Class 9 Science: Earth as a System – Practice Extra Questions

Ans: C

Explanation: Cover cropping involves planting non-cash crops between harvest and planting of the main crop. These cover crops, when tilled back into the soil or left to decompose on the surface, significantly increase the soil’s organic matter content. Higher organic matter improves soil structure, making it more cohesive and thus more resistant to being detached and transported by wind. Deep plowing can disrupt soil structure and bring less fertile subsoil to the surface, potentially increasing erosion. Monoculture farming, or planting the same crop year after year, can deplete soil nutrients and organic matter, making it more vulnerable. Excessive use of chemical fertilizers can provide nutrients but does not directly increase organic matter; in fact, reliance on them can sometimes neglect practices that build organic matter.
Correct Option: C

Ans: C

Explanation: Particulate matter air pollution refers to tiny solid or liquid particles suspended in the air. Photosynthesis is a biological process that consumes carbon dioxide and produces oxygen, not particulate matter. Evaporation of water results in water vapor, which is a gas, not particulate matter. Volcanic eruptions do release significant amounts of particulate matter into the atmosphere, but burning fossil fuels for transportation is a widespread and continuous source of anthropogenic particulate matter pollution in urban and industrialized areas. Therefore, burning fossil fuels for transportation is a primary source of particulate matter air pollution.
Correct Option: C

Ans: C

Explanation: Nuclear power plants do not burn fossil fuels, so they do not release greenhouse gases like carbon dioxide, which contribute to climate change. While nuclear power does produce radioactive waste, this is a manageable issue compared to the continuous emission of air pollutants from fossil fuel combustion. Fossil fuels, when burned, release harmful pollutants such as sulfur dioxide and nitrogen oxides, which are major contributors to smog and respiratory problems. Furthermore, the extraction of fossil fuels often requires significant land use for mining or drilling operations. Therefore, the minimal release of air pollutants is a significant environmental benefit of nuclear power over fossil fuels.
Correct Option: C

Ans: A

Explanation: Nanotechnology involves the manipulation of matter on an atomic and molecular scale. This miniaturization allows for the creation of materials with unique properties, such as enhanced light absorption and improved charge separation, which are crucial for developing more efficient solar energy harvesting systems. Biotechnology focuses on biological systems, geotechnology on the Earth’s crust, and astrobiology on life in the universe; none of these directly address the development of advanced solar energy materials in the way nanotechnology does.
Correct Option: A

Ans: D

Explanation: Geothermal energy harnesses heat from within the Earth. Wind energy captures the kinetic energy of moving air. Tidal energy utilizes the rise and fall of ocean tides. Solar photovoltaic energy, on the other hand, directly converts sunlight into electricity using photovoltaic cells, without the involvement of biomass or water.
Correct Option: D

Ans: D

Explanation: The question describes a situation where a community prioritizes immediate economic gain from mining a rare earth element, deliberately ignoring potential environmental damage. This approach is inherently unsustainable. Option A describes sustainable development, which is the opposite of what is happening. Option B suggests the economy will be stable for centuries, which is unlikely given resource depletion. Option C presents positive environmental outcomes, which are explicitly stated as being ignored. Option D accurately reflects the consequences of depleting a resource and causing ecological harm, which will inevitably limit future economic opportunities.
Correct Option: D

Ans: B

Explanation: Rajasthan and Gujarat are characterized by low rainfall and high temperatures, which are the defining features of an arid climate. While some parts might experience semi-arid conditions, the predominant climatic zone for much of these states, especially Rajasthan, is arid.
Correct Option: B

Ans: A

Explanation: Lichens are symbiotic organisms composed of fungi and algae. The fungal component can absorb moisture and nutrients from the atmosphere and the substrate. Importantly, lichens produce organic acids and chelating agents that can chemically break down rock minerals. This process, known as chemical weathering, is a significant initial step in the long-term formation of soil. Option B is incorrect because while lichens absorb water, their expansion is not a primary mechanism for physically breaking rocks on a large scale; it’s the chemical action that’s key. Option C is incorrect as lichens do not attract insects in a way that causes them to burrow into rocks for weathering. Option D is incorrect; lichens do not produce magnetic fields.
Correct Option: A

Ans: C

Explanation: The biosphere is the sum of all ecosystems. It is the part of Earth where life exists. This includes all living organisms and their environments, encompassing the lower parts of the atmosphere, the entire hydrosphere (oceans, lakes, rivers, and groundwater), and the upper parts of the lithosphere (Earth’s crust). Therefore, it is found where these three spheres interact.
Correct Option: C

Ans: D

Explanation: The greenhouse effect is caused by certain gases in the Earth’s atmosphere that trap heat. These gases, known as greenhouse gases, include methane (CH4), carbon dioxide (CO2), and chlorofluorocarbons (CFCs), among others. All of these substances are potent greenhouse gases.
Correct Option: D

