class 12 notes

Class 12 Biology Notes Chapter 16 (Environmental issues) – Biology Book

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Philoid

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Biology
Detailed Notes with MCQs of Chapter 16, 'Environmental Issues'. This is a crucial chapter, not just for your board exams but also frequently features in various government competitive examinations. Pay close attention to the details, causes, effects, and control measures discussed.

Chapter 16: Environmental Issues - Detailed Notes for Competitive Exams

1. Pollution:
Any undesirable change in the physical, chemical, or biological characteristics of air, land, water, or soil. Agents causing pollution are called pollutants.

A. Air Pollution:

  • Sources: Thermal power plants (fly ash, SO₂, NOx), Industries, Vehicular emissions (CO, CO₂, NOx, lead, particulate matter), Burning of fossil fuels, Agricultural activities (stubble burning), Smelters.
  • Major Air Pollutants & Effects:
    • Particulate Matter (PM): Fine particles (PM 2.5 are most harmful) can penetrate deep into lungs causing respiratory problems, inflammation, premature death. Reduces visibility.
    • Sulphur Dioxide (SO₂): Respiratory issues, acid rain (damages vegetation, buildings - Taj Mahal affected).
    • Nitrogen Oxides (NOx): Respiratory problems, acid rain, smog formation.
    • Carbon Monoxide (CO): Reduces oxygen-carrying capacity of blood by binding strongly to haemoglobin. Can be fatal.
    • Ozone (O₃) in Troposphere ('Bad' Ozone): Formed by reaction of NOx and Volatile Organic Compounds (VOCs) in sunlight. Causes respiratory problems, damages vegetation.
    • Lead (Pb): Affects nervous system, especially in children. (Phased out from petrol).
  • Control Measures:
    • Electrostatic Precipitators (ESPs): Remove >99% particulate matter from industrial/thermal plant exhausts. High voltage creates a corona that charges dust particles, which are then collected on grounded plates.
    • Scrubbers: Remove gases like SO₂. Exhaust passed through a spray of water or lime. Also removes particulate matter.
    • Catalytic Converters: Fitted in automobiles. Contain expensive metals (Platinum-Palladium and Rhodium) as catalysts. Convert unburnt hydrocarbons to CO₂ and H₂O; CO to CO₂; NOx to N₂. Requires unleaded petrol (lead inactivates the catalyst).
    • Fuel Efficiency & Alternatives: Promoting public transport, phasing out old vehicles, using low-sulphur fuel, Compressed Natural Gas (CNG) (burns efficiently, cheaper). Case Study: Delhi's switch to CNG for public transport significantly reduced CO and CO₂ levels.
    • Emission Standards: Bharat Stage Emission Standards (e.g., BS-VI) regulate vehicular pollutant output.
    • Noise Pollution: Included as air pollution under the Air (Prevention and Control of Pollution) Act, 1981 (amended in 1987). Noise > 150 dB can damage eardrums. Chronic exposure to lower noise levels can cause sleeplessness, stress, hypertension. Control: Sound-absorbent materials, enforcing noise level limits, horn-free zones, green muffler (planting trees).

B. Water Pollution:

  • Sources: Domestic sewage, Industrial effluents, Agricultural runoff (fertilizers, pesticides), Thermal power plants (hot water), Oil spills, Solid waste dumping.
  • Effects:
    • Water-borne Diseases: Typhoid, cholera, dysentery, jaundice (caused by pathogens in sewage).
    • Oxygen Depletion: Biodegradable organic matter increases microbial activity, consuming Dissolved Oxygen (DO). Measured by Biochemical Oxygen Demand (BOD) - amount of O₂ needed by microbes to decompose organic matter. High BOD indicates high pollution and low DO. A sharp decline in DO downstream from a sewage discharge point causes fish mortality.
    • Eutrophication: Nutrient enrichment of water bodies (Nitrates, Phosphates from fertilizers, sewage). Leads to excessive growth of planktonic algae (Algal Blooms), imparting colour, deteriorating water quality, causing fish mortality due to oxygen depletion upon decomposition. Can be natural (slow) or Cultural/Accelerated (human-induced, fast).
    • Biomagnification: Increase in concentration of persistent toxic substances (e.g., DDT, Mercury) at successive trophic levels. DDT accumulation disrupts calcium metabolism in birds (thin eggshells). Mercury causes Minamata disease (Japan).
    • Thermal Pollution: Hot wastewater reduces DO (less soluble at high temp) and affects aquatic organisms sensitive to temperature changes.
  • Control Measures:
    • Sewage Treatment Plants (STPs):
      • Primary Treatment: Physical removal of particles (filtration, sedimentation).
      • Secondary Treatment (Biological): Microbial decomposition of organic matter (activated sludge method, trickling filters). Reduces BOD.
      • Tertiary Treatment: Removal of specific pollutants, disinfection (often not done).
    • Integrated Wastewater Treatment: Combining artificial and natural processes. Case Study: Arcata Marsh, California - collaboration with Humboldt State University biologists. Conventional treatment followed by passage through marshes with algae, fungi, bacteria, and plants that neutralize, absorb, and assimilate pollutants. Creates a sanctuary.
    • Controlling Runoff: Promoting organic farming, judicious use of fertilizers/pesticides.
    • Legislation: Water (Prevention and Control of Pollution) Act, 1974.

