Class 12 Notes

Class 12 Biology Notes Chapter 16 (Environmental Issues) – Examplar Problems Book

Philoid

Philoid

— 6 min read

Examplar Problems
Detailed Notes with MCQs of a very crucial chapter for your exams and for understanding the world around us – 'Environmental Issues'. This chapter deals with the impact of human activities on our environment and the measures needed to mitigate the damage. Pay close attention, as questions from this section frequently appear in competitive exams.

Chapter 16: Environmental Issues - Detailed Notes

1. Introduction

  • Environmental issues arise primarily due to increasing human population, urbanization, industrialization, and unsustainable resource utilization.
  • Pollution is any undesirable change in the physical, chemical, or biological characteristics of air, land, water, or soil. Agents causing pollution are called pollutants.
  • The Government of India passed the Environment (Protection) Act, 1986 to protect and improve the quality of our environment.

2. Air Pollution and Its Control

  • Causes: Smoke from industries, thermal power plants, smelters, vehicle exhaust, burning of fossil fuels, particulate matter (PM), gaseous pollutants (SO2, NOx, CO, H2S).
  • Effects:
    • On Humans: Respiratory problems (asthma, bronchitis), irritation of eyes, nose, throat. Carbon monoxide (CO) reduces oxygen-carrying capacity of blood.
    • On Plants: Reduced growth and yield, premature death, necrosis, chlorosis. SO2 causes significant damage.
    • Acid Rain: Oxides of sulfur (SO2) and nitrogen (NOx) react with water vapour to form sulfuric acid (H2SO4) and nitric acid (HNO3), damaging vegetation, soil fertility, aquatic life, and monuments (e.g., Taj Mahal).
  • Control Measures:
    • Electrostatic Precipitators (ESPs): Remove over 99% of particulate matter from industrial/thermal plant exhaust. High voltage creates a corona that releases electrons, charging dust particles, which are then collected on grounded plates.
    • Scrubbers: Remove gases like SO2. Exhaust passes through a spray of water or lime.
    • Catalytic Converters: Fitted in automobiles. Contain expensive metals (platinum-palladium, rhodium) as catalysts. Convert unburnt hydrocarbons to CO2 and H2O, and CO & NO into CO2 & N2 gas. Requires unleaded petrol.
    • Vehicular Pollution Control (Case Study - Delhi): Phasing out old vehicles, use of unleaded petrol, low-sulfur petrol/diesel, catalytic converters, application of stringent emission norms (Bharat Stage norms - equivalent to Euro norms), switching public transport (buses) to Compressed Natural Gas (CNG). CNG burns cleaner and is cheaper.
    • Noise Pollution: Undesirable high level of sound. Sources: Industries, vehicles, loudspeakers, crackers. Effects: Sleeplessness, increased heart rate, altered breathing, stress, permanent hearing damage. Control: Use of sound-absorbent materials, enforcing noise level limits, horn-free zones around hospitals/schools.

3. Water Pollution and Its Control

  • Sources:
    • Domestic Sewage: Contains biodegradable organic matter, pathogens (bacteria, viruses, protozoa, helminths causing diseases like typhoid, cholera, jaundice, dysentery). 0.1% impurities make domestic sewage unfit for human use.
    • Industrial Effluents: Contain toxic heavy metals (mercury, cadmium, copper, lead), persistent organic pollutants.
    • Agricultural Runoff: Fertilizers (nitrates, phosphates) and pesticides.
    • Thermal Pollution: Heated wastewater from power plants reduces dissolved oxygen (DO).
  • Key Concepts:
    • Biochemical Oxygen Demand (BOD): Amount of dissolved oxygen needed by aerobic microorganisms to break down organic material present in a given water sample. High BOD indicates high pollution potential (high organic matter).
    • Dissolved Oxygen (DO): Crucial for aquatic life. Pollution decreases DO.
    • Algal Blooms: Excessive growth of planktonic algae, often due to nutrient enrichment (eutrophication). They deteriorate water quality, increase BOD, and can release toxins. Example: Water hyacinth (Eichhornia crassipes) - "Terror of Bengal".
    • Biomagnification: Increase in concentration of a toxicant (e.g., DDT, mercury) at successive trophic levels in a food chain. DDT disrupts calcium metabolism in birds, causing thin eggshells and premature breaking.
    • Eutrophication: Natural aging of a lake by nutrient enrichment. Cultural or Accelerated Eutrophication is caused by human activities (sewage, agricultural/industrial waste). Leads to algal blooms, oxygen depletion, and death of aquatic organisms.
  • Control Measures:
    • Sewage Treatment Plants (STPs): Primary (physical removal of particles), Secondary (biological treatment using microbes to reduce BOD), Tertiary (advanced chemical/physical processes to remove remaining impurities).
    • Integrated Wastewater Treatment: Combining artificial and natural processes. Example: Friends of the Arcata Marsh (FOAM), California - marshes used to filter and purify wastewater naturally.
    • Ecological Sanitation (EcoSan): Sustainable system for handling human excreta using dry composting toilets. Converts human waste into natural fertilizer, prevents water pollution. Practiced in Kerala and Sri Lanka.

