CBSE Class 9 Science Chapter 13: Earth as a System: Energy, Matter, and Life — Assertion & Reason
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The following Assertion and Reason questions are based on Chapter 13: Earth as a System: Energy, Matter, and Life from the NCERT Class 9 Science textbook. Each question has four options - read both the Assertion (A) and Reason (R) carefully before selecting your answer.
How to attempt Assertion & Reason questions:
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is NOT the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Assertion & Reason Questions
1
Assertion (A): A disturbance in one Earth sphere can produce changes in several other spheres.
Reason (R): Matter and energy move through interactions among the geosphere, hydrosphere, cryosphere, atmosphere, and biosphere.
Reason (R): Matter and energy move through interactions among the geosphere, hydrosphere, cryosphere, atmosphere, and biosphere.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Because the spheres exchange matter and energy, a change such as reduced snowfall can affect water, vegetation, and animals.
2
Assertion (A): Solar radiation is the principal external energy source driving processes at the Earth's surface.
Reason (R): Heat from the Earth's interior and chemical reactions also drive some movements of energy and matter.
Reason (R): Heat from the Earth's interior and chemical reactions also drive some movements of energy and matter.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both statements are correct, but the existence of additional energy sources does not explain why solar radiation is the principal external source.
3
Assertion (A): Electromagnetic radiation from the Sun can travel through the vacuum of space.
Reason (R): Sound waves can also travel through a vacuum because all waves behave like electromagnetic waves.
Reason (R): Sound waves can also travel through a vacuum because all waves behave like electromagnetic waves.
Answer: (c)
A is true, but R is false. Sound is a mechanical wave and needs a material medium.
4
Assertion (A): Gamma rays and radio waves together make up nearly all the solar energy reaching the Earth's surface.
Reason (R): About 99 per cent of incoming solar energy is concentrated in the ultraviolet, visible, and infrared ranges.
Reason (R): About 99 per cent of incoming solar energy is concentrated in the ultraviolet, visible, and infrared ranges.
Answer: (d)
A is false, but R is true. Gamma rays are mostly filtered high in the atmosphere, while radio waves contribute little heating energy.
5
Assertion (A): Uneven heating of the Earth's surface helps generate winds and ocean currents.
Reason (R): Temperature differences create pressure and density differences that set air and water in motion.
Reason (R): Temperature differences create pressure and density differences that set air and water in motion.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Movement from regions with different thermal and pressure conditions redistributes energy around the planet.
6
Assertion (A): Visible sunlight supplies energy for photosynthesis.
Reason (R): Infrared radiation contributes strongly to warming the Earth's surface.
Reason (R): Infrared radiation contributes strongly to warming the Earth's surface.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both statements describe roles of solar radiation, but infrared warming does not explain the photosynthetic role of visible light.
7
Assertion (A): The ozone layer absorbs much of the harmful short-wavelength ultraviolet radiation.
Reason (R): All ultraviolet radiation from the Sun reaches the Earth's surface without interacting with the atmosphere.
Reason (R): All ultraviolet radiation from the Sun reaches the Earth's surface without interacting with the atmosphere.
Answer: (c)
A is true, but R is false. Atmospheric ozone filters a substantial portion of short-wavelength UV radiation.
8
Assertion (A): The polar regions receive more concentrated solar energy per unit area than the equatorial region.
Reason (R): Because the Earth is spherical, sunlight strikes higher latitudes more obliquely and spreads over a larger area.
Reason (R): Because the Earth is spherical, sunlight strikes higher latitudes more obliquely and spreads over a larger area.
Answer: (d)
A is false, but R is true. Oblique rays make average insolation lower toward the poles.
9
Assertion (A): Greenhouse gases help keep the Earth warm enough to support life.
Reason (R): They absorb a portion of the infrared energy re-radiated by the Earth's surface.
Reason (R): They absorb a portion of the infrared energy re-radiated by the Earth's surface.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Absorption and re-emission of outgoing infrared energy slows heat loss to space.
10
Assertion (A): Most weather processes, including evaporation, condensation, and precipitation, occur in the troposphere.
Reason (R): The stratospheric ozone layer absorbs ultraviolet radiation.
Reason (R): The stratospheric ozone layer absorbs ultraviolet radiation.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both are true atmospheric facts, but ozone absorption does not explain why weather is concentrated in the troposphere.
11
Assertion (A): During the daytime, a sea breeze commonly blows from sea toward land.
Reason (R): This happens because water warms faster than land during the day.
Reason (R): This happens because water warms faster than land during the day.
Answer: (c)
A is true, but R is false. Land warms faster, the air above it rises, and cooler air moves inland from the sea.
12
Assertion (A): A mountain breeze moves warm air uphill from the valley during the night.
Reason (R): At night, mountain slopes cool and denser air flows downslope into the valley.
Reason (R): At night, mountain slopes cool and denser air flows downslope into the valley.
Answer: (d)
A is false, but R is true. The nighttime downslope flow is the mountain breeze; daytime upslope flow is the valley breeze.
13
Assertion (A): The water cycle transfers water among the atmosphere, land, water bodies, and living organisms.
Reason (R): Processes such as evaporation, condensation, precipitation, runoff, and transpiration connect these reservoirs.
Reason (R): Processes such as evaporation, condensation, precipitation, runoff, and transpiration connect these reservoirs.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Together these processes continually redistribute water across Earth spheres.
14
Assertion (A): Carbon continuously moves between living organisms and non-living reservoirs.
Reason (R): Photosynthesis is the main process that restores atmospheric oxygen used in respiration and combustion.
Reason (R): Photosynthesis is the main process that restores atmospheric oxygen used in respiration and combustion.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both statements are true, but the restoration of oxygen does not by itself explain the complete carbon cycle.
15
Assertion (A): Atmospheric oxygen is consumed in respiration, combustion, and oxide formation.
Reason (R): Burning fossil fuels is the principal natural process that restores oxygen to the atmosphere.
Reason (R): Burning fossil fuels is the principal natural process that restores oxygen to the atmosphere.
Answer: (c)
A is true, but R is false. Photosynthesis, not fossil-fuel combustion, mainly replenishes atmospheric oxygen.
16
Assertion (A): Warmer ocean water always increases the ocean's ability to absorb carbon dioxide as a carbon sink.
Reason (R): As ocean water warms, its capacity to absorb and retain carbon dioxide can decrease.
Reason (R): As ocean water warms, its capacity to absorb and retain carbon dioxide can decrease.
Answer: (d)
A is false, but R is true. Warming can weaken the ocean carbon sink even while excess atmospheric carbon dioxide also increases ocean uptake and acidification.
17
Assertion (A): Most organisms cannot use atmospheric nitrogen gas directly.
Reason (R): Nitrogen-fixing microorganisms convert nitrogen into compounds that can enter soil and food webs.
Reason (R): Nitrogen-fixing microorganisms convert nitrogen into compounds that can enter soil and food webs.
Answer: (a)
Both A and R are true, and R is the correct explanation of A. Fixation makes nitrogen biologically available for building substances such as proteins and nucleic acids.
18
Assertion (A): Burning fossil fuels and deforestation increase the concentration of atmospheric carbon dioxide.
Reason (R): Excess fertiliser runoff can produce algal blooms and eutrophication in water bodies.
Reason (R): Excess fertiliser runoff can produce algal blooms and eutrophication in water bodies.
Answer: (b)
Both A and R are true, but R is NOT the correct explanation of A. Both are human impacts on Earth cycles, but fertiliser-driven eutrophication does not explain the rise in atmospheric carbon dioxide.
19
Assertion (A): Energy conservation, renewable energy, tree planting, and reduced waste can help restore environmental balance.
Reason (R): Actions by individuals and communities have no influence on resource use or greenhouse-gas emissions.
Reason (R): Actions by individuals and communities have no influence on resource use or greenhouse-gas emissions.
Answer: (c)
A is true, but R is false. Collective changes in consumption, energy use, reuse, and recycling can reduce environmental pressure.
20
Assertion (A): Eutrophication increases dissolved oxygen and permanently improves fish survival in lakes.
Reason (R): Dense algal growth followed by decomposition can deplete oxygen and kill aquatic animals.
Reason (R): Dense algal growth followed by decomposition can deplete oxygen and kill aquatic animals.
Answer: (d)
A is false, but R is true. Nutrient enrichment often lowers available oxygen rather than improving it.
❓ Frequently Asked Questions
What is covered in CBSE Class 9 Science Chapter 13 Earth as a System: Energy, Matter, and Life?
This chapter covers all key topics from Earth as a System: Energy, Matter, and Life as per CBSE 2026-27 syllabus.
Is this Assertion & Reason useful for CBSE board exams?
Yes, designed for CBSE Class 9 board exam preparation covering the complete syllabus.
Are these CBSE Class 9 Science Assertion & Reason updated for 2026-27?
Yes, all content at eBookPublisher is updated as per the latest 2026-27 CBSE syllabus.
How many chapters are in CBSE Class 9 Science?
All chapters of CBSE Class 9 Science are covered at eBookPublisher with free Assertion & Reason for each chapter.
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