DAV Board Class 7 Social Science (We and Our World) | 100% Authentic Textbook Solutions

DAV Class 7 SST Chapter 6 Life on the Earth Solutions

Get complete, 100% authentic textbook solutions for DAV Class 7 Social Science (We and Our World – Geography) Chapter 6: Life on the Earth. This comprehensive study guide features detailed chapter summaries and core concepts (Biosphere, Ecosystem components, Producers/Food Factories, Consumers, Decomposers, Food Chain, Global Vegetation Belts: Tropical Evergreen & Deciduous Forests, Tropical & Temperate Grasslands, Hot & Cold Deserts, Coniferous/Taiga Forests, Animal Adaptations, Ecological Imbalance, and Wildlife Conservation), key scientific definitions, complete textbook exercise solutions (Section A: MCQs, Section B: Fill in the Blanks, Section C: True or False, Section D: Short Answer Questions, Section E: Detailed Explanations), Value Based Questions (VBQ on Asiatic Lions of Gir), Higher Order Thinking Skills (HOTS), Map Work, and project activities strictly adhering to the DAV Education Board curriculum.

1. Detailed Chapter Summary and Core Concepts

A. Origin of Life and the Biosphere

• Primeval Life: Life on Earth originated millions of years ago in oceanic water bodies, commencing with primitive aquatic plants (flora) that gradually evolved into diverse marine and terrestrial fauna.
• The Biosphere: Earth is the only known planet in the solar system sustaining life. The narrow zone of interaction between the lithosphere, hydrosphere, and atmosphere where life thrives is called the biosphere.
• Early Humans: The earliest biological human ancestors who emerged on Earth’s surface are scientifically known as Homosapiens.

B. The Ecosystem and Trophic Interdependence

An ecosystem is the functional community formed by the complex interrelationship and interdependence between living organisms (plants, animals, microorganisms, humans) and their non-living physical environment (soil, water, air, sunlight):

• Producers (Food Factories): Green plants harness solar energy, atmospheric carbon dioxide, water, and soil minerals to synthesize organic food through photosynthesis. They are the primary food factories sustaining the entire biosphere.
• Consumers: Organisms that cannot produce their own food and depend on plants directly (herbivores) or indirectly (carnivores and omnivores). Humans are primary omnivores consuming both plant and animal products.
• Decomposers: Soil microorganisms (bacteria and fungi) that break down dead plant and animal tissues into simple inorganic chemical nutrients, returning them to the soil to nourish new plant growth.
• Food Chains and Food Webs: The unidirectional transfer of food energy from primary producers through a series of consumer organisms constitutes a food chain. Interlocking networks of multiple food chains in a natural habitat form a food web.

C. World Vegetation Belts (The Plant Kingdom)

Natural vegetation varies globally according to regional temperatures and precipitation patterns, classified into four major belts:

D. Animal Adaptations and Ecological Balance

• Ecosystem Adaptations: Animals adapt biologically to their habitats. Equatorial forests house tree-dwelling monkeys, snakes, and crocodiles; grasslands host swift herbivores (deer, zebras) and predators (lions, leopards); polar regions shelter polar bears, yaks, penguins, and arctic foxes equipped with thick insulating fur and heavy blubber fat layers.
• Ecological Imbalance & Threats: Rapid human population growth, reckless deforestation for urban settlements, industrial pollution, and illegal wildlife poaching have pushed apex species like tigers and Asiatic lions toward extinction and triggered catastrophic global climate warming.
• Conservation Measures: Restoring ecological stability requires nationwide afforestation, strict legal bans on wildlife trade, and establishing protected National Parks, Wildlife Sanctuaries, and Biosphere Reserves.

2. Key Terms and Definitions

3. Complete Textbook Exercise Solutions

Section A: Tick (✓) the Correct Option

1. Which one of the following is a threat to ecological balance?
(a) plantation
(b) wildlife protection
(c) population growth [✓]
(d) growing crops
Answer: (c) population growth

2. Taiga is:
(a) a Russian name for evergreen coniferous forests [✓]
(b) an animal living in the polar region
(c) a softwood tree
(d) a cold desert area
Answer: (a) a Russian name for evergreen coniferous forests

3. For the preservation of varied plant and animal life, the government has set up various:
(a) zoological parks
(b) industrial parks
(c) national parks [✓]
(d) adventure parks
Answer: (c) national parks

4. Mosses and lichens are:
(a) commonly found vegetation in the polar regions [✓]
(b) trees found in tropical deciduous forests
(c) insect-eating animals
(d) animals having thick fur on their body
Answer: (a) commonly found vegetation in the polar regions

5. The temperate grasslands of North America are called the:
(a) atacama
(b) veld
(c) prairies [✓]
(d) campos
Answer: (c) prairies

Section B: Fill in the Blanks

• 1. The first form of life on the earth appeared in the water bodies belonging to flora world.
• 2. The living zone of the planet earth is known as biosphere.
• 3. The human beings, who first appeared on the earth, were known as Homosapiens.
• 4. The Taiga vegetation is also known as Coniferous forests.
• 5. The plants prepare their own food and are known as food factories / producers of the biosphere.

Section C: Write True or False for the Following Statements

1. In the grasslands, the number of animals is less as compared to those in the equatorial forest.
Answer: True (Equatorial rainforests boast far greater biodiversity and animal populations).

2. Afforestation causes rise in the pollution level in the atmosphere.
Answer: False (Afforestation cleanses the air and reduces atmospheric pollution).

3. Tiger and lion are the endangered species in India.
Answer: True (Both apex carnivores face grave extinction threats due to poaching and habitat loss).

4. Pampas are the temperate grasslands in Australia.
Answer: False (Pampas are in South America; temperate grasslands of Australia are called Downs).

5. Insect-eating animals are most commonly found in the dense forests of the equatorial region.
Answer: True (Specialized insect-eaters like armadillos thrive in equatorial forest floors).

Section D: Answer the Following Questions in Brief

Question 1. Name the major types of vegetation of the world.
Answer: The four major types of world vegetation are:
1. Tropical Hardwood Forests (Evergreen and Deciduous)
2. Grasslands (Tropical Savannas and Temperate Grasslands)
3. Deserts (Hot Tropical Deserts and Cold Polar Tundra)
4. Temperate Softwood / Coniferous Forests (Taiga).

Question 2. Name some common plants found in cold and hot desert regions of the world.
Answer:
• Hot Desert Regions: Cacti, thorny scrub, acacia, date palms, and coarse drought-resistant bushes.
• Cold Desert Regions (Tundra): Mosses, lichens, and stunted dwarf sedges.

Question 3. What are the major components of Ecosystem?
Answer: An ecosystem comprises two fundamental components:
1. Biotic Components (Living): Producers (green plants), Consumers (herbivores, carnivores, omnivores), and Decomposers (bacteria and fungi).
2. Abiotic Components (Non-living): Sunlight, air, atmospheric gases, water, mineral soil, and temperature.

Question 4. Give some examples of trees having needle-shaped leaves.
Answer: Evergreen softwood trees of the Coniferous (Taiga) forest belt possess needle-shaped leaves to shed snow and prevent water loss. Examples include Pine, Fir, Spruce, and Larch.

Question 5. Why do animals in the polar region have thick fur on their bodies?
Answer: Animals native to polar regions (such as polar bears, arctic foxes, and yaks) possess thick, insulating fur coats and dense subcutaneous layers of fat (blubber) to trap body heat and survive sub-zero freezing temperatures and biting blizzard winds.

Section E: Answer the Following Questions in Detail

Question 1. Why are equatorial forests known as evergreen forests? Give a few examples of trees found there.
Answer:

• Reason: Equatorial forests are situated in the equatorial trough (10°N to 10°S) where uniformly high temperatures and heavy convectional rainfall prevail throughout the year. Because there is no distinct dry season or drought period, different tree species shed, grow new foliage, and flower at different times of the year. Consequently, the forest canopy never appears bare and remains verdant and green all year round.
• Characteristic Tree Species: Prominent commercial hardwood trees include Ebony, Mahogany, Rosewood, Rubber, and Cinchona.

Question 2. What role do plants play in ecological balance?
Answer: Plants are the indispensable anchors of global ecological balance through three vital functions:

• 1. Atmospheric Gas Regulation: Through photosynthesis, green plants absorb vast amounts of carbon dioxide (a potent greenhouse gas) and release fresh oxygen, maintaining the vital oxygen-carbon dioxide balance necessary for animal respiration.
• 2. Primary Producers in the Food Web: Plants function as the foundational food factories of the biosphere, converting abiotic solar energy into digestible organic nourishment for herbivores, which in turn feed carnivores.
• 3. Soil and Hydrological Conservation: Dense root networks bind topsoil, preventing water and wind erosion, enhancing groundwater recharge, and transpiring moisture to facilitate cloud formation and rainfall.

Question 3. Distinguish between tropical and temperate grasslands.
Answer:

Question 4. Differentiate between hot and cold deserts.
Answer:

Question 5. What are the various problems related to the ecological imbalance? What steps should we take to solve them?
Answer:

• Problems of Ecological Imbalance:
  1. Rampant Deforestation & Habitat Destruction: Large-scale destruction of forests for urbanization and agriculture leads to severe soil erosion and erratic monsoons.
  2. Wildlife Extinction Crisis: Uncontrolled poaching and habitat fragmentation have pushed apex species like tigers, rhinos, and lions to the verge of extinction.
  3. Global Climate Warming: Excessive greenhouse gas buildup from burning forests and fossil fuels accelerates polar ice melting and causes extreme weather catastrophes.
• Constructive Solutions to Restore Balance:
  1. Large-scale Afforestation: Undertake nationwide tree plantation campaigns to restore green cover and capture surplus carbon.
  2. Enforce Wildlife Protection Laws: Implement severe punitive penalties against illegal hunting, poaching, and animal contraband trade.
  3. Expand Protected Habitats: Broaden the network of strictly managed National Parks, Wildlife Sanctuaries, and Biosphere Reserves.
  4. Promote Public Awareness: Integrate ecological ethics into school curriculums and celebrate national Wildlife Conservation Weeks to engage local communities.

4. Value Based Questions (VBQ) and HOTS

Value Based Question (VBQ)

Context: ‘The Asiatic lion, once found across a vast area, is today crammed into a small scrubby forest of Gir in the south of Gujarat. Today, violence towards nature has caused retreat of forests, endangered species and also various sufferings to the mankind. Clearly the ideals of reverence for life have been renounced in favour of a materialistic way of life that justifies the destruction of nature and man both.’

1. What values should be adopted in life for preservation of plant and animal diversity?
Answer: We must cultivate:
• Reverence for All Life: Acknowledging that every living organism possesses an inherent right to exist.
• Compassion and Empathy: Treating wild fauna with kindness rather than exploiting them for commercial greed.
• Environmental Stewardship: Practicing sustainable living, planting trees, and rejecting consumer goods made from animal parts.
• Interdependence Awareness: Recognizing that human survival and well-being are intrinsically tied to biological diversity.

2. How far do you agree/disagree with those who justify destruction of nature and man both?
Answer: I completely and unequivocally disagree with those who rationalize the exploitation and destruction of nature for short-sighted material gains. Degrading ecosystems destroys clean water cycles, alters fertile climates, triggers pandemics, and eventually causes the collapse of human civilization itself. True economic progress must be ecologically sustainable.

HOTS (Higher Order Thinking Skills)

Q1. Why are coniferous forests (Taiga) suitable for commercial lumbering compared to tropical hardwood forests?
Answer: Coniferous forests consist of pure, homogeneous stands of a few softwood tree species (such as pine, fir, and spruce) that grow in straight, uniform trunks with minimal undergrowth, making mechanized cutting and transportation efficient. In contrast, tropical hardwood forests are dense, tangled, and feature hundreds of heterogeneous tree species mixed together in swampy, inaccessible terrain, making commercial selective lumbering economically unviable.

Q2. If all green plants disappeared from the biosphere, what would be the immediate and long-term consequences on the food chain?
Answer: Because green plants are the sole autotrophic primary producers of the biosphere, their total disappearance would immediately cut off the food supply for primary consumer herbivores (deer, cattle, rabbits), causing them to starve to death within weeks. Consequently, secondary and tertiary carnivores (lions, tigers, eagles) would lose their prey base and face extinction, while atmospheric oxygen would deplete rapidly, resulting in the total collapse of all animal and human life.

5. Something To Do / Map Skill & Activities

A. World Outline Map Marking

• (a) Tropical Evergreen Forests: Amazon River Basin (South America) and Congo/Zaire Basin (Africa).
• (b) Tropical Deciduous Forests: Central and Peninsular India, Myanmar, and Indo-China.
• (c) Tropical Grasslands: African Savannas and Brazilian Campos.
• (d) Temperate Grasslands: Prairies (Central North America) and Steppes (Central Eurasia).
• (e) Hot Deserts: Sahara Desert (North Africa) and Thar Desert (North-Western India).
• (f) Cold Deserts: Tundra belt along Northern Siberia (Russia) and Northern Canada.
• (g) Coniferous Forests: Expansive Taiga belt spanning Northern Canada, Scandinavia, and Northern Russia.

B. Wildlife Scrapbook & School Activity

• Indian Conservation Sanctuaries Portfolio: Collect pictures and notes on Gir National Park (Asiatic Lions), Jim Corbett National Park (Bengal Tigers), and Kaziranga National Park (One-horned Rhinoceros).
• Critically Endangered Species Fact-sheet: Research and compile conservation reports on the Forest Owlet, Ganges Shark, and Leatherback Sea Turtle.
• Wildlife Week Celebration (October 2 to 8): Conduct schoolyard tree-planting initiatives and establish bird water-baths and nest boxes to foster urban biodiversity.

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