4. Solid Wastes

  • Includes municipal solid waste (homes, offices, schools), industrial waste, hospital waste (hazardous), electronic waste (e-wastes).
  • Management:
    • Source Reduction & Recycling: The "3 Rs" - Reduce, Reuse, Recycle.
    • Composting: Breakdown of biodegradable waste.
    • Incineration: Burning, reduces volume but can cause air pollution if not done properly. Often used for hospital waste.
    • Sanitary Landfills: Waste dumped in depressions/trenches, compacted, and covered with dirt daily. Risk of leachate polluting groundwater.
    • Case Study (Plastic Waste Remedy - Ahmed Khan, Bengaluru): Developed Polyblend, a fine powder of recycled modified plastic. Mixed with bitumen, it enhances road life by increasing water-repellent properties.

5. Agro-chemicals and their Effects

  • Use of inorganic fertilizers and pesticides increased crop yields (Green Revolution) but caused pollution.
  • Effects: Eutrophication (fertilizers), biomagnification (pesticides like DDT), soil pollution, killing non-target organisms.
  • Solution: Organic Farming - relies on crop rotation, green manure, compost, biological pest control.
  • Case Study (Integrated Organic Farming - Ramesh Chandra Dagar, Sonipat): Zero-waste procedure involving bee-keeping, dairy management, water harvesting, composting, and agriculture in a chain process supporting each other.

6. Radioactive Wastes

  • Generated from nuclear power plants. Highly hazardous, cause mutations at high rates.
  • Disposal: Requires pre-treatment, storage in shielded containers, buried about 500m deep within rock formations. Highly controversial due to long-term risks.

7. Greenhouse Effect and Global Warming

  • Greenhouse Effect: Natural phenomenon where certain gases (Greenhouse Gases - GHGs) in the atmosphere trap heat, keeping the Earth warm.
  • Greenhouse Gases (GHGs): Carbon dioxide (CO2 - ~60%), Methane (CH4 - ~20%), Chlorofluorocarbons (CFCs - ~14%), Nitrous oxide (N2O - ~6%).
  • Global Warming: Increase in the average global temperature due to enhanced greenhouse effect caused by increased concentration of GHGs from human activities (burning fossil fuels, deforestation, agriculture).
  • Effects: Odd climatic changes (El Nino effect), melting of polar ice caps and glaciers, rising sea levels, submergence of coastal areas.
  • Control: Reduce fossil fuel use, improve energy efficiency, reduce deforestation, plant trees (afforestation), reduce N2O/CH4 emission, international initiatives (e.g., Kyoto Protocol).

8. Ozone Depletion in the Stratosphere

  • Ozone Layer ('Good Ozone'): Found in the stratosphere, absorbs harmful Ultraviolet-B (UV-B) radiation from the sun.
  • Ozone Depletion: Thinning of the ozone layer, particularly over Antarctica (ozone hole).
  • Cause: Chlorofluorocarbons (CFCs) used as refrigerants, in aerosols, etc. UV radiation causes CFCs to release active Chlorine (Cl) atoms in the stratosphere. Cl acts as a catalyst, degrading ozone (O3) into molecular oxygen (O2). One Cl atom can destroy thousands of ozone molecules.
  • Effects of Increased UV-B: Skin aging, skin cancers (melanoma), cataracts, damage to cornea, suppressed immune function, reduced phytoplankton productivity.
  • Control: Montreal Protocol (1987, effective 1989): International treaty to phase out the emission of Ozone Depleting Substances (ODS) like CFCs.

