CBSE Class 9 Science Chapter 13 Earth As A System Energy, Matter, And Life MCQs Set 03

Multiple Choice Questions (MCQs) for Class 9 Science: Chapter 13 Earth As A System Energy, Matter, And Life

Access targeted multiple-choice questions for Chapter 13 Earth As A System Energy, Matter, And Life designed to align with the latest CBSE academic syllabus for Class 9 Science. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Practice Chapter 13 Earth As A System Energy, Matter, And Life MCQs for Class 9 Science

View or download the dedicated Chapter 13 Earth As A System Energy, Matter, And Life MCQ resource below. Practicing these 50 objective questions regularly builds familiarity with standard exam patterns and helps secure higher marks in final Science evaluations.

Question: Which of the Earth's five spheres is primarily responsible for storing and cycling liquid water through processes like evaporation, precipitation and groundwater flow?
A. Geosphere
B. Hydrosphere
C. Atmosphere
D. Biosphere
Show Answer & Explanation

Answer: (B) Hydrosphere

Explanation:
The hydrosphere encompasses all surface water bodies, groundwater, and other liquid water that moves through evaporation, condensation and precipitation. The geosphere is rock and soil, the atmosphere is air, and the biosphere is living organisms.

Question: Solar radiation reaching Earth is concentrated mainly in three wavelength ranges. Approximately what percentage of the Sun's total energy falls within these ranges?
A. About 50 percent
B. About 75 percent
C. About 99 percent
D. About 100 percent
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Answer: (C) About 99 percent

Explanation:
The chapter explicitly states that about 99 per cent of the Sun's energy reaching Earth is concentrated in the ultraviolet, visible and infrared wavelength ranges. The remaining energy is in other parts of the electromagnetic spectrum.

Question: Dark-coloured road surfaces heat up more quickly than light-coloured surfaces under identical sunlight because they have different values of what property?
A. Insolation
B. Albedo
C. Emissivity
D. Conductivity
Show Answer & Explanation

Answer: (B) Albedo

Explanation:
Albedo is the fraction of solar radiation that a surface reflects. Dark surfaces have low albedo, reflecting less light and absorbing more, causing them to heat up faster. Light surfaces have high albedo and stay cooler.

Question: In the troposphere, temperature decreases with altitude at a rate of approximately 6.5 degrees Celsius per kilometre. In contrast, the stratosphere above it shows the opposite pattern. Which of the following best explains why the stratosphere warms with altitude?
A. More solar radiation reaches the stratosphere than the troposphere
B. The ozone layer absorbs ultraviolet radiation and converts it to heat
C. Cold air naturally rises and accumulates in the stratosphere
D. The stratosphere is closer to the Sun than the troposphere
Show Answer & Explanation

Answer: (B) The ozone layer absorbs ultraviolet radiation and converts it to heat

Explanation:
• Ozone molecules in the stratosphere absorb harmful UV radiation
• This absorption of UV energy heats the stratosphere
• The lack of vertical mixing of air in the stratosphere due to this temperature inversion keeps weather confined to the troposphere below.

Question: During daylight hours in a mountainous valley, warm air from sunlit slopes rises while cooler valley air moves upward to replace it. What is this daytime wind pattern called?
A. Mountain breeze
B. Valley breeze
C. Planetary wind
D. Trade wind
Show Answer & Explanation

Answer: (B) Valley breeze

Explanation:
A valley breeze occurs during the day when sunlit mountain slopes heat more rapidly than the valley floor, creating rising warm air and a low pressure region. The cooler valley air flows upward to replace the rising air.

Question: Large circular patterns of ocean water circulation rotate clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere. These patterns are called what?
A. Currents
B. Tides
C. Gyres
D. Upwellings
Show Answer & Explanation

Answer: (C) Gyres

Explanation:
Gyres are large circular patterns formed by the deflection of moving water masses due to the Earth's rotation, with continents further modifying their paths. The text explicitly names these patterns and describes their rotation direction in each hemisphere.

Question: Which soil type has the lowest albedo and therefore absorbs the most solar radiation?
A. Snow
B. Light coloured soil
C. Black soil
D. Ice
Show Answer & Explanation

Answer: (C) Black soil

Explanation:
According to Table 13.1 in the chapter, black soil has a lower albedo than light coloured soil, meaning it reflects less radiation and absorbs more, making it relatively warmer.

Question: In the nitrogen cycle, which step describes the process by which decomposers break down dead organic matter and return nitrogen compounds like ammonia to the soil?
A. Nitrification
B. Denitrification
C. Ammonification
D. Assimilation
Show Answer & Explanation

Answer: (C) Ammonification

Explanation:
Ammonification is the process by which decomposers such as bacteria and fungi break down organic matter from dead plants and animals, returning nitrogen compounds like ammonia to the soil.

Question: The Haber-Bosch process, developed in the early 1900s, produces synthetic ammonia from atmospheric nitrogen. What major global achievement did this process enable?
A. Elimination of greenhouse gases from the atmosphere
B. Increased food production through agriculture by providing artificial fertilisers
C. Complete conversion of fossil fuels to renewable energy
D. Reversal of ocean acidification
Show Answer & Explanation

Answer: (B) Increased food production through agriculture by providing artificial fertilisers

Explanation:
The Haber-Bosch process revolutionised agriculture by enabling the production of most fertilisers used today, which facilitated India's Green Revolution and allowed feeding of billions of people worldwide.

Question: The chapter describes how atmospheric carbon dioxide has increased by about 35 per cent since 1960. Which human activities are primarily responsible for this increase?
A. Increased photosynthesis in forests and oceans
B. Burning of fossil fuels and deforestation
C. Increased albedo from urban areas
D. Enhanced plant respiration from agricultural expansion
Show Answer & Explanation

Answer: (B) Burning of fossil fuels and deforestation

Explanation:
Human activities like burning fossil fuels and deforestation have raised atmospheric CO₂ by about 35% since 1960, according to the chapter. This is an unprecedented rise in the history of human civilisation.

Question: When the chapter discusses eutrophication in water bodies, what sequence of events is triggered by excess nitrogen from agricultural runoff?
A. Water temperature increases, glaciers melt faster, sea levels rise
B. Algae grows excessively, depletes oxygen, kills fish and threatens fisheries
C. Soil becomes less dense, root systems weaken, crops fail
D. Atmospheric pressure decreases, storms form, monsoons intensify
Show Answer & Explanation

Answer: (B) Algae grows excessively, depletes oxygen, kills fish and threatens fisheries

Explanation:
Excess nitrogen via nitrates from fertilisers causes widespread growth of algae (algal blooms) that deplete oxygen and kill fish, threatening water bodies and coastal fisheries through a process called eutrophication.

Question: Warmer ocean water reduces the ocean's capacity to absorb carbon dioxide effectively. How does this response of the ocean to temperature increase create a problematic feedback for addressing climate change?
A. It increases photosynthesis, producing more oxygen
B. It reduces the ocean's role as a carbon sink, allowing more CO₂ to accumulate in the atmosphere
C. It causes denitrification bacteria to multiply
D. It accelerates the fast carbon cycle, trapping carbon in organisms
Show Answer & Explanation

Answer: (B) It reduces the ocean's role as a carbon sink, allowing more CO₂ to accumulate in the atmosphere

Explanation:
As ocean water warms, its reduced capacity to absorb CO₂ means less carbon is removed from the atmosphere, creating a feedback loop where rising temperatures prevent one of Earth's major carbon sinks from functioning effectively.

Question: Based on the chapter's discussion of how human land use affects local climate, which scenario best demonstrates how built-up urban areas create warmer conditions than surrounding rural regions?
A. Rural areas receive more direct solar radiation because they are at lower latitudes
B. Urban materials like concrete and asphalt absorb solar radiation and re-radiate heat, while rural forests stay cool through shade and transpiration
C. Cities are located farther from the equator, making them naturally warmer
D. Urban vegetation absorbs more CO₂ than forest vegetation
Show Answer & Explanation

Answer: (B) Urban materials like concrete and asphalt absorb solar radiation and re-radiate heat, while rural forests stay cool through shade and transpiration

Explanation:
The urban heat island effect occurs because cities have more built-up areas with materials that absorb and retain heat, whereas rural areas with forests stay cool through shade and plant transpiration, demonstrating how local land use alters climate.

Question: In the fast carbon cycle, plants convert atmospheric CO₂ into glucose using sunlight. Through which process does this conversion occur?
A. Respiration
B. Photosynthesis
C. Decomposition
D. Combustion
Show Answer & Explanation

Answer: (B) Photosynthesis

Explanation:
Photosynthesis is the process by which plants use sunlight to convert atmospheric CO₂ and water into glucose, which is the primary step of the fast carbon cycle occurring over days to years.

