Chapter 16 — Environmental Issues — is the final chapter covering pollution, waste management, deforestation, ozone depletion, and global warming. Carries 4-6 marks and is highly relevant to current affairs.
Key Concepts
Air Pollution
| Pollutant | Source | Effect |
|---|---|---|
| CO | Vehicle exhaust, incomplete combustion | Binds to Hb → reduces O₂ transport |
| SO₂, NOₓ | Fossil fuels, industries | Acid rain (pH < 5.6), respiratory problems |
| Particulate matter (SPM) | Construction, vehicles | Respiratory issues, reduced visibility |
| CFCs | Refrigerants, aerosols | Ozone depletion |
Catalytic Converter
Fitted in vehicles; contains Pt, Pd, Rh catalysts. Converts CO → CO₂, NOₓ → N₂, unburnt HC → CO₂ + H₂O. Unleaded petrol required (lead inactivates catalyst).
Water Pollution
- Eutrophication: Excess nutrients (N, P from fertilisers/sewage) → algal bloom → O₂ depletion → fish death
- BOD: High BOD = polluted water. Sewage treatment reduces BOD.
- Biomagnification: Concentration of toxic substances (DDT, mercury) increases at each trophic level. DDT in lake water: 0.003 ppm → in fish-eating birds: 25 ppm
Solid Waste Management
- Sanitary landfill: Waste compacted and covered with soil
- Incineration: Burning waste at high temperature (for hospital waste)
- Composting: Organic waste → compost (biodegradable waste)
- E-waste: Electronic waste; contains toxic metals; needs careful recycling
- Integrated Waste Management: Reduce → Reuse → Recycle
Ozone Depletion
Good ozone: In stratosphere (15-30 km) — protects from UV radiation
Bad ozone: In troposphere — pollutant
CFCs → Cl radicals → destroy O₃
Cl + O₃ → ClO + O₂ ; ClO + O → Cl + O₂ (Cl recycled — 1 Cl atom destroys ~100,000 O₃ molecules)
Ozone hole: Discovered over Antarctica
Montreal Protocol (1987): International agreement to phase out CFCs
Bad ozone: In troposphere — pollutant
CFCs → Cl radicals → destroy O₃
Cl + O₃ → ClO + O₂ ; ClO + O → Cl + O₂ (Cl recycled — 1 Cl atom destroys ~100,000 O₃ molecules)
Ozone hole: Discovered over Antarctica
Montreal Protocol (1987): International agreement to phase out CFCs
Global Warming & Greenhouse Effect
- Greenhouse gases: CO₂, CH₄, N₂O, CFCs, water vapour
- Trap heat in atmosphere → global temperature rises
- Effects: sea level rise, melting glaciers, extreme weather, coral bleaching
- Kyoto Protocol (1997): Binding targets for reducing GHG emissions
Deforestation
- Causes: agriculture, urbanisation, logging, mining
- Effects: soil erosion, loss of biodiversity, CO₂ increase, desertification
- Chipko Movement (1974): Gaura Devi and villagers hugged trees to prevent logging in Garhwal Himalayas
- Joint Forest Management (JFM): Government + local communities manage forests together
Case Studies
| Issue | Solution |
|---|---|
| Vehicular pollution in Delhi | CNG conversion of public transport, Bharat Stage emission norms |
| Noise pollution | Green belt of trees, silencers, noise barriers |
| Radioactive waste | Deep geological burial, nuclear waste treatment |
| Agrochemical pollution | Organic farming, IPM (Integrated Pest Management) |
Quick Revision Points
- Air pollution: CO, SO₂, NOₓ, SPM, CFCs; Catalytic converter: Pt-Pd-Rh
- Water pollution: eutrophication (algal bloom), biomagnification (DDT)
- Ozone depletion: CFCs → Cl radicals; Montreal Protocol (1987)
- Global warming: CO₂, CH₄; Kyoto Protocol (1997)
- Deforestation: Chipko Movement (1974), JFM
- Solid waste: reduce-reuse-recycle; sanitary landfill, incineration, composting
- Biomagnification: DDT increases at each trophic level
- BOD: high = polluted; reduced by sewage treatment
Chapter Navigation
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Related Chapters in Class 12 Biology
- Biodiversity and Conservation Class 12 Notes
- Organisms and Populations Class 12 Notes
- Ecosystem Class 12 Notes
Practice What You Learned
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