9. Degradation by Improper Resource Utilisation

  • Soil Erosion and Desertification: Removal of fertile topsoil by wind or water, often due to deforestation, over-cultivation, over-grazing, poor irrigation practices. Leads to desert formation.
  • Waterlogging and Soil Salinity: Excessive irrigation without proper drainage leads to waterlogging. Water evaporates, leaving salts behind, increasing soil salinity and damaging agriculture.

10. Deforestation

  • Conversion of forested areas to non-forested ones.
  • Causes: Conversion for agriculture (slash and burn / Jhum cultivation in North-Eastern states), logging, urbanization, infrastructure development.
  • Consequences: Enhanced CO2 concentration, habitat loss, biodiversity loss, soil erosion, desertification, disturbance of hydrologic cycle.
  • Conservation Efforts:
    • Reforestation: Restoring a forest that once existed.
    • Afforestation: Planting trees in areas where there were no forests before.
    • Chipko Movement (1974, Himalayas): Local women bravely protected trees from contractors by hugging them. Led by Gaura Devi, Sunderlal Bahuguna, Chandi Prasad Bhatt.
    • Joint Forest Management (JFM) (India, 1980s): Government works closely with local communities for protecting and managing forests. Communities get benefits like minor forest products.

Conclusion: Environmental protection requires individual, community, national, and international efforts. Sustainable development is key to ensuring resources are available for future generations.

Multiple Choice Questions (MCQs)

  1. Which of the following is responsible for biomagnification?
    (a) SO2
    (b) DDT
    (c) CO2
    (d) Fly ash

  2. The Montreal Protocol aims to:
    (a) Reduce greenhouse gas emissions
    (b) Control water pollution
    (c) Phase out ozone-depleting substances
    (d) Protect endangered species

  3. High Biological Oxygen Demand (BOD) in a water body indicates:
    (a) High level of dissolved oxygen
    (b) Low level of microbial pollution
    (c) High level of biodegradable organic matter
    (d) The water is pure and suitable for drinking

  4. Electrostatic precipitators are primarily used to remove which type of pollutant from industrial exhaust?
    (a) Gaseous pollutants like SO2
    (b) Particulate matter
    (c) Carbon monoxide
    (d) Ozone

  5. 'EcoSan' toilets, associated with ecological sanitation, primarily aim to:
    (a) Increase water consumption for hygiene
    (b) Treat sewage using chemicals before discharge
    (c) Use dry composting methods to convert human excreta into fertilizer
    (d) Filter water using reverse osmosis

  6. Which of the following contributes the most to the greenhouse effect?
    (a) Methane (CH4)
    (b) Nitrous Oxide (N2O)
    (c) Carbon Dioxide (CO2)
    (d) Chlorofluorocarbons (CFCs)

  7. The 'Chipko Movement' is primarily associated with:
    (a) Preventing water pollution in rivers
    (b) Protection of forests by preventing tree felling
    (c) Reducing air pollution in urban areas
    (d) Promoting organic farming

  8. Polyblend, developed by Ahmed Khan, is a mixture used for:
    (a) Making eco-friendly furniture
    (b) Constructing roads along with bitumen
    (c) Producing biodegradable plastics
    (d) Filtering industrial effluents

  9. Catalytic converters in vehicles require the use of:
    (a) Leaded petrol
    (b) Diesel with high sulfur content
    (c) Compressed Natural Gas (CNG)
    (d) Unleaded petrol

  10. Accelerated eutrophication of a lake is often caused by:
    (a) Introduction of exotic species
    (b) Accumulation of heavy metals
    (c) Input of nutrients like nitrates and phosphates from sewage and agriculture
    (d) Thermal pollution from power plants

Answer Key:

  1. (b) DDT
  2. (c) Phase out ozone-depleting substances
  3. (c) High level of biodegradable organic matter
  4. (b) Particulate matter
  5. (c) Use dry composting methods to convert human excreta into fertilizer
  6. (c) Carbon Dioxide (CO2)
  7. (b) Protection of forests by preventing tree felling
  8. (b) Constructing roads along with bitumen
  9. (d) Unleaded petrol
  10. (c) Input of nutrients like nitrates and phosphates from sewage and agriculture

Revise these notes thoroughly. Understanding the causes, effects, and control measures for each environmental issue, along with the specific case studies mentioned in NCERT, is vital for your exam preparation. Good luck!

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