Natural Resources, Science, Class 9 - Test - Class 9 MCQ

Micro-organisms that help in the formation of soil:
There are several micro-organisms that play a crucial role in the formation of soil. These micro-organisms break down organic matter and contribute to the nutrient cycle. The micro-organisms that help in the formation of soil include:
1. Bacteria:
- Bacteria are the most abundant micro-organisms in the soil.
- They decompose organic matter and release nutrients.
- Some bacteria also fix atmospheric nitrogen and make it available to plants.
2. Moss:
- Mosses are non-vascular plants that can grow in harsh environments, including barren soil.
- They help in the formation of soil by trapping and retaining moisture.
- Mosses also provide a substrate for other plants to grow on.
3. Lichen:
- Lichens are a symbiotic association between fungi and algae or cyanobacteria.
- They can grow on bare rocks and contribute to the weathering process.
- Lichens release organic acids that break down rocks and initiate soil formation.
4. (b) and (c):
- Both moss and lichen contribute to the formation of soil in different ways.
- Mosses help in moisture retention and provide a substrate for other plants.
- Lichens contribute to weathering and rock breakdown, initiating soil formation.
In conclusion, the micro-organisms that help in the formation of soil include bacteria, moss, lichen, and a combination of moss and lichen. These micro-organisms play a crucial role in breaking down organic matter, releasing nutrients, trapping moisture, and initiating the weathering process, leading to the formation of soil.

Burning of fossil fuels adds CO2, SO2, and NO2 gases in the air.
Explanation:
- Fossil fuels such as coal, oil, and natural gas are composed of carbon and hydrogen compounds.
- When these fuels are burned, the carbon and hydrogen react with oxygen in the air, resulting in the release of various gases.
- The main gas released is carbon dioxide (CO2), which is a greenhouse gas that contributes to global warming and climate change.
- The combustion process also produces sulfur dioxide (SO2) and nitrogen dioxide (NO2).
- Sulfur dioxide is a precursor to acid rain and can cause respiratory issues and damage to ecosystems.
- Nitrogen dioxide is a major component of smog and can cause respiratory problems and contribute to the formation of acid rain.
- Other gases such as carbon monoxide (CO), sulfur trioxide (SO3), and nitrogen trioxide (NO3) may also be emitted during the combustion process, but they are not as commonly produced as CO2, SO2, and NO2.
In conclusion, the correct answer is A: CO2, SO2, and NO2 gases are added to the air when fossil fuels are burned.

Greenhouse gases are:
- CO₂: Carbon dioxide is one of the most well-known greenhouse gases. It is produced through the burning of fossil fuels, deforestation, and other human activities.
- CH₄: Methane is another greenhouse gas that is released through natural processes such as the decay of organic matter and human activities such as agriculture and the production and transport of coal, oil, and natural gas.
- CFC: Chlorofluorocarbons (CFCs) are synthetic greenhouse gases that were commonly used in refrigeration, air conditioning, and aerosol propellants. They are now regulated due to their harmful effects on the ozone layer.
- All of these gases contribute to the greenhouse effect, which is the trapping of heat in the Earth's atmosphere, leading to global warming and climate change.
Summary:
Greenhouse gases include carbon dioxide (CO₂), methane (CH₄), and chlorofluorocarbons (CFCs). These gases contribute to the greenhouse effect and are responsible for global warming and climate change.

Nitrogen fixing can be done by rhizobium also. It is converted into inorganic nitrogen by them. Then it is incorporated into amino acids which are then used by plants.

Explanation:
The atmosphere plays a crucial role in maintaining the temperature on the surface of the Earth. Here's how it does it:
1. Presence of greenhouse gases:
- The atmosphere contains greenhouse gases like carbon dioxide, methane, and water vapor.
- These gases trap heat from the Sun, preventing it from escaping back into space.
- This process is called the greenhouse effect.
2. Insulation:
- The atmosphere acts as an insulating layer around the Earth.
- It holds air, which is a poor conductor of heat.
- This insulation helps to regulate the temperature, preventing extreme heat or cold.
3. Reflection of heat:
- The atmosphere reflects a small portion of the incoming solar radiation back into space.
- This reflection helps to reduce the amount of heat reaching the Earth's surface.
4. Absorption of heat:
- The atmosphere also absorbs some of the heat radiated by the Earth's surface.
- This absorption helps to prevent excessive heat buildup on the surface.
Conclusion:
In summary, the atmosphere maintains the temperature on the surface of the Earth by trapping heat through greenhouse gases, providing insulation, reflecting a portion of solar radiation, and absorbing heat radiated by the Earth's surface. Its composition and properties contribute to the overall temperature regulation of our planet.

Explanation:
Proteins are macromolecules composed of amino acids. These amino acids are linked together through peptide bonds to form a polypeptide chain, which then folds into a specific three-dimensional structure.
The amino acids that make up proteins contain several atoms, including carbon, nitrogen, and oxygen. These atoms are essential for the structure and function of proteins.
Here is a breakdown of the atoms present in protein molecules:
- Carbon: Carbon is a key component of all organic molecules, including proteins. It forms the backbone of the amino acids and provides stability to the protein structure.
- Nitrogen: Nitrogen is another important element found in proteins. It is present in the amino groups (-NH2) of amino acids and plays a crucial role in the formation of peptide bonds between amino acids.
- Oxygen: Oxygen is also a part of protein molecules. It is present in the carboxyl groups (-COOH) of amino acids and contributes to the overall structure and stability of the protein.
Therefore, the correct answer is d. all of these. Proteins contain carbon, nitrogen, and oxygen atoms, along with other elements such as hydrogen and sometimes sulfur or phosphorus, depending on the specific amino acids present.

Explanation:
Major components in the atmosphere of Mars and Venus are as follows:
1. Oxygen: Oxygen is not a major component in the atmospheres of Mars and Venus. On Mars, the atmosphere is composed of about 95% carbon dioxide and only traces of oxygen. Venus has a thick atmosphere predominantly consisting of carbon dioxide with only traces of oxygen.
2. Carbon dioxide: Carbon dioxide is the major component in the atmosphere of both Mars and Venus. On Mars, carbon dioxide makes up about 95% of the atmosphere, while on Venus it makes up about 96% of the atmosphere.
3. Nitrogen: Nitrogen is not a major component in the atmospheres of Mars and Venus. On Mars, nitrogen makes up less than 3% of the atmosphere, and on Venus, it is present in trace amounts.
4. Ozone: Ozone is not a major component in the atmospheres of Mars and Venus. Ozone is found in the Earth's atmosphere and plays a crucial role in protecting life from harmful ultraviolet (UV) radiation from the Sun.
Therefore, the correct answer is Carbon dioxide (B) as it is the major component in the atmospheres of both Mars and Venus.

Explanation:
The temperature on the moon ranges from -190°C to 110°C due to several factors related to its lack of atmosphere and water bodies. Here's a detailed explanation:
No atmosphere:
- The moon does not have a significant atmosphere like the Earth. It has an extremely thin exosphere, which consists of scattered atoms and molecules.
- Without a proper atmosphere, there is no insulation to regulate the temperature. The moon's surface is directly exposed to the extreme temperature variations of space.
Extreme cold:
- During the lunar night, which lasts approximately 14 Earth days, the absence of sunlight causes the temperature to drop drastically.
- The lack of an atmosphere means there is no blanket of air to trap heat, resulting in the surface temperature reaching as low as -190°C.
Extreme heat:
- Conversely, during the lunar day, which also lasts approximately 14 Earth days, the surface is exposed to the intense heat of the sun.
- Without an atmosphere to moderate the temperature, the surface can heat up to around 110°C, especially in regions directly under the sun.
No water bodies:
- The absence of water bodies on the moon also contributes to the temperature variations.
- Water has a high specific heat capacity, meaning it can retain heat and release it slowly. Without water bodies, the moon lacks this natural temperature regulation mechanism.
No bio-geo-chemical cycle:
- The moon does not have a bio-geo-chemical cycle like the Earth, which involves interactions between the atmosphere, land, and living organisms.
- On Earth, these cycles help regulate temperature and maintain a relatively stable climate. However, their absence on the moon contributes to the extreme temperature range.
In conclusion, the temperature variations on the moon are primarily due to its lack of atmosphere, absence of water bodies, and the absence of a bio-geo-chemical cycle. These factors result in extreme cold during the lunar night and extreme heat during the lunar day.

