Environmental Issues Class 12 Biology Chapter Notes

Key Definitions for Environmental Issues

Pollution

Any undesirable change in physical, chemical, or biological characteristics of air, land, water, or soil.

BOD (Biochemical Oxygen Demand)

The amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. High BOD indicates more pollution.

Eutrophication

The natural aging of a lake by nutrient enrichment of its water, often accelerated by human activities leading to algal blooms and oxygen depletion.

Biomagnification

Increase in concentration of the toxicant at successive trophic levels due to its non-degradability and accumulation in an organism.

Greenhouse Effect

Natural phenomenon where certain gases in the atmosphere (GHGs) trap heat, warming the Earth's surface and atmosphere. Essential for life, but enhanced effect leads to global warming.

Ozone Hole

Refers to the marked thinning of the ozone layer in the stratosphere, particularly over Antarctica, caused by ozone-depleting substances (ODS) like CFCs.

Acid Rain

Precipitation (rain, snow, fog) that is unusually acidic (pH < 5.6) due to atmospheric pollutants like sulfur dioxide (SO₂) and nitrogen oxides (NOₓ).

Electrostatic Precipitator (ESP)

A device used to remove particulate matter from the exhaust gases of industrial facilities by applying an electric field.

Air Pollution: Causes, Effects & Control

Air pollution is a major environmental issue caused by the presence of harmful substances in the atmosphere. These substances, known as pollutants, can be particulate (e.g., dust, soot, smoke) or gaseous (e.g., SO₂, NOₓ, CO, O₃). Major sources include vehicular emissions, industrial smoke, thermal power plants, and agricultural burning.

Harmful Effects:

• Respiratory Problems: Pollutants like particulate matter (PM2.5) can penetrate deep into lungs, causing asthma, bronchitis, emphysema, and lung cancer.
• Acid Rain: Sulfur dioxide and nitrogen oxides react with atmospheric water to form sulfuric and nitric acids, leading to acid rain which damages buildings, forests, and aquatic life.
• Global Warming: Greenhouse gases (CO₂, methane, N₂O) trap heat, contributing to global warming.
• Smog: Formation of photochemical smog (ground-level ozone, PAN) causes respiratory irritation and damages plants.

Control Measures:

• Electrostatic Precipitator (ESP): Widely used in thermal power plants to remove particulate matter. It works by charging the particles, which are then attracted to collecting plates.
• Scrubbers: Used to remove gaseous pollutants like SO₂. Water or a lime slurry is sprayed into the exhaust, reacting with the gas to remove it.
• Catalytic Converters: Fitted in automobiles to reduce emission of toxic gases. They convert unburnt hydrocarbons into CO₂ and H₂O, and carbon monoxide into CO₂, and nitric oxides into nitrogen gas and oxygen.
• BS-VI Norms: Stricter emission standards for vehicles.
• Switching to CNG: Compressed Natural Gas is a cleaner fuel for vehicles compared to petrol/diesel.

Comparing Key Water Pollution Indicators

Key Points to Remember for Exams

• Particulate Matter (PM2.5): Most harmful air pollutant, can cause respiratory and heart diseases.
• Noise Pollution: Measured in decibels (dB). Prolonged exposure > 80dB can cause hearing impairment, increased heartbeat, altered breathing.
• Solid Waste Management: Segregation at source, landfills (sanitary landfills are preferred), incineration, recycling, composting are key strategies. Focus on 'Reduce, Reuse, Recycle'.
• E-waste: Contains valuable metals (gold, copper, nickel) but also toxic substances (lead, mercury, cadmium). Proper recycling and disposal are crucial.
• Radioactive Waste: Extremely hazardous. Requires deep geological storage to prevent leakage and protect from radiation for thousands of years.
• Ozone Depletion: Primarily caused by Chlorofluorocarbons (CFCs) releasing chlorine atoms in the stratosphere, which catalytically break down ozone. Symptoms: increased UV-B radiation, skin cancer, cataracts, immune system damage.
• Montreal Protocol (1987): International treaty to phase out Ozone Depleting Substances (ODS).
• Greenhouse Gases (GHGs): CO₂, CH₄, N₂O, CFCs. CO₂ is the most significant contributor to global warming. Effects: sea level rise, extreme weather, loss of biodiversity.
• Deforestation: Causes include jhum cultivation, timber extraction, cattle ranching. Leads to soil erosion, desertification, loss of biodiversity, and contributes to global warming.
• Reforestation & Joint Forest Management (JFM): Key strategies for forest conservation. JFM involves local communities in forest protection and management.

Exam Tip: Case Studies and Mechanisms

For 'Environmental Issues', examiners often test your understanding of specific case studies (e.g., Chipko Movement, Amrita Devi Bishnoi, Arko-Jhum farming) and the mechanisms behind environmental phenomena (e.g., how CFCs deplete ozone, how biomagnification occurs, or the steps of eutrophication). Make sure to understand the 'why' and 'how' for each major issue and its solution. Practice explaining these mechanisms clearly and concisely.

Practice Questions with Solutions

• Q: What is the primary cause of ozone layer depletion, and what are its major consequences? A: The primary cause is Chlorofluorocarbons (CFCs). Major consequences include increased incidence of skin cancer, cataracts, damage to immune systems, and harm to plant life due to increased UV-B radiation.
• Q: Differentiate between biomagnification and bioaccumulation. A: Biomagnification is the increase in concentration of a toxicant at successive trophic levels in a food chain. Bioaccumulation is the build-up of a toxic substance in an organism's tissues over its lifetime, often from its environment.
• Q: Name two devices used to control particulate matter pollution and one for gaseous pollution. A: Particulate matter: Electrostatic Precipitator, Bag filter. Gaseous pollution: Scrubber (e.g., for SO₂).
• Q: What does a high BOD value in a water body indicate? A: A high BOD value indicates a high level of organic pollution in the water. This means there is a large amount of decomposable organic matter, requiring more oxygen for its breakdown by microorganisms, leading to oxygen depletion for aquatic life.

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