiation from the sun.
- If all oxygen is converted to ozone, there would be a shortage of oxygen molecules to absorb UV radiation, resulting in increased exposure to harmful sun radiations.
- This would lead to an increased risk of skin cancer, cataracts, and other UV-related health issues for humans and animals.
In conclusion, if all the oxygen present in the environment is converted to ozone, it would result in a lack of breathable air, toxicity, disruption of ecosystems, and increased vulnerability to harmful sun radiations. This scenario would be highly detrimental to all forms of life.
Test: Natural Resources- 2 - Question 17
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In nitrogen cycle, which bacteria are responsible for nitrification?
Detailed Solution for Test: Natural Resources- 2 - Question 17
Nitrogen Cycle and Nitrification:
The nitrogen cycle is a vital process in the ecosystem that involves the transformation of nitrogen compounds between different forms. Nitrification is a key step in this cycle, where ammonia (NH3) is converted into nitrite (NO2-) and then into nitrate (NO3-).
Bacteria Responsible for Nitrification:
The process of nitrification is carried out by specific groups of bacteria. The bacteria responsible for nitrification are:
1. Nitrosomonas: Nitrosomonas bacteria are responsible for the oxidation of ammonia (NH3) to nitrite (NO2-). They convert ammonia into nitrite by oxidizing it, releasing energy in the process.
2. Nitrobacter: Nitrobacter bacteria are responsible for the oxidation of nitrite (NO2-) to nitrate (NO3-). They convert nitrite into nitrate by oxidizing it, releasing energy as well.
Role of Rhizobium:
Rhizobium is a type of bacteria that plays a crucial role in the nitrogen cycle, but it is not directly involved in nitrification. Rhizobium forms a symbiotic relationship with leguminous plants, where it converts atmospheric nitrogen into a usable form for the plants.
Role of Clostridium:
Clostridium is not involved in nitrification. It is a genus of bacteria that is known for its ability to produce endospores and can be found in various environments, including soil and the gut of animals.
In summary, the bacteria responsible for nitrification are Nitrosomonas and Nitrobacter. Rhizobium is involved in nitrogen fixation, and Clostridium has no direct role in nitrification.
Test: Natural Resources- 2 - Question 18
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Growth of lichens on barren rocks is followed by the growth of
Detailed Solution for Test: Natural Resources- 2 - Question 18
Explanation:
Introduction:
Lichens are composite organisms consisting of a symbiotic relationship between a fungus and a photosynthetic partner, usually algae or cyanobacteria. They are known to be pioneers in colonization and can grow on barren rocks, trees, soil, and other substrates.
Role of Lichens:
When lichens grow on barren rocks, they play a crucial role in initiating the process of primary succession. They are the first organisms to colonize these harsh environments and create favorable conditions for the growth of other plants. Here is a detailed explanation of the process:
- Pioneer Species: Lichens act as pioneer species, which are the first organisms to colonize an area devoid of vegetation.
- Breaking Down Rocks: The fungal component of lichens secretes enzymes that break down the rock surface, contributing to the weathering and erosion of the rocks.
- Soil Formation: As lichens continue to grow and decay, they contribute organic matter to the rock surface. This organic matter, along with the accumulation of dead lichen fragments, forms a thin layer of soil.
- Moisture Retention: The lichen thalli (body) can absorb and retain water, preventing rapid evaporation and creating a more favorable microclimate for other plants.
- Nutrient Availability: Lichens can also fix atmospheric nitrogen, making it available to other organisms in the ecosystem.
- Enhancing Succession: Once lichens have established themselves and created a suitable environment, other plants like mosses can start growing on the rocks. Mosses have shallow root systems and can take advantage of the thin layer of soil formed by lichens.
- Succession Continues: As mosses grow and decay, they further contribute to soil formation, moisture retention, and nutrient availability. This process continues, gradually paving the way for the growth of more complex plants like ferns, gymnosperms, and eventually, trees.
Conclusion:
In summary, the growth of lichens on barren rocks is followed by the growth of mosses. Lichens play a crucial role as pioneer species in initiating primary succession and creating a suitable environment for other plants to colonize. Mosses, being the next stage of succession, can grow on the thin layer of soil formed by lichens, further contributing to the development of the ecosystem.
Test: Natural Resources- 2 - Question 19
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Why is it difficult to integrate nitrogen gas from the atmosphere in the nitrogen cycle of the biosphere?
