Class 12 Biology Chapter 16 Environmental Issues Notes
16.1 Air Pollution and Its Control
Air pollution refers to the presence of harmful substances in the atmosphere that adversely affect living organisms and the environment.
Sources of Air Pollution
Automobile exhaust (CO, NