DAV Class 6 SST Chapter 5 Question Answer The Realms of the Earth

Looking for the most authentic, 100% textbook-grounded DAV Class 6 Social Science Chapter 5 Solutions: The Realms of the Earth? Based strictly on the prescribed DAV CMC textbook We and Our World, this master guide provides complete, detailed answers for Section A (Tick the correct option with detailed reasons), Section B (Fill in the blanks), Section C (Match the following table), Section D (Short Answer Questions), Section E (Detailed Long Answer Questions with structural headings), Value-Based Questions (VBQ), HOTS, multi-column comparison tables (Mountains vs Plateaus vs Plains, Layers of Atmosphere), and authentic DAV Board Examination Previous Years’ Questions (2018-2024) with official marking schemes.

Section A: Tick (✓) the Correct Option

1. Which one of the following is an old mountain?
(a) The Himalayas
(b) The Alps
(c) The Andes
(d) The Aravalli Range
Answer: (d) The Aravalli Range
Detailed Justification: The Aravalli Range in northwestern India is one of the oldest fold mountain systems in the world, formed hundreds of millions of years ago and significantly eroded over geological eras. In contrast, the Himalayas, Alps, and Andes are young fold mountains formed relatively recently with sharp, pointed peaks.

2. How much surface of the earth is covered by oceans?
(a) 29%
(b) 50%
(c) 71%
(d) 97%
Answer: (c) 71%
Detailed Justification: Approximately 71% of the Earth’s total surface area is submerged under oceans and water bodies (the Hydrosphere), while the remaining 29% constitutes land masses and continents (the Lithosphere). This abundant water presence gives Earth its nickname, the ‘Blue Planet’.

3. The largest ocean of the world is:
(a) Atlantic Ocean
(b) Indian Ocean
(c) Pacific Ocean
(d) Arctic Ocean
Answer: (c) Pacific Ocean
Detailed Justification: The Pacific Ocean is the largest and deepest ocean on Earth, spreading over an area greater than all continents combined (occupying about one-third of the planet’s total surface). It also houses the deepest oceanic trench on Earth, the Mariana Trench (approx. 11,034 metres deep).

4. Which continent is the most advanced and economically developed continent?
(a) Asia
(b) Africa
(c) Europe
(d) South America
Answer: (c) Europe
Detailed Justification: Europe is widely regarded as the most economically advanced and industrialized continent due to its early Industrial Revolution, high literacy rates, modern infrastructure, advanced technology, and well-developed trade networks.

5. Which one of the following gases has the largest volume in the atmosphere?
(a) Oxygen
(b) Carbon dioxide
(c) Nitrogen
(d) Hydrogen
Answer: (c) Nitrogen
Detailed Justification: Nitrogen is the most abundant gas in Earth’s atmosphere, accounting for approximately 78% of the total volume of dry air. Oxygen makes up about 21%, while all other gases combined (argon, carbon dioxide, helium, hydrogen, etc.) account for the remaining 1%.

Section B: Fill in the Blanks

1. Biosphere is a narrow belt or zone of the earth where all forms of life exist.
2. An envelope of the air surrounding the earth is called atmosphere.
3. Lithosphere is the upper surface of the earth consisting of rocks.
4. A highly elevated land from the surroundings with very steep slopes is known as mountains.
5. An upland with rugged surface is called plateau (often described as tableland).

Section C: Match the Following

Column A (Geographical Feature)	Column B (Correct Match)	Detailed Scientific Significance
1. It separates Europe and Asia	(e) Ural mountain and Ural river	The Ural Mountains and the Ural River form the traditional physical boundary separating European Russia from Asian Russia.
2. It joins North America with South America	(c) Isthmus of Panama	An isthmus is a narrow strip of land connecting two larger landmasses; the Isthmus of Panama connects North and South America.
3. The largest continent of the world	(a) Asia	Asia covers nearly one-third of the total land area of the globe and contains over 60% of the world’s human population.
4. It helps in burning	(b) Oxygen	Oxygen is an active supporter of combustion, necessary for all burning processes and cellular respiration in living organisms.
5. Continent in the Southern Hemisphere	(d) Antarctica	Antarctica lies entirely centered around the South Pole in the Southern Hemisphere, permanently buried under an immense sheet of ice.

Section D: Answer the Following Questions in Brief

Question 1: Name the four realms of the Earth.
Answer:
The four interconnected realms (spheres) of the Earth are:

1. Lithosphere: The solid outer crust and rock surface of the Earth, including landforms and soil.
2. Hydrosphere: The total water component of the Earth, including oceans, seas, rivers, lakes, glaciers, and groundwater (covering 71% of Earth’s surface).
3. Atmosphere: The gaseous envelope of air surrounding the planet, held in place by Earth’s gravity.
4. Biosphere: The narrow zone of contact where lithosphere, hydrosphere, and atmosphere interact to support life.

Question 2: Which four gases constitute only one per cent of the total volume of the atmosphere?
Answer:
The four prominent gases that, together with minor trace gases, make up only 1% of the total atmospheric volume are:

• Argon (Ar): Approx. 0.93%
• Carbon dioxide (CO₂): Approx. 0.03% to 0.04%
• Hydrogen (H₂): Trace amounts
• Helium (He): Trace amounts (along with ozone, neon, krypton, and xenon).

Question 3: Which continent is not inhabited by the people and why?
Answer:
Antarctica is the continent that is not permanently inhabited by humans.
Reasons:

• Extreme Cold: It is the coldest, windiest, and driest continent on Earth, where winter temperatures plunge below -80°C.
• Permanent Ice Cover: More than 98% of its landmass is permanently buried under an ice cap with an average thickness of 1.6 km.
• Lack of Vegetation: Extreme frost prevents soil formation, agricultural cultivation, and plant growth, supporting only visiting scientists in specialized research stations (like India’s Dakshin Gangotri, Maitri, and Bharati).

Question 4: Why is Earth known as a unique planet?
Answer:
Earth is known as a unique planet in the entire Solar System because it is the only celestial body known to support life.
This uniqueness is due to three ideal conditions:

1. Optimum Temperature: Earth’s moderate distance from the Sun (approx. 150 million km) prevents it from being too scorchingly hot like Mercury or bitterly freezing like Neptune.
2. Presence of Liquid Water: Liquid water is abundant on Earth, which is an indispensable solvent and medium for all biological life.
3. Life-Supporting Atmosphere: An oxygen-rich breathable atmosphere protected by an ozone layer that blocks harmful ultraviolet (UV) solar radiation.

Question 5: Name three major landforms on the land surface.
Answer:
The three major landforms found on the Earth’s lithospheric surface are:

1. Mountains: Highly elevated landforms with steep slopes and conical peaks rising sharply above surrounding terrain.
2. Plateaus: Elevated flat-topped tablelands rising abruptly above surrounding areas, often characterized by rugged rocky surfaces.
3. Plains: Low-lying, extensive flat or gently undulating lands, mostly formed by alluvial river deposits.

Section E: Answer the Following Questions in Detail

Question 1: What are plains? Explain briefly the formation of plains.
Answer:
Definition of Plains: A plain is an extensive stretch of low-lying, flat or gently rolling land, generally not more than 200 metres above mean sea level.

Process of Formation:

1. Origin in Mountains: Most of the world’s fertile plains have been formed by the continuous geological action of rivers and their tributaries originating from high snow-capped mountains.
2. Erosion and Transport: As turbulent rivers flow down steep mountain slopes, they relentlessly erode rocks and valley walls, carrying immense volumes of silt, sand, clay, gravel, and organic sediments (alluvium).
3. Deposition in Lowlands: Upon reaching gentler, flat gradients, river velocities decrease sharply. The rivers drop and deposit their heavy sedimentary loads across wide floodplains and valleys over millions of years.
4. Alluvial Enrichment: These continuous sedimentary deposits form thick layers of mineral-rich, highly fertile alluvial soil, giving rise to expansive plains such as the Northern Plains of India (formed by the Indus, Ganga, and Brahmaputra) and the Hwang-Ho Plain in China.

Question 2: Give a brief account of the plateaus of the world.
Answer:
A plateau is an elevated upland with a relatively flat, broad top and steep sides, often termed a tableland. Plateaus cover nearly 40% of the Earth’s total land surface and typically have an average height of around 600 metres above sea level.

Key Global Plateaus:

1. The Tibetan Plateau: Known as the ‘Roof of the World’, it is the highest and largest plateau on Earth, with an elevation exceeding 4,500 to 5,000 metres above sea level.
2. The Deccan Plateau (India): A massive triangular volcanic plateau bounded by the Western and Eastern Ghats, composed of fertile black cotton soil (basaltic lava).
3. The Arabian Plateau: An expansive dry desert plateau rich in petroleum and hydrocarbon reserves.
4. The Brazilian Plateau: A mineral-rich highland covering vast territories in eastern South America.

Economic Significance: Plateaus are storehouses of valuable mineral deposits (iron ore, coal, gold, manganese, and diamonds) and feature steep waterfalls that generate hydroelectric power.

Question 3: Name the two main gases of the atmosphere. Write the significance of each.
Answer:
The two main gases constituting approximately 99% of the Earth’s atmosphere are Nitrogen and Oxygen.

1. Significance of Nitrogen (78% of Atmosphere):

• Dilutes Oxygen: Nitrogen is chemically inert. It dilutes the highly reactive oxygen gas, preventing rapid, uncontrollable fires and combustion at the Earth’s surface.
• Essential for Living Organisms: Nitrogen is an essential constituent of amino acids and proteins, vital for the survival and growth of plants and animals (fixed by soil bacteria like Rhizobium).
• Atmospheric Pressure: Because of its high volume, nitrogen exerts the necessary atmospheric pressure to sustain weather cycles and human respiration.

2. Significance of Oxygen (21% of Atmosphere):

• Vital for Respiration: Oxygen is the ‘breath of life’, essential for cellular respiration in all aerobic organisms, including humans, animals, and plants.
• Supports Combustion: No fuel (wood, coal, gas) can burn without oxygen, making it fundamental for cooking, industrial energy, and heat generation.

Question 4: What is meant by hydrosphere? Briefly explain the importance of the hydrosphere.
Answer:
Definition: The Hydrosphere comprises the entire water domain of the Earth, including all water found on the surface (oceans, seas, lakes, rivers), beneath the ground (groundwater, aquifers), and in the atmosphere (water vapor, clouds). It covers approximately 71% of the planet’s surface.

Importance of the Hydrosphere:

1. The Hydrological (Water) Cycle: The hydrosphere drives evaporation, condensation, and precipitation, ensuring fresh rain and snow replenish rivers, reservoirs, and agricultural crops.
2. Moderating Global Climate: Oceans absorb enormous amounts of solar radiation and circulate heat across the globe via marine currents, moderating extreme temperature variations between equatorial and polar zones.
3. Rich Source of Food & Minerals: Oceans provide billions of people with protein through fisheries and contain vast reserves of common salt, petroleum, natural gas, and precious minerals.
4. International Maritime Trade: Ocean waterways form the cheapest and most efficient transport corridors for international trade and shipping.

Question 5: How are human activities responsible for causing ecological imbalance?
Answer:
Human activities have exerted unprecedented pressure on all four realms of the Earth, severely disrupting the delicate balance of ecosystems.

Key Anthropogenic Causes of Ecological Imbalance:

1. Rampant Deforestation: Indiscriminate felling of trees for agriculture, urban housing, and timber destroys wildlife habitats, triggers severe soil erosion, reduces rainfall, and increases atmospheric carbon dioxide.
2. Industrial and Vehicular Pollution: The emission of toxic greenhouse gases (CO₂, SO₂, NO_x) causes global warming, melting polar ice caps, and triggering acid rain.
3. Water Contamination: Dumping untreated industrial effluents, toxic chemical waste, and domestic sewage into rivers and oceans destroys aquatic ecosystems, causing eutrophication and coral reef bleaching.
4. Overexploitation of Natural Resources: Uncontrolled mining, groundwater over-extraction, and poaching have pushed countless plant and animal species to the verge of extinction.

Remedy: Humanity must immediately embrace sustainable development, afforestation, conservation of biodiversity, and renewable energy to restore environmental harmony.

Core Landforms Comparison Table

Feature / Parameter	Mountains	Plateaus	Plains
Topography	High elevation with steep slopes and conical peaks.	Elevated tableland with flat/rugged top and steep sides.	Low-lying flat or gently rolling terrain.
Average Elevation	Typically above 900 to 1,000 metres.	Around 300 to 600 metres (Tibet > 4,500m).	Below 200 metres above sea level.
Soil & Fertility	Thin, rocky, unfertile soil prone to landslides.	Fertile black lava soil in volcanic plateaus; rocky otherwise.	Deep, extremely fertile alluvial soil.
Population Density	Sparsely populated due to harsh terrain and cold climate.	Moderately populated; concentrated near mining centers.	Densely populated; ideal for settlements and farming.
Economic Importance	Source of perennial rivers, forests, and tourism.	Rich in minerals (coal, iron ore) and hydro power.	Granary of the world; intensive agriculture and industry.
Examples	Himalayas, Alps, Rockies, Andes.	Deccan Plateau, Tibetan Plateau, Brazilian Plateau.	Indo-Gangetic Plain, Mississippi Plain.

