Earth as a System: Energy, Matter, and Life - Chapter 13 Exploration

Question 1
Choose the most appropriate option to describe the role of biogeochemical cycles in an ecosystem. (i) To provide food directly to all organisms. (ii) To recycle essential nutrients between biotic and abiotic components. (iii) To create new elements for use by living things. (iv) To remove pollutants and toxins from the organism.
View Answer
Hide Answer
Answer: (ii) To recycle essential nutrients between biotic and abiotic components
Biogeochemical cycles move nutrients like carbon, nitrogen and oxygen between living organisms and the non-living environment, keeping them available.
They do not directly feed all organisms, create new elements, or simply remove toxins.
Option
Is this the role of a biogeochemical cycle?
(i) To provide food directly to all organisms
✗ No — food is made by producers through photosynthesis; that is not what a cycle does.
(ii) To recycle essential nutrients between biotic and abiotic components
✓ Yes — this is the definition: the cyclic movement of matter between the living and non-living parts of the Earth.
(iii) To create new elements for use by living things
✗ No — elements are never created. The same carbon and nitrogen atoms move round and round.
(iv) To remove pollutants and toxins from the organism
✗ No — that is excretion, a body process, not an Earth-system cycle.
Back to: 13.3 Biogeochemical Cycles

Question 2
Which of the following is primarily responsible for warming of the Earth? (i) Solar radiation is immediately absorbed by carbon dioxide, which then releases it as heat. (ii) The atmosphere’s tiny particles absorb incoming solar radiation, which directly heats the Earth. (iii) The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases. (iv) The Earth’s environment is heated only by the solar radiation reflected by the clouds.
View Answer
Hide Answer
Answer: (iii) The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases
The surface absorbs sunlight and re-radiates it as infrared; greenhouse gases (CO₂, CH₄, water vapour) trap this outgoing heat.
This trapped heat, not direct absorption by particles or reflected light, mainly warms the Earth.
Option
Is this how the Earth is warmed?
(i) Solar radiation is immediately absorbed by carbon dioxide, which then releases it as heat
✗ No — CO
2
does not absorb the incoming sunlight; it absorbs the outgoing infrared re-radiated by the surface.
(ii) The atmosphere’s tiny particles absorb incoming solar radiation, which directly heats the Earth
✗ No — particles scatter and absorb a little, but this is not the main warming pathway.
(iii) The Earth’s surface absorbs solar radiation, which is then re-radiated and trapped by greenhouse gases
✓ Yes — surface absorbs sunlight, re-radiates it as infrared, and greenhouse gases trap it. This is the greenhouse effect.
(iv) The Earth’s environment is heated only by the solar radiation reflected by the clouds
✗ No — reflected radiation leaves the system; it does not warm the Earth.
Back to: 13.1.3 Role of the atmosphere

Question 3
Explain how climate change affects the water cycle. Illustrate with examples.
View Answer
Hide Answer
A warmer atmosphere holds more moisture, causing heavier rains and intensified monsoons in some places and droughts in others.
Melting glaciers add water to rivers and raise sea levels, while sudden intense rainfall causes run off and erosion and reduces groundwater recharge, making agriculture harder.
Climate and Water
Warmer air holds more
moisture
Heavier rains and droughts
result
Glaciers melt and seas rise
Back to: 13.3.1 Water cycle

Question 4
Describe how albedo affects the Earth’s surface temperature and its climate.
View Answer
Hide Answer
Albedo is the fraction of sunlight a surface reflects; high-albedo surfaces (snow, ice) reflect most light and stay cool, keeping polar regions cold.
Low-albedo surfaces (black soil, ocean) absorb more sunlight and warm up, so changing albedo (e.g. by melting ice or deforestation) can shift regional and global temperatures.
Albedo and Climate
High albedo
Snow and ice
reflect light
Low albedo
Dark surfaces
absorb
High-albedo surfaces stay cool while
low- albedo surfaces absorb heat, so
albedo shapes the climate.
Back to: 13.1.1 Interaction of solar radiation on the Earth’s surface