Question: If deforestation removes a large forest, which of the following chains of consequences would most directly affect the local water cycle and rainfall patterns?
A. • Decreased photosynthesis reduces glucose production • Animals lose food sources and migrate away • Biodiversity declines significantly • Soil becomes infertile
B. • Decreased photosynthesis and transpiration occurs • Less water vapour enters the atmosphere • Local rainfall declines • Groundwater recharge from infiltration is reduced
C. • Forest soils absorb less sunlight • Local temperatures become colder • More condensation occurs • Flooding increases
D. • Tree roots release stored carbon into the soil • Nitrogen fixation increases • Agricultural productivity improves • Sea levels decrease
Show Answer & Explanation

Answer: (B) • Decreased photosynthesis and transpiration occurs • Less water vapour enters the atmosphere • Local rainfall declines • Groundwater recharge from infiltration is reduced

Explanation:
Clearing forests reduces both photosynthesis and transpiration, decreasing water vapour in the atmosphere and local rainfall. Without tree roots to hold soil, infiltration decreases, reducing groundwater recharge and making agriculture difficult during dry periods.

Question: Which electromagnetic wavelengths make up approximately 99 per cent of the Sun's energy reaching Earth, and what are their primary roles in supporting life?
A. Gamma rays, X-rays and microwaves that provide energy for photosynthesis and atmospheric heating
B. Ultraviolet, visible and infrared radiation that drive photosynthesis, heating and the greenhouse effect
C. Radio waves and infrared radiation that penetrate the ozone layer and warm the surface directly
D. Microwaves and visible light that are absorbed equally by all surfaces regardless of albedo
Show Answer & Explanation

Answer: (B) Ultraviolet, visible and infrared radiation that drive photosynthesis, heating and the greenhouse effect

Explanation:
The chapter explicitly states that about 99 per cent of the Sun's energy reaching Earth falls within the ultraviolet, visible and infrared wavelengths. These three regions shape the Earth's climate and support life through distinct mechanisms: UV is mostly absorbed by the ozone layer, visible light provides energy for photosynthesis and partly warms land and water, and infrared radiation warms the surface which then re-radiates heat back into the atmosphere.

Question: How does the urban heat island effect demonstrate the principle that different surface materials absorb and retain solar energy differently?
A. Rural areas stay cooler because they have more concrete and asphalt, which reflect most incoming sunlight
B. Cities are warmer because built-up materials like steel, concrete and brick absorb solar radiation and re-radiate more heat than vegetation in rural areas
C. Urban temperatures rise because the denser population produces more body heat that accumulates in the atmosphere
D. Cities warm up because they receive more direct sunlight due to fewer clouds, while forests block sunlight through their canopy
Show Answer & Explanation

Answer: (B) Cities are warmer because built-up materials like steel, concrete and brick absorb solar radiation and re-radiate more heat than vegetation in rural areas

Explanation:
The chapter's discussion of the urban heat island effect explains that cities contain more built-up areas with materials that absorb solar radiation and retain heat through re-radiation. In contrast, rural areas and forests stay cooler through shade and plant transpiration. This directly illustrates how surface properties and composition determine how much energy is absorbed versus reflected.

Question: In the stratosphere, temperature increases with altitude even though less solar energy reaches this layer. What causes this counterintuitive pattern of warming?
A. The stratosphere is closer to the Sun than the troposphere, so it receives more direct radiation
B. Ozone in the stratosphere absorbs ultraviolet radiation, converting it into heat that warms this layer
C. Greenhouse gases like carbon dioxide accumulate at higher altitudes and trap more heat than at lower levels
D. The stratosphere contains more oxygen molecules that absorb and re-radiate infrared radiation from the Earth's surface
Show Answer & Explanation

Answer: (B) Ozone in the stratosphere absorbs ultraviolet radiation, converting it into heat that warms this layer

Explanation:
The chapter states that in the stratosphere, where the ozone layer is located, ozone absorbs UV rays and heats up the atmosphere, causing temperature to increase with height. This contrasts sharply with the troposphere below, where temperature decreases with altitude because that layer is heated primarily from the Earth's surface rather than directly by solar radiation.