C. Soil Pollution:

  • Sources: Pesticides, herbicides, fertilizers, industrial wastes, mining activities, leakage from landfills, plastic waste.
  • Effects: Reduced soil fertility, kills soil microflora/fauna, biomagnification through food chain, groundwater contamination.
  • Control: Reducing chemical use (Organic Farming, Integrated Pest Management - IPM), proper disposal of industrial/municipal waste, bioremediation, planting trees.

2. Solid Wastes:

  • Types: Municipal solid waste (household, office, school waste), Industrial waste, Hospital waste (hazardous), Electronic waste (e-waste).
  • Management:
    • Source Reduction & Reuse: Minimizing waste generation.
    • Recycling: Processing waste materials to create new products (paper, plastic, metal, glass).
    • Composting: Decomposition of organic waste into manure.
    • Incineration: Burning waste at high temperatures (reduces volume but can cause air pollution if not controlled). Often used for hospital waste.
    • Landfills: Waste dumped in depressions or trenches. Sanitary Landfills involve compaction and daily covering with dirt to prevent pests and odour, with leachate collection systems. Open dumps are unsanitary.
  • Case Studies:
    • Plastic Waste Remedy: Ahmed Khan, a plastic sack manufacturer in Bengaluru, developed Polyblend - fine powder of recycled plastic. Mixed with bitumen, it enhances road water-repellent properties and increases road life.
    • E-Waste: Irreparable computers/electronics. Rich in metals (copper, iron, silicon, nickel, gold) but also contain toxic substances. Developed countries often export e-waste to developing countries (China, India, Pakistan) where recycling involves manual labour exposing workers to toxins. Need for safe recycling facilities.

3. Agro-chemicals and their Effects:

  • Problem: Excessive use of inorganic fertilizers causes eutrophication; pesticides/herbicides kill non-target organisms, lead to biomagnification (DDT), and contaminate soil/water.
  • Solution: Integrated Organic Farming: Cyclical, zero-waste procedure. Waste from one process used as nutrient for another. Includes composting, vermiculture, crop rotation, biological pest control. Maximizes resource utilization, increases efficiency, economically viable. Case Study: Ramesh Chandra Dagar, Sonipat, Haryana - integrated bee-keeping, dairy, water harvesting, composting, agriculture.

4. Radioactive Wastes:

  • Sources: Nuclear power generation, medical/research use of radioisotopes.
  • Problem: Highly hazardous, cause mutations, cancer. Accidental leakages (e.g., Three Mile Island, Chernobyl) are catastrophic.
  • Disposal: Requires careful handling. Pre-treatment, storage in shielded containers, burial about 500m deep within rocks. Public opposition often hinders disposal site selection.

5. Greenhouse Effect and Global Warming:

  • Greenhouse Effect: Natural phenomenon where atmospheric gases (Greenhouse Gases - GHGs) trap heat, keeping Earth warm. Without it, average temp would be -18°C instead of 15°C.
  • Enhanced Greenhouse Effect (Global Warming): Increase in GHG levels due to human activities traps more heat, leading to rise in global mean temperature.
  • GHGs & Relative Contribution: CO₂ (60%), Methane (CH₄) (20%), Chlorofluorocarbons (CFCs) (14%), Nitrous Oxide (N₂O) (6%).
  • Sources of Increase: Burning fossil fuels (CO₂), Deforestation (reduces CO₂ uptake), Paddy fields, Cattle, Biomass burning (CH₄), Refrigerants, Aerosols (CFCs), Fertilizers, Biomass burning (N₂O).
  • Consequences: Melting of polar ice caps/glaciers, sea-level rise (submerging coastal areas), changes in precipitation patterns (more droughts/floods), increased frequency of extreme weather events (El Nino effect intensification), impact on agriculture and ecosystems.
  • Control: Reduce fossil fuel use (increase energy efficiency, promote renewables), afforestation, reduce N₂O/CH₄ emissions from agriculture, international initiatives like the Kyoto Protocol (commitments to reduce GHG emissions).

6. Ozone Depletion in the Stratosphere:

  • 'Good' Ozone: Found in the stratosphere (upper atmosphere). Absorbs harmful UV-B radiation from the sun. Thickness measured in Dobson Units (DU).
  • Ozone Depleting Substances (ODS): Primarily Chlorofluorocarbons (CFCs) used as refrigerants, propellants, solvents. Also Halons.
  • Mechanism: UV radiation breaks down CFCs in the stratosphere, releasing Chlorine (Cl) atoms. Cl acts as a catalyst, degrading ozone (O₃) into O₂. One Cl atom can destroy thousands of O₃ molecules.
  • Ozone Hole: Thinning of the ozone layer, particularly marked over Antarctica during spring (Aug-Oct).
  • Effects of Increased UV-B: DNA damage (mutations), skin aging, skin cancers (melanoma), snow-blindness, cataracts, damage to cornea, suppressed immune function, reduced productivity of phytoplankton and terrestrial plants.
  • Control: Montreal Protocol (1987) - International treaty to phase out production and consumption of ODS. Effective in curbing ozone depletion.