Question 5
How are mountain and valley breezes formed? Suppose there are two mountains, one covered with grass and another covered with barren rocks; would the temperature of the two mountain breezes be different? If so, how?
View Answer
Hide Answer
By day, sun-heated slopes warm the air, which rises, drawing a valley breeze up the slopes; by night the cooled slopes send a mountain breeze down.
Yes — the barren-rock mountain heats and cools faster than the grass-covered one, so its slopes reach higher and lower temperatures, making its breezes stronger and more extreme.
Slope Breezes
Slopes heat by day and cool
by night
Air rises, then later sinks
Barren rock heats faster
than grass
So its breezes are stronger
Back to: 13.2.1 Local winds

Question 6
You have witnessed weather phenomena, such as winds, storms, rainfall, etc. Which atmospheric layer is mainly responsible for such phenomena and what is the primary reason for its occurrence?
View Answer
Hide Answer
The
troposphere
is mainly responsible for weather like winds, storms and rainfall.
It is heated from the Earth’s surface, so temperature falls with height and warm air rises — this vertical mixing drives winds and storms.
Weather Layer
Weather forms in the
troposphere
It is heated from the surface
Rising warm air drives the
storms
Back to: 13.1.3 Role of the atmosphere

Question 7
Explain the processes involved in the nitrogen cycle. How would life on Earth be affected if nitrogen were not cycled?
View Answer
Hide Answer
Nitrogen fixation (bacteria/lightning convert N₂ to ammonia), nitrification (ammonia to nitrite to nitrate), assimilation by plants, ammonification (decomposers return ammonia) and denitrification (nitrate back to N₂).
Without cycling, soil nitrogen would run out, so plants could not make proteins and nucleic acids, and the whole food chain would collapse.
Nitrogen Cycle
Fixation makes ammonia
Nitrification makes nitrate
Denitrification returns
nitrogen gas
Without it, life would fail
Back to: 13.3.3 Nitrogen cycle

Question 8
What are the impacts of deforestation on the Earth’s oxygen and carbon cycles? What are the other consequences of deforestation?
View Answer
Hide Answer
Deforestation reduces photosynthesis, so less CO₂ is absorbed and less O₂ is released — disrupting both the oxygen and carbon cycles.
Other consequences include less transpiration and rainfall, altered albedo, increased soil erosion and loss of habitats and biodiversity.
Deforestation
Fewer trees means less
photosynthesis
Less carbon dioxide
absorbed, less oxygen made
It also brings erosion and
habitat loss
Back to: 13.4 Human Impact on Earth’s Processes

Question 9
Explain with suitable diagram the path that carbon takes to go back to the atmosphere. You may start from plants using CO₂ from the atmosphere.
View Answer
Hide Answer
Plants take in CO₂ by photosynthesis; through respiration in plants and animals CO₂ is returned to the air.
When organisms die, decomposition releases CO₂; and burning fossil fuels formed from ancient organisms releases CO₂ back to the atmosphere — completing the path.
Carbon's Path Back
Plants take in carbon
dioxide
Respiration and decay
release it
Burning fuels returns it to
the air
Back to: 13.3.2 Carbon cycle

Question 10
Why is an excess of CO₂ in the atmosphere considered undesirable even though it is required by plants?
View Answer
Hide Answer
Although plants need CO₂ for photosynthesis, excess CO₂ strengthens the greenhouse effect, causing global warming, melting ice and rising seas.
It also acidifies the oceans, threatening plankton and coral — so the balance, not just the presence, of CO₂ is critical.
Excess Carbon Dioxide
Plants do need some
carbon dioxide
But excess traps too much
heat
It warms and acidifies the
planet
Back to: 13.3.2 Carbon cycle

Question 11
How is heat lost from the surface of the Earth? What is its significance?
View Answer
Hide Answer
The Earth’s surface absorbs sunlight and re-radiates it as
infrared
heat back towards space.
Greenhouse gases trap part of this outgoing heat — keeping the Earth warm enough for life; the balance between incoming and outgoing heat sets the planet’s temperature.
Losing Heat
The surface re-radiates
infrared
Greenhouse gases trap
some of it
This keeps the Earth warm
enough
Back to: 13.1.3 Role of the atmosphere

Question 12
If the Earth were a flat disc instead of a sphere, how would the patterns of solar radiation and temperature be different?
View Answer
Hide Answer
On a flat disc facing the Sun, the rays would strike almost the same angle everywhere, so heating would be far more even across the surface.
The strong equator-to-pole temperature difference (caused by the curved surface) would largely vanish, changing wind and climate patterns.
Sphere vs Flat Disc
A sphere
Rays vary with
latitude
A flat disc
Rays hit evenly
On a sphere heating is uneven, but a
flat disc facing the Sun would heat
almost evenly everywhere.
Back to: 13.1.2 Latitude and Earth’s shape

