Man and Environment — Class 9 Social Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 9 Social Science, Geography — Chapter 6. How humans impact and depend on the environment.

1. About this lesson

This chapter explores the relationship between humans and the environment — how humans modify nature, the resulting environmental problems, and the need for sustainable development.

2. Human-Environment Interaction

• Humans depend on the environment for resources (air, water, food, raw materials).
• Humans modify the environment through agriculture, industry, urbanization, mining, transport.
• Environmental degradation: Deterioration of the environment through depletion of resources and destruction of ecosystems.

3. Types of Pollution

Key terms

• Acid rain: Sulphur dioxide and nitrogen oxides from industries → dissolve in rainwater → acidic rain. Damages buildings (e.g., Taj Mahal), soil, forests, water bodies.
• Eutrophication: Excess nutrients (from fertilizers) in water bodies → excessive algae growth → depletion of oxygen → death of aquatic life.
• Smog: Smoke + fog; common in industrial cities.

4. Deforestation

• Clearing of forests for agriculture, urbanization, industry, mining, timber.
• Effects: soil erosion, loss of biodiversity, climate change, desertification, disruption of water cycle.

5. Global Warming and Climate Change

• Greenhouse Effect: Greenhouse gases (CO₂, methane, CFCs, nitrous oxide) trap heat in the atmosphere → Earth's temperature rises.
• Global Warming: Gradual increase in Earth's average surface temperature due to increased greenhouse gases.
• Climate Change: Long-term changes in weather patterns — more extreme events (floods, droughts, cyclones), rising sea levels, melting glaciers.

Major sources of greenhouse gases

• Burning fossil fuels (CO₂).
• Deforestation (reduces CO₂ absorption).
• Agriculture (methane from livestock, rice paddies).
• Industrial processes (CFCs, nitrous oxide).

6. Sustainable Development

• Sustainable Development: Development that meets the needs of the present without compromising the ability of future generations to meet their own needs (Brundtland Commission, 1987).
• 3 pillars: Economic, Social, Environmental.

Measures for Environmental Conservation

• Afforestation and reforestation.
• Renewable energy (solar, wind, hydro, biogas).
• Reduce, Reuse, Recycle (3Rs).
• Pollution control laws and standards.
• Environmental education and awareness.
• Wildlife conservation (Project Tiger, Project Elephant).

7. Worked examples

Example 1. What is acid rain? Rain containing sulphuric and nitric acids from industrial emissions (SO₂, NOₓ).

Example 2. Define sustainable development. Development meeting present needs without compromising future generations' ability to meet theirs (Brundtland, 1987).

Example 3. Name two greenhouse gases. Carbon dioxide (CO₂) and methane (CH₄).

Example 4. When is World Population Day? July 11th every year.

8. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

1. The surroundings where organisms live is called — (a) Environment / (b) Ecosystem / (c) Biotic factors / (d) Abiotic factors. Ans: (a) Environment.

2. 'World Population Day' is observed on — (a) August 11th / (b) September 11th / (c) July 11th / (d) January 11th. Ans: (c) July 11th.

3. The statistical study of human population is — (a) Demography / (b) Morphology / (c) Etymology / (d) Seismography. Ans: (a) Demography.

4. The extraction of valuable minerals and other geological minerals from the mines is — (a) Fishing / (b) Lumbering / (c) Mining / (d) Agriculture. Ans: (c) Mining.

5. The Secondary sector of the economy produces — (a) Semi-finished goods / (b) Finished goods / (c) Economic goods / (d) Raw materials. Ans: (b) Finished goods.

6. Gradual increase of the Earth's temperature by greenhouse gases is called — (a) Acid rain / (b) Thermal pollution / (c) Global warming / (d) Deforestation. Ans: (c) Global warming.

II. Match the following

III. Assertion and Reason

7. A: Ozone layer in the stratosphere is a protective shield. R: It prevents UV radiation from reaching Earth's surface. — (a) A and R are correct and A explains R.

8. A: In tertiary activities, instead of producing goods by themselves, they are in the process of production. R: People in tertiary activities are purely eco-friendly. — (c) A is correct and R is incorrect.

IV. Answer in brief

9. What is 'density of population'? — Number of people living per square kilometre. Sparse = large area, fewer people. Dense = smaller area, many people.

10. What is 'Black Death'? — Killed 30–60% of Europe's population in the 14th century. Attributed to the outbreak of plague.

11. High and low density areas. — High density (above 50 people/sq km): East Asia, South Asia, NW Europe, Eastern North America. Low density (less than 10): Central Africa, Western Australia, Northern Russia, Canada.

12. Restoration of Palk Bay. — Saplings of native species grown. Live coral colonies from Gulf of Mannar transplanted to Palk Bay. Mangroves mapped. Communities given livelihood training beyond fishing.

13. Define:

    • Population growth: Increase in number of people in a particular area during a period.
    • Infant Mortality Rate (IMR): Number of deaths under one year of age per 1000 live births in a year.
    • Census: Official enumeration of population carried out periodically — records age, sex, literacy, occupation.
    • Sustainable Development: Development meeting present needs without compromising future generations' ability to meet their own needs (Brundtland Commission).

V. Give reasons

14. Reforestation is encouraged throughout the world. — Deforestation causes floods, droughts, soil fertility loss, air pollution, species extinction, global warming, desertification, melting ice caps, sea-level rise. Reforestation conserves the Earth.

15. Acid rain destroys the ecosystem. — Makes water acidic → aluminium absorbed from soil into lakes/streams. Limits plant nutrients, exposes them to toxic substances.

16. Quaternary sector = knowledge economy. — Deals with Research & Development and knowledge. Services: consultation, education, banking.

17. Population growth must be controlled. — For sustainable development. Education about problems: pollution, resource scarcity, conflict, low living standards, ecological imbalance.

18. Sustainable development protects the planet. — Excessive resource use depletes availability for future generations. Conservation + awareness → sustainability. Our actions have lasting environmental effects.

VI. Distinguish between

19. Primary vs Secondary activities. — Primary: directly extract from nature (agriculture, fishing, mining, lumbering). Secondary: process raw materials into finished goods (manufacturing, construction).

20. Push factors vs Pull factors of migration. — Push: natural disasters, unemployment, conflict (drive people away). Pull: better living conditions, jobs, education (attract people).

9. Common mistakes

• Mistake: Global warming and climate change are exactly the same. Fix: Global warming = rise in temperature. Climate change = broader long-term changes in weather patterns.
• Mistake: Only industries cause pollution. Fix: Agriculture, vehicles, households, construction also contribute.
• Mistake: Deforestation only means cutting trees for timber. Fix: Deforestation also occurs for agriculture, urbanization, mining, and infrastructure.

9. Quick revision

• Geography Ch 6 · Man and Environment.
• Human activities → environmental degradation.
• Pollution: Air (vehicles, industries → acid rain, global warming), Water (sewage, chemicals → eutrophication), Soil (fertilizers, plastic), Noise (traffic).
• Deforestation → soil erosion, biodiversity loss, climate change.
• Global warming: Greenhouse gases (CO₂, CH₄, CFCs) trapping heat. Climate change → extreme weather, sea-level rise.
• Sustainable Development: meet present needs without harming future (Brundtland 1987). 3Rs, renewable energy, afforestation.