7. Degradation by Improper Resource Utilisation:

  • Soil Erosion & Desertification: Removal of fertile topsoil by wind/water due to deforestation, over-grazing, unsustainable agriculture (e.g., slash-and-burn/Jhum cultivation in NE India), improper irrigation. Leads to loss of productivity and eventual desertification.
  • Waterlogging & Soil Salinity: Poor drainage in irrigated lands leads to waterlogging. Water evaporates, leaving salts behind (salinisation), making soil infertile. Affects large areas in India.

8. Deforestation:

  • Definition: Conversion of forested areas to non-forested ones.
  • Causes: Conversion to agricultural land (historically major cause), timber harvesting, firewood collection, development projects (dams, roads), mining, urbanization, slash-and-burn agriculture (Jhum).
  • Consequences: Loss of biodiversity, habitat destruction, soil erosion, desertification, disruption of hydrological cycle (altered rainfall patterns), increased atmospheric CO₂.
  • Conservation Efforts:
    • Reforestation: Restoring forests. Can occur naturally if area is left undisturbed.
    • Afforestation: Planting forests in new areas.
    • Case Study: Chipko Movement (1974): Started in Garhwal Himalayas (Uttarakhand). Local women hugged trees to protect them from contractors' axes. Led by figures like Sunderlal Bahuguna, Gaura Devi. Highlighted community participation in forest conservation.
    • Joint Forest Management (JFM): Government of India concept (1980s). Involves local communities in managing and protecting forests. Communities get benefits like minor forest products in return.
    • National Forest Policy (1988): Recommends 33% forest cover for plains and 67% for hills. Emphasizes sustainable forest management and community participation.

9. Key Environmental Legislation in India:

  • Environment (Protection) Act, 1986: Umbrella act enacted after Bhopal Gas Tragedy. Provides framework for coordinating activities of various agencies and addressing environmental issues comprehensively.
  • Air (Prevention and Control of Pollution) Act, 1981 (amended 1987 to include noise).
  • Water (Prevention and Control of Pollution) Act, 1974.
  • Wildlife (Protection) Act, 1972.
  • Forest (Conservation) Act, 1980.

Multiple Choice Questions (MCQs):

  1. Which of the following metals is used as a catalyst in catalytic converters for reducing automobile emissions?
    a) Lead
    b) Mercury
    c) Rhodium
    d) Iron

  2. Biochemical Oxygen Demand (BOD) is a measure of:
    a) Industrial pollution only
    b) Dissolved oxygen needed by microbes to decompose organic matter
    c) The amount of oxygen present in highly polluted water
    d) Oxygen released by algae during photosynthesis

  3. The phenomenon where the concentration of persistent toxins like DDT increases at successive trophic levels is called:
    a) Eutrophication
    b) Biomagnification
    c) Biodegradation
    d) Bioremediation

  4. Which international treaty was signed to control the emission of ozone-depleting substances?
    a) Kyoto Protocol
    b) Earth Summit
    c) Montreal Protocol
    d) Ramsar Convention

  5. Polyblend, a fine powder of recycled modified plastic, developed by Ahmed Khan, has been proven to be a good material for:
    a) Making plastic furniture
    b) Use as fertilizer
    c) Construction of roads
    d) Making insulation material

  6. Which of the following is NOT a major greenhouse gas?
    a) Carbon dioxide (CO₂)
    b) Methane (CH₄)
    c) Oxygen (O₂)
    d) Nitrous oxide (N₂O)

  7. The thickness of the ozone layer in a column of air from the ground to the top of the atmosphere is measured in terms of:
    a) Decibels (dB)
    b) Dobson Units (DU)
    c) Parts Per Million (ppm)
    d) Pascal (Pa)

  8. The 'Chipko Movement', concerned with forest conservation, originated in:
    a) Kerala
    b) Garhwal Himalayas (Uttarakhand)
    c) Karnataka
    d) Madhya Pradesh

  9. Electrostatic precipitators are widely used to remove which type of pollutant from industrial exhaust?
    a) Sulphur dioxide
    b) Carbon monoxide
    c) Particulate matter
    d) Oxides of nitrogen

  10. Cultural or accelerated eutrophication is primarily caused by:
    a) Accumulation of heavy metals
    b) Hot water discharge from industries
    c) Nutrient enrichment from sewage and agricultural runoff
    d) Increased sedimentation

Answer Key for MCQs:

  1. c) Rhodium (also Platinum-Palladium)
  2. b) Dissolved oxygen needed by microbes to decompose organic matter
  3. b) Biomagnification
  4. c) Montreal Protocol
  5. c) Construction of roads
  6. c) Oxygen (O₂)
  7. b) Dobson Units (DU)
  8. b) Garhwal Himalayas (Uttarakhand)
  9. c) Particulate matter
  10. c) Nutrient enrichment from sewage and agricultural runoff

Revise these notes thoroughly. Understanding the concepts, remembering key facts, case studies, and legislation will be very helpful for your exams. Good luck!

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