Question 13
Suppose there is a rise in atmospheric temperature on Earth. How would this affect the cryosphere, hydrosphere and biosphere?
View Answer
Hide Answer
Cryosphere:
glaciers and polar ice melt faster.
Hydrosphere:
sea levels rise and rainfall patterns become more variable.
Biosphere:
habitats are lost and ecosystems are disturbed — showing how a change in one sphere ripples through the others.
A Warmer Earth
Cryosphere - the ice melts
Hydrosphere - the seas rise
Biosphere - habitats are lost
Back to: What We Will Cover

Question 14
Explain how the Earth’s atmosphere helps in maintaining a suitable temperature for life to survive on the Earth.
View Answer
Hide Answer
The atmosphere absorbs harmful incoming UV (ozone layer) and lets useful radiation through.
It also traps part of the outgoing infrared heat with greenhouse gases — without this the Earth would be too cold, so the atmosphere keeps temperatures suitable for life.
Atmosphere and Life
Filters
Blocks harmful
UV rays
Traps
Holds outgoing
heat
The atmosphere blocks harmful UV and
traps outgoing heat, keeping
temperatures suitable for life.
Back to: 13.1.3 Role of the atmosphere

Question 15
Describe the interrelationship between different spheres of the Earth. Illustrate with example how these spheres function in a delicate balance.
View Answer
Hide Answer
The geosphere, hydrosphere, cryosphere, atmosphere and biosphere constantly exchange energy and matter, so a change in one affects the others.
For example, less snowfall (cryosphere) lowers lake water (hydrosphere) and reduces grass for animals (biosphere); warmer air (atmosphere) melts glaciers and threatens coastal life — a delicate balance.
Linked Spheres
The five spheres exchange
energy and matter
A change in one affects the
others
Less snow lowers lakes and
grass
Back to: What We Will Cover

Project 1
Consider two hypothetical Earth-sized planets that have an atmosphere. Assume that one planet is entirely covered by oceans and the other is entirely by land. Knowing that the Sun heats the equator more than the poles, how would the wind patterns on these planets compare with the wind systems we observe on Earth, with its combination of land and sea?
View Sample Response
Hide Sample Response
On the all-ocean planet, heating would be smooth and winds simple and steady; on the all-land planet, land heats and cools quickly, giving sharper temperature swings and gustier winds. Earth’s mix of land and sea creates monsoons, land and sea breezes and more complex, seasonal wind patterns than either extreme.

Project 2
Choose any one meal you ate recently (for example, roti and dal, rice and sambar, idli and chutney). For each main item, explain: (i) how the carbon in it originally came from carbon dioxide in the air through photosynthesis, and (ii) how the nitrogen in it likely came from the atmosphere into the soil (by bacteria or the Haber-Bosch process and fertilisers) and then into the plant. Also list other human activities in producing or cooking the meal that add extra carbon dioxide or nitrogen.
View Sample Response
Hide Sample Response
Trace each grain and pulse back to a plant that fixed atmospheric CO₂ into sugars and starch by photosynthesis, and to soil nitrogen supplied by Rhizobium in pulse roots or by Haber-Bosch fertilisers. Then list carbon- and nitrogen-adding steps like transport, milling, cooking on gas and fertiliser use.

Project 3
Using data from the India Meteorological Department (IMD) or newspaper records, find the average monsoon rainfall (June–September, or the local season) for your city or district for 5 years during two decades, such as the 1980s and 2020s. Note any trend (increasing, decreasing, or the total number of days with heavy rain over 50 mm). How can this be connected to warmer Arabian Sea temperatures or changes in land use (forests to farms to cities) as discussed in the chapter?
View Sample Response
Hide Sample Response
Tabulate the five-year averages for each decade and compare them. Note whether total rainfall or the number of heavy-rain days has risen or fallen, then link any trend to warmer seas (more evaporation and intense bursts) or land-use change (urban heat and altered albedo affecting local rainfall).
🔑 The Quest Continues…
New tools are letting scientists observe the planet in real time and uncover hidden links between climate, ecosystems and human activity. What new discoveries will these tools reveal about the changing Earth, and how will they deepen our understanding of global warming and climate change?