Depletion of Ozone Molecules in the Stratosphere

Ozone depletion refers to the decrease in the concentration of ozone molecules in the stratosphere. This depletion is primarily caused by the presence of certain chemical compounds known as halogen compounds.

Factors Contributing to Ozone Depletion:

• Chlorine Compound: Chlorofluorocarbons (CFCs) and other chlorine-containing compounds are major contributors to ozone depletion. These compounds are released from human activities such as aerosol propellants, refrigerants, and industrial processes.


• Fluorine Compound: Some fluorine-containing compounds, such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), also contribute to ozone depletion, although to a lesser extent compared to chlorine compounds.


• Halogen Compound: Halogen compounds, including chlorine and fluorine compounds, play a significant role in ozone depletion. They are stable and can persist in the atmosphere for extended periods, allowing them to reach the stratosphere and interact with ozone molecules.

Interaction with Ozone Molecules:

• When released into the atmosphere, chlorine and fluorine compounds undergo chemical reactions that ultimately release chlorine and fluorine atoms.


• These released atoms can then catalytically destroy ozone molecules in the stratosphere.


• Chlorine atoms, for example, can initiate a chain reaction by reacting with ozone molecules to form chlorine monoxide (ClO) and oxygen molecules.


• The chlorine monoxide can further react with other ozone molecules, resulting in a net reduction of ozone concentration.

Conclusion:

The depletion of ozone molecules in the stratosphere is primarily caused by the presence of halogen compounds, including chlorine and fluorine compounds. These compounds are released from human activities and can catalytically destroy ozone molecules through complex chemical reactions. It is essential to regulate and reduce the emissions of these compounds to mitigate ozone depletion and protect the ozone layer.

The life-supporting zone of earth is the biosphere.
The biosphere refers to the part of the Earth where life exists. It is made up of all the ecosystems on the planet, including the land, water bodies, and the atmosphere. Here are some key points explaining why the biosphere is the life-supporting zone of Earth:
1. Definition of the biosphere:
- The biosphere is the combination of all living organisms and their interactions with the environment.
- It includes all ecosystems, such as forests, oceans, deserts, and even areas underground.
2. Presence of life:
- The biosphere is the only zone on Earth where life is known to exist.
- It encompasses a wide range of organisms, from microscopic bacteria to large mammals, and everything in between.
3. Interconnectedness of ecosystems:
- Ecosystems within the biosphere are interconnected and rely on each other for survival.
- For example, plants produce oxygen through photosynthesis, which is essential for the survival of animals and humans.
4. Abundance of resources:
- The biosphere provides essential resources for life, such as food, water, and shelter.
- It supports a variety of ecosystems that sustain biodiversity and provide habitats for different species.
5. Regulation of climate:
- The biosphere plays a crucial role in regulating the Earth's climate.
- Through processes like photosynthesis and respiration, organisms exchange gases and help maintain the balance of greenhouse gases in the atmosphere.
6. Adaptability and resilience:
- The biosphere is dynamic and adaptable to changing environmental conditions.
- Organisms within the biosphere have evolved various mechanisms to survive and thrive in different habitats.
In conclusion, the biosphere is the life-supporting zone of Earth as it encompasses all ecosystems and provides the necessary conditions for the existence of life. It is a complex and interconnected web of living organisms and their interactions with the environment, making it vital for the survival of all species on the planet.