Environmental Issues is the closing Class 12 ecology chapter that covers how human activity pollutes air, water and land, and the laws, devices and people’s movements that fight back. It packs in air and water pollution control (ESP, scrubbers, BOD, eutrophication), solid, radioactive and thermal waste, the greenhouse effect and global warming, ozone depletion, and deforestation case studies. It is a high-yield, fact-heavy NEET chapter where exact names, years and percentages decide marks.
Class 12 Biology · Chapter 16 – swipe through all 8 cards to understand the whole chapter.
Environmental Issues
How human activity pollutes air, water and land, and the laws/movements that fight back.
High-yield, fact-heavy NEET chapter — names, years and percentages matter.
- Match each pollutant to its control device or law
- Year traps: Water Act 1974, Air Act 1981, Montreal 1987
- Lock the name-pairs (Chipko, Bishnoi, Ahmed Khan)
Air Pollution & Its Control
Two different cleaners are needed: one for solid particles, one for gases.
Air (Prevention & Control of Pollution) Act, 1981.
- ESP charges dust → grounded plates collect it (>99% removed)
- Catalytic converter (Pt-Pd-Rh): HC→CO2+H2O, CO+NO→CO2+N2; needs unleaded petrol
- PM 2.5 (≤2.5 μm) reaches alveoli; CNG burns cleaner (Delhi buses)
Water Pollution, BOD & Eutrophication
Organic waste makes microbes use up oxygen; nutrients trigger algal blooms.
Water (Prevention & Control of Pollution) Act, 1974.
- BOD = O2 bacteria need to break down organic matter; clean water = low BOD
- Eutrophication: N + P run-off → algal bloom → light blocked + O2 crash → death
- Biomagnification: DDT/mercury rise up food chain; DDT thins birds’ eggshells
Solid, Radioactive & Thermal Waste
Sort waste first, then dispose smartly — four very different leftovers.
Ahmed Khan (Bangalore) → polyblend + bitumen = durable plastic roads.
- Sanitary landfill (pit covered with soil) replaced open dumping
- E-waste exported to India, China, Pakistan; only metals recoverable
- Radioactive: mutation at high dose, cancer at low dose; thermal pollution lowers dissolved O2
Greenhouse Effect & Global Warming
Greenhouse gases let sunlight in but trap re-radiated infrared, warming Earth.
CH4 most potent per molecule; CO2 biggest total — keep these separate.
- Natural effect keeps Earth warm; excess gases cause global warming
- Effects: polar ice/glacier melt, sea-level rise, El Niño, odd weather
- Controls: cut fossil fuels, plant trees, slow population growth
Ozone Depletion in the Stratosphere
Same molecule O3 — a shield up high, a pollutant down low.
Good ozone = stratosphere; bad ozone = troposphere. Measured in Dobson Units (DU).
- CFCs drift up; UV releases Cl atoms that destroy ozone catalytically
- Ozone hole = seasonal thinning over Antarctic; UV-B → DNA damage, skin cancer, cataract
- Montreal Protocol (1987) limits CFCs (≠ Kyoto = greenhouse gases)
Deforestation & Restoration
Cutting forests unplugs the carbon sponge, soil grip and water cycle at once.
JFM = government works WITH local communities.
- Causes: agriculture, slash-and-burn (jhum), timber/fuel, ranching
- Effects: CO2 rise, biodiversity loss, soil erosion, desertification
- Chipko (Garhwal) · Amrita Devi Bishnoi (Khejri, Rajasthan) · JFM (community + govt)
Laws, Years & Name-Pairs
The exam-favourite facts that win or lose marks in one line each.
Don’t swap ESP/scrubber, BOD logic, good/bad ozone, or tropical/temperate loss.
- ESP = particles, scrubber = gases; catalyst metals = Pt, Pd, Rh
- High BOD = dirty; biomagnification = toxin rises up trophic levels
- Chipko = hug trees; Bishnoi = Khejri; Ahmed Khan = polyblend roads
📝 Practice Environmental Issues — 10 NEET PYQs
Real previous-year questions · with answers & solutions
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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
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Frequently Asked Questions
It covers air pollution and its control, water pollution along with BOD and eutrophication, solid, radioactive and thermal waste management, the greenhouse effect and global warming, ozone layer depletion, and deforestation with restoration case studies. It is the final ecology chapter in the Class 12 NCERT syllabus.
BOD (Biochemical Oxygen Demand) is the amount of oxygen that bacteria need to break down the organic matter in a water sample. A high BOD means more organic pollution and dirtier, oxygen-poor water, while clean water has a low BOD.
Yes, it is a high-yield, fact-heavy chapter that regularly contributes direct NCERT-line questions. Focus on memorising the laws and years (Water Act 1974, Air Act 1981, Montreal Protocol 1987), control devices, and name-pairs like Chipko, Bishnoi and Ahmed Khan.
Good ozone lies in the upper atmosphere (stratosphere) and shields us by absorbing harmful UV radiation, while bad ozone forms in the lower atmosphere (troposphere) and acts as a pollutant that harms plants and animals. It is the same molecule, O3, but its location decides whether it protects or harms.
An electrostatic precipitator (ESP) removes over 99 percent of solid particulate matter by charging the dust particles so they collect on grounded plates, whereas a scrubber removes gases such as SO2 by passing the exhaust through a water or lime spray. ESP handles particles and the scrubber handles gases.