Detailed Solution for Test: Natural Resources- 2 - Question 19
Why is it difficult to integrate nitrogen gas from the atmosphere in the nitrogen cycle of the biosphere?
There are several reasons why it is difficult to integrate nitrogen gas from the atmosphere in the nitrogen cycle of the biosphere. These include:
1. Lack of direct utilization by most organisms:
- Atmospheric nitrogen gas (N2) is highly stable and does not readily react with other elements.
- Only a few microorganisms, called nitrogen-fixing bacteria, have the ability to convert atmospheric nitrogen into a biologically usable form, such as ammonia (NH3) or nitrate (NO3-).
- Most plants and animals cannot directly utilize atmospheric nitrogen and rely on nitrogen compounds produced by nitrogen-fixing bacteria.
2. Energy requirements for nitrogen fixation:
- The process of nitrogen fixation requires a significant amount of energy.
- Nitrogen-fixing bacteria use specialized enzymes to break the strong triple bond between nitrogen atoms in N2, which requires energy input.
- This energy requirement limits the ability of many organisms to directly convert atmospheric nitrogen into usable forms.
3. Availability of alternative nitrogen sources:
- Nitrogen is a vital nutrient for living organisms, and it can be obtained from various sources other than atmospheric nitrogen.
- Nitrogen compounds are present in soil, water, and organic matter, which can be readily utilized by plants and other organisms.
- As a result, many organisms have evolved to rely on these alternative nitrogen sources rather than depending on atmospheric nitrogen.
4. Rapid uptake and loss of nitrogen:
- Once nitrogen compounds are available in the biosphere, they can be rapidly taken up by plants and other organisms.
- Nitrogen is an essential component of proteins, nucleic acids, and other biomolecules, and living organisms have efficient mechanisms to absorb and utilize nitrogen.
- This quick uptake and utilization of nitrogen by organisms make it challenging to integrate atmospheric nitrogen into the nitrogen cycle.
In conclusion, the difficulty in integrating atmospheric nitrogen into the nitrogen cycle of the biosphere is primarily due to the limited ability of most organisms to directly utilize atmospheric nitrogen, the energy requirements for nitrogen fixation, the availability of alternative nitrogen sources, and the rapid uptake and loss of nitrogen by living organisms.
Test: Natural Resources- 2 - Question 20
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The process of nitrogen-fixation by bacteria does not take place in the presence of
Detailed Solution for Test: Natural Resources- 2 - Question 20

To understand why the process of nitrogen fixation by bacteria does not take place in the presence of elemental form of oxygen, let's break down the process and the conditions required for it to occur.
Nitrogen Fixation:
Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into a usable form by certain bacteria. These bacteria have the ability to convert nitrogen gas into ammonia (NH3) or nitrate (NO3-), which can then be utilized by plants and other organisms.
Conditions for Nitrogen Fixation:
Nitrogen fixation requires specific conditions to occur successfully. These conditions include:
1. Absence of Oxygen: Nitrogen-fixing bacteria are anaerobic, meaning they do not require oxygen for their metabolic processes. In fact, the presence of oxygen inhibits the activity of nitrogenase enzymes, which are responsible for the conversion of nitrogen gas into a usable form. Therefore, the process of nitrogen fixation cannot take place in the presence of elemental form of oxygen.
2. Symbiotic Relationship: Nitrogen-fixing bacteria often form symbiotic relationships with plants, such as legumes. These bacteria reside in specialized structures called nodules in the roots of these plants, providing them with a constant supply of fixed nitrogen while receiving carbohydrates and other nutrients in return.
3. Nitrogenase Enzymes: Nitrogen fixation is carried out by a group of enzymes called nitrogenase. These enzymes are highly sensitive to oxygen and can be irreversibly damaged when exposed to atmospheric concentrations of oxygen.
Answer:
Based on the above conditions, the correct answer is B: elemental form of oxygen. The presence of oxygen inhibits the activity of nitrogenase enzymes, preventing the process of nitrogen fixation by bacteria from occurring.
Note:
Water (option C) does not inhibit nitrogen fixation and can actually provide a suitable environment for the growth and activity of nitrogen-fixing bacteria. The molecular form of hydrogen (option A) and the elemental form of nitrogen (option D) are both involved in the process of nitrogen fixation and are not inhibitory factors.
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