Environmental Issues

NCERT Line-by-Line Breakdown for NEET 2026

Unit 5: Ecology and Environment

Human population explosion has led to a tremendous demand for food, water, home, electricity, roads, and automobiles. This exerts pressure on natural resources and causes Pollution (undesirable change in physical, chemical, or biological characteristics of air, land, water, or soil).

Government of India Act: The Environment (Protection) Act, 1986 was passed to protect and improve the quality of our environment.

1. Air Pollution and Its Control

Control Methods

Device	Target Pollutant	Mechanism
Electrostatic Precipitator (ESP)	Particulate Matter (Removes >99%).	Electrode wires release electrons (corona) → dust gets charged (-ve) → attracted to collection plates (+ve).
Scrubber	Gases like SO₂.	Exhaust passes through spray of water or lime.
Catalytic Converter	Hydrocarbons, CO, NO.	Metals (Pt, Pd, Rh) convert unburnt HC to CO₂ + H₂O; CO to CO₂; NO to N₂. (Unleaded petrol is essential as lead inactivates the catalyst).

[Image of electrostatic precipitator diagram]

Important Acts:

Air (Prevention and Control of Pollution) Act: Came into force in 1981.
Amendment (1987): Included NOISE as an air pollutant.

Case Study: Delhi (CNG)

In the 1990s, Delhi ranked 4th among most polluted cities. SC ordered public transport to switch to CNG (Compressed Natural Gas) by 2002.
Advantages of CNG: Burns efficiently, cheaper than petrol/diesel, cannot be siphoned/adulterated.

2. Water Pollution and Its Control

Water (Prevention and Control of Pollution) Act: 1974.

A. Domestic Sewage & BOD

Even 0.1% impurities make water unfit. Sewage contains biodegradable organic matter.
BOD (Biochemical Oxygen Demand): Amount of O₂ consumed by microbes to oxidize organic matter. High BOD = High Pollution = Low Dissolved Oxygen (DO) → Fish mortality.

B. Algal Bloom

Excess nutrients (N, P) cause excessive growth of planktonic algae. Imparts color to water, deteriorates water quality, toxic to animals. Example: Eichhornia crassipes (Terror of Bengal).

C. Biomagnification

Increase in concentration of toxicant at successive trophic levels. (Toxic substance cannot be metabolized/excreted).

Example (DDT):
Water (0.003 ppb) → Zooplankton (0.04 ppm) → Small Fish (0.5 ppm) → Large Fish (2 ppm) → Fish-eating Birds (25 ppm).
Effect: Disturbs Calcium metabolism in birds → Thinning of eggshells → Premature breaking → Decline in bird population.

D. Eutrophication

Natural aging of a lake by nutrient enrichment.

Natural: Takes thousands of years.
Cultural/Accelerated: Caused by human activities (sewage, agricultural runoff). Lake gets choked with algae/plants, becomes shallower and warmer.

3. Solid & Radioactive Wastes

Solid Wastes

Sanitary Landfills: Wastes dumped in depression/trench and covered with dirt. Problem: Seepage of chemicals (leachate) polluting groundwater.
Polyblend Case Study (Ahmed Khan): Plastic sack manufacturer in Bangalore developed Polyblend (fine powder of recycled plastic). Mixed with bitumen to lay roads. Roads last 3x longer.

Radioactive Wastes

Most potent pollutant. Problems: (1) Accidental leakage (Chernobyl, Three Mile Island), (2) Safe disposal.
Effect: Mutations (Cancer), Lethal in high doses.
Disposal: Buried in shielded containers 500m deep below earth’s surface.

4. Greenhouse Effect & Ozone Depletion

A. Greenhouse Effect

Naturally occurring phenomenon responsible for heating Earth’s surface and atmosphere. Without it, Earth’s temp would be -18°C (current avg is 15°C).

Global Warming: Increase in Earth’s temp due to enhanced greenhouse effect.

[Image of greenhouse gases contribution pie chart]

Greenhouse Gases (GHGs): CO₂ (60%), CH₄ (20%), CFCs (14%), N₂O (6%).
El Nino Effect: Climatic change leading to melting of polar ice caps.

B. Ozone Depletion

Good Ozone: Stratosphere (Shields UV).
Bad Ozone: Troposphere (Pollutant).
Measurement: Dobson Units (DU).

Mechanism: CFCs (Chlorofluorocarbons) move to stratosphere → UV breaks them releasing Cl atoms → Cl acts as catalyst converting Ozone (O₃) to Oxygen (O₂) → Ozone depletion (Ozone Hole over Antarctica).

Montreal Protocol (1987): Signed at Montreal (Canada) to control emission of Ozone Depleting Substances (ODS).

5. Deforestation & People’s Participation

Jhum Cultivation (Slash and Burn): North-eastern states. Farmers cut down trees, burn remains (ash = fertilizer), use land for farming, then leave it for recovery. Problem: Recovery phase shortened due to population pressure.
Reforestation: Restoring a forest that once existed.

Case Studies of Conservation

Bishnoi Community (1731): Amrita Devi Bishnoi hugged trees to protect them from King’s men in Jodhpur. (Amrita Devi Bishnoi Wildlife Protection Award instituted).
Chipko Movement (1974): Garhwal Himalayas. Local women showed bravery in protecting trees.
Joint Forest Management (JFM, 1980s): Government works closely with local communities for protecting and managing forests.

📝 Rapid Fire MCQs

Q1. Which of the following is the most significant greenhouse gas contributing to global warming?

A) Methane
B) CFCs
C) Carbon dioxide
D) Nitrous oxide

Click to check Answer

Answer: C) Carbon dioxide (60% contribution).

Q2. The Montreal Protocol was signed in 1987 to control:

A) Emission of Greenhouse gases
B) Emission of Ozone depleting substances
C) Disposal of e-wastes
D) Release of genetically modified organisms