Ans: D

Explanation: The movement of water on Earth, known as the water cycle, is primarily driven by solar energy. The sun’s heat causes water to evaporate from oceans, lakes, and rivers into the atmosphere. This water vapor then condenses to form clouds, and eventually falls back to Earth as precipitation (rain, snow, etc.). This continuous process of evaporation, condensation, and precipitation is the engine of the water cycle and is powered by the sun. Trees play a role in transpiration, which is the release of water vapor from plants, but this is a secondary effect of solar energy driving plant processes. Mountains influence precipitation patterns but are not the primary energy source. Water itself is the substance being moved, not the energy source.
Correct Option: D

Ans: A

Explanation: Temperature is a critical factor for the metabolic processes of aquatic organisms, including reproduction. Changes in temperature can trigger or inhibit breeding cycles, affecting population dynamics. While temperature can indirectly influence plant growth and nutrient availability, and directly impact digestion, breeding is often a more direct and significant impact of temperature shifts in many aquatic species.
Correct Option: A

Ans: A

Explanation: A greenhouse is a structure that traps heat from the sun, creating a warmer environment than the outside. This phenomenon is analogous to how greenhouse gases in the Earth’s atmosphere trap heat, leading to an increase in the Earth’s average temperature, a process known as global warming. Terrace gardening, kitchen gardens, and the increase in algae growth are not directly or primarily related to the greenhouse effect.
Correct Option: A

Ans: D

Explanation: SPN likely refers to Suspended Particulate Matter (SPM) or a similar term related to air pollution. Suspended Particulate Matter is a general term for a mixture of solid particles and liquid droplets suspended in the air. Fly ash is a byproduct of burning coal. Dust is fine particles of solid matter. Soot and smoke are also particulate matter produced from incomplete combustion. Therefore, all the listed components can be found in suspended particulate matter.
Correct Option: D

Ans: B

Explanation: The assertion that forests are a renewable resource is true because trees can be replanted and regrown. The justification that protecting forests provides numerous advantages is also true, as forests offer ecological, economic, and social benefits. However, the justification does not directly explain *why* forests are a renewable resource. The advantages of forests, while significant, are consequences of their renewability, not the reason for their renewability itself. Therefore, the reason is true but does not explain the assertion.
Correct Option: B

Ans: A

Explanation: Denitrification is the process by which certain bacteria convert nitrates (NO3-) back into nitrogen gas (N2), which is then released into the atmosphere. This is a crucial part of the nitrogen cycle, as it returns atmospheric nitrogen to the soil and water. Nitrification is the conversion of ammonia to nitrates. Nitrogen fixation is the conversion of atmospheric nitrogen into ammonia. Excretion is the elimination of metabolic waste products.
Correct Option: A

Ans: A

Explanation: Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create their own food (glucose) and release oxygen. Carbon dioxide from the atmosphere is a key reactant. Respiration is the process by which organisms break down glucose in the presence of oxygen to release energy, and carbon dioxide is a byproduct that is released back into the atmosphere. Therefore, carbon, in the form of carbon dioxide, is continuously circulated between the atmosphere, organisms, and the environment through these two processes. Water is involved in photosynthesis but is not the primary substance circulated by both processes in terms of a large-scale environmental cycle driven by both. Nitrogen is primarily cycled through the nitrogen cycle, and hydrogen is a component of many molecules but not the central element circulated by both photosynthesis and respiration in this context.
Correct Option: A

Ans: B

Explanation: The carbon cycle describes the movement of carbon atoms between the Earth’s atmosphere, oceans, land, and living organisms. Photosynthesis is the process by which plants remove carbon dioxide from the atmosphere. Respiration is the process by which living organisms release carbon dioxide into the atmosphere. The burning of fossil fuels releases large amounts of carbon dioxide into the atmosphere. Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is a physical process that primarily involves water and does not directly involve the significant movement of carbon atoms in the same way as the other options.
Correct Option: B

Ans: C

Explanation: The conversion of ammonia to nitrite is the first step in the process of nitrification, which is carried out by specific bacteria. Nitrogen fixation is the conversion of atmospheric nitrogen into ammonia. Nitrogenation is a general term for the addition of nitrogen to a compound or system. Denitrification is the conversion of nitrates back into nitrogen gas. Therefore, nitrification is the correct term for the conversion of ammonia to nitrite.
Correct Option: C

Ans: C

Explanation: Voltaic cells, also known as galvanic cells, generate electricity through spontaneous redox (reduction-oxidation) reactions. These chemical reactions involve the transfer of electrons from one substance to another. This electron transfer creates an imbalance of charge, leading to a potential difference, or voltage, between the two electrodes. Mechanical and thermal effects are not the primary causes of voltage generation in voltaic cells, although temperature can influence the rate of the chemical reactions.
Correct Option: C