Value-Based Questions (VBQ)

Question: The Biosphere represents a narrow, fragile zone where the lithosphere, hydrosphere, and atmosphere interact harmoniously to support life. Human greed has disrupted this harmony. What core environmental values and civic responsibilities must students cultivate to protect our Mother Earth?
Answer:
Students should cultivate the following ethical values and responsibilities:

1. Interconnectedness and Respect for Nature: Understanding that harming any single sphere (such as polluting a river or cutting down a forest) directly destabilizes the entire web of life, including human health.
2. Principle of Sustainable Living: Practicing the 4 R’s – Reduce, Reuse, Recycle, and Refuse – in daily life to conserve natural water, paper, and electrical energy.
3. Active Participation in Green Initiatives: Planting native trees, eliminating single-use plastics, and participating in cleanliness drives in schools and communities.

Higher Order Thinking Skills (HOTS)

Question 1: Why are the Northern Plains of India known as the ‘Granary of India’, while the Himalayan Mountains have very little agricultural cultivation?
Answer:
The sharp agricultural contrast is due to distinct geographical factors:

• Topography: The Northern Plains are flat, enabling intensive canal irrigation, tractor mechanization, and transport infrastructure. Mountains have steep, rugged slopes where only small terrace farming is possible.
• Soil Thickness: Plains possess deep, continuously replenished fertile alluvial soils deposited by the Ganga, Brahmaputra, and Indus rivers, whereas mountain slopes suffer severe erosion and retain only thin, rocky soils.
• Climate: Plains have favorable warm growing seasons, while high mountain altitudes suffer harsh frost, freezing winters, and short growing seasons.

Question 2: What would happen to life on Earth if the ozone layer in the atmosphere disappeared?
Answer:
The ozone layer (situated in the stratosphere) acts as a giant planetary sunscreen absorbing lethal solar ultraviolet (UV-B and UV-C) rays. If it disappeared:

• Humans and animals would suffer widespread skin cancers, cataracts, and severe immune system failure.
• Marine phytoplankton – the foundation of ocean food chains producing over 50% of the world’s oxygen – would be destroyed.
• Terrestrial plant photosynthesis would be severely impaired, collapsing agricultural food production and causing planetary famine.

Authentic DAV Board Examination Previous Years’ Questions (2018-2024)

Q1 [DAV Mid-Term Exam 2023, 3 Marks]: Differentiate between an Isthmus and a Strait with suitable examples.
Official Answer & Marking Scheme:
1. Isthmus [1.5 Marks]: A narrow strip of land connecting two larger landmasses and separating two bodies of water. Example: Isthmus of Panama connecting North and South America.
2. Strait [1.5 Marks]: A narrow passage of water connecting two large water bodies (such as seas or oceans). Example: Palk Strait connecting the Bay of Bengal with the Gulf of Mannar (separating India and Sri Lanka).

Q2 [DAV Annual Exam 2022, 2 Marks]: Why is the atmosphere essential for life on Earth? Mention two reasons.
Official Answer & Marking Scheme:
1. Life-Giving Gases [1 Mark]: It provides oxygen for animal and human respiration, and carbon dioxide for plant photosynthesis.
2. Thermal Blanket & Shield [1 Mark]: It retains heat at night like a blanket to prevent extreme freezing and protects Earth from burning meteorites through friction.

Q3 [DAV Annual Exam 2020, 3 Marks]: Explain the significance of the Deccan Plateau for India’s economy.
Official Answer & Marking Scheme:
1. Mineral Wealth [1 Mark]: It is exceptionally rich in minerals including coal, iron ore, bauxite, and mica.
2. Cotton Cultivation [1 Mark]: Its northwestern part (Deccan Trap) is covered with fertile black soil (regur), ideal for cotton cultivation.
3. Hydroelectricity [1 Mark]: Rivers flowing across its steep stepped edges form waterfalls (e.g., Jog Falls) utilized for generating hydroelectric power.

DAV Class 6 Social Science: Complete Chapter Solutions Navigation

Access 100% textbook-authentic solutions for all 24 chapters of DAV Class 6 Social Science (We and Our World):

Unit	Chapter Number & Title	Direct Solution Link
Geography (The Earth: Our Habitat)	Ch 1: The Planet Earth and the Solar System	Read Ch 1 Solutions →
	Ch 2: Representation of the Earth	Read Ch 2 Solutions →
	Ch 3: Locating Places on the Earth	Read Ch 3 Solutions →
	Ch 4: The Motions of the Earth	Read Ch 4 Solutions →
	Ch 5: The Realms of the Earth	Current Chapter
	Ch 6: India – My Motherland	Read Ch 6 Solutions →
	Ch 7: India – The Land of Monsoon Climate	Read Ch 7 Solutions →
All 24 Chapters Master Solutions Index		DAV Class 6 SST Solutions Hub →