Question: When comparing planetary winds formed between the equator and the poles, how does the Earth's rotation deflect these winds from their expected paths?
A. Winds are deflected toward the equator in both hemispheres because that region receives the most solar heating
B. Earth's rotation deflects winds rightward in the Northern Hemisphere and leftward in the Southern Hemisphere, creating curved paths instead of straight high-to-low pressure movement
C. Winds move directly from high pressure to low pressure zones without deflection because the Coriolis effect only affects ocean currents
D. Rotation causes winds to move in circles around pressure systems but does not change their overall direction from high to low pressure zones
Show Answer & Explanation

Answer: (B) Earth's rotation deflects winds rightward in the Northern Hemisphere and leftward in the Southern Hemisphere, creating curved paths instead of straight high-to-low pressure movement

Explanation:
• The chapter explains that Earth's rotation causes planetary winds to be deflected from their straight paths
• Winds deflect toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere
• This creates curved rather than direct paths between pressure regions, fundamentally altering global wind patterns and driving phenomena like the monsoons.

Question: How does the process of nitrification in the nitrogen cycle make atmospheric nitrogen available to plants, and which bacteria are responsible for this transformation?
A. Rhizobium bacteria convert atmospheric nitrogen gas into ammonia, which is then directly absorbed by plant roots
B. Nitrifying bacteria like Nitrosomonas and Nitrobacter convert ammonia into nitrite and then nitrate, forms that plants can assimilate from soil
C. Denitrifying bacteria break down nitrate molecules and release them back into the atmosphere for recycling by plants
D. Lightning fixes nitrogen oxides that plants directly absorb through their leaves during rainstorms
Show Answer & Explanation

Answer: (B) Nitrifying bacteria like Nitrosomonas and Nitrobacter convert ammonia into nitrite and then nitrate, forms that plants can assimilate from soil

Explanation:
The chapter describes nitrification as the process where bacteria like Nitrosomonas convert ammonia into nitrite, and Nitrobacter then converts nitrite into nitrate. These nitrogen compounds in the soil are the forms that plants actually assimilate, making this step essential for making atmospheric nitrogen accessible to the biosphere.

Question: Why does the chapter distinguish between the 'fast carbon cycle' and the 'slow carbon cycle,' and what would be the consequence if the slow cycle processes were completely halted?
A. The fast cycle operates over days to years through photosynthesis and respiration, while the slow cycle takes millions of years to form fossil fuels; halting the slow cycle would simply speed up the fast cycle without major impact
B. The fast cycle moves carbon between atmosphere and living organisms in days to years, while the slow cycle buries carbon in rocks and fossil fuels over millions of years; losing the slow cycle would disrupt long-term carbon storage and increase atmospheric CO₂
C. The slow cycle is more important than the fast cycle because fossil fuels contain more carbon than living organisms; stopping it would reduce available energy for human civilization
D. Both cycles operate at the same timescale but in different locations; the fast cycle occurs on land while the slow cycle occurs in oceans
Show Answer & Explanation

Answer: (B) The fast cycle moves carbon between atmosphere and living organisms in days to years, while the slow cycle buries carbon in rocks and fossil fuels over millions of years; losing the slow cycle would disrupt long-term carbon storage and increase atmospheric CO₂

Explanation:
The chapter explains that in the fast cycle (days to years), photosynthesis and respiration exchange carbon between organisms and the atmosphere, while in the slow cycle (millions of years), dead organisms are buried and converted to fossil fuels. This distinction highlights how the slow cycle acts as a long-term carbon reservoir. If halted, carbon would accumulate excessively in the fast cycle, increasing atmospheric CO₂ concentrations.

Question: When deforestation removes trees from a large forested region, which sequence of consequences would directly disrupt both the oxygen and carbon cycles?
A. Trees are cut down, reducing photosynthesis and transpiration, which decreases oxygen production and increases atmospheric CO₂; soil erosion follows because tree roots no longer hold soil together
B. Deforestation removes plants that require oxygen for respiration, immediately increasing oxygen levels in the atmosphere and reducing carbon dioxide
C. Cutting trees eliminates competitors for sunlight, allowing remaining plants to grow faster and produce more oxygen while absorbing excess atmospheric carbon dioxide
D. Forest clearing directly reduces rainfall by altering albedo, which prevents new trees from growing and gradually restores atmospheric carbon balance
Show Answer & Explanation

Answer: (A) Trees are cut down, reducing photosynthesis and transpiration, which decreases oxygen production and increases atmospheric CO₂; soil erosion follows because tree roots no longer hold soil together

Explanation:
• Reduced photosynthesis means less oxygen is produced and less atmospheric CO₂ is converted to organic matter
• Decreased transpiration contributes to reduced local rainfall, affecting regional hydrosphere and biosphere
• Loss of tree roots causes soil erosion, disrupting the geosphere and increasing runoff rather than infiltration
• The interconnected disruption of these cycles demonstrates how removing one organism affects multiple Earth spheres simultaneously.

Question: The chapter states that 71 per cent of Earth's global carbon is stored in oceans, yet the atmosphere holds only about 1 per cent. How does this imbalance relate to the current concern about rising atmospheric CO₂?
A. The ocean's carbon storage capacity is nearly full, so excess atmospheric CO₂ cannot be absorbed, causing rapid warming
B. Oceans regulate atmospheric CO₂ by absorbing it and forming carbonate and bicarbonate ions; if ocean absorption capacity weakens due to warming or oversaturation, atmospheric CO₂ accumulates
C. Most of the ocean's carbon is locked in shells and sediments that never interact with the atmosphere, so increasing atmospheric CO₂ does not affect ocean chemistry
D. The small atmospheric fraction of 1 per cent is actually sufficient to support all life processes, so rising CO₂ levels pose no threat to the carbon cycle
Show Answer & Explanation

Answer: (B) Oceans regulate atmospheric CO₂ by absorbing it and forming carbonate and bicarbonate ions; if ocean absorption capacity weakens due to warming or oversaturation, atmospheric CO₂ accumulates

Explanation:
The chapter identifies the ocean as a crucial carbon sink that absorbs atmospheric CO₂ to form carbonate and bicarbonate ions. However, it also notes that warmer ocean water reduces the ocean's capacity to absorb CO₂ effectively, and that excess atmospheric CO₂ from human activities can increase ocean acidity. This creates a feedback problem: as temperatures rise, the ocean's ability to absorb excess carbon weakens, allowing CO₂ to accumulate further in the atmosphere.

Question: How does the process of eutrophication in water bodies result from agricultural practices, and what is the biological consequence for aquatic organisms?
A. Farmers add nitrogen fertilisers to crops; excess nitrogen flows into rivers and lakes, triggering widespread algal growth that consumes oxygen and depletes it from the water, suffocating fish
B. Photosynthetic algae absorb excessive nitrogen from fertilisers and release toxic oxygen as a byproduct, poisoning fish directly rather than through oxygen depletion
C. Nitrogen fertilisers cause algae to release carbon dioxide into water bodies, which lowers pH and makes the environment unsuitable for fish survival
D. Agricultural runoff introduces phosphorus rather than nitrogen, stimulating algal blooms that block sunlight and prevent photosynthesis in aquatic plants
Show Answer & Explanation

Answer: (A) Farmers add nitrogen fertilisers to crops; excess nitrogen flows into rivers and lakes, triggering widespread algal growth that consumes oxygen and depletes it from the water, suffocating fish

Explanation:
The chapter defines eutrophication as the widespread growth of algae triggered by excessive nitrogen from agricultural fertilisers in water bodies. These algal blooms deplete oxygen as they decompose, killing fish and disrupting aquatic ecosystems. This demonstrates how human activities in one sphere (agriculture in the biosphere) can create cascading negative effects across multiple spheres by disrupting the nitrogen cycle.

Question: According to the chapter's discussion of climate change impacts on the water cycle, how do warmer atmospheric temperatures intensify both flooding in some regions and drought in others?
A. Warmer air holds more moisture, causing heavier rainfall in some areas and evaporating moisture faster in others, while melting glaciers raise sea levels uniformly across all coasts
B. A warmer atmosphere can hold more water vapour, leading to intensified rainfall and monsoons in some regions while other areas experience droughts as atmospheric moisture is preferentially concentrated in favoured zones
C. Rising temperatures cause the water cycle to slow down globally, reducing both evaporation and precipitation equally across all continents
D. Warmer oceans produce more clouds that reflect sunlight, cooling some regions while simultaneously trapping heat in others
Show Answer & Explanation

Answer: (B) A warmer atmosphere can hold more water vapour, leading to intensified rainfall and monsoons in some regions while other areas experience droughts as atmospheric moisture is preferentially concentrated in favoured zones

Explanation:
The chapter explains that climate change affects the water cycle by allowing a warmer atmosphere to hold more moisture, which intensifies monsoons and rainfall in some areas. Simultaneously, other regions experience drought conditions. Additionally, melting glaciers add water to rivers and raise sea levels, threatening coastal cities. This demonstrates how a single change in atmospheric temperature cascades through the hydrosphere and cryosphere, affecting different regions in opposite ways while linking multiple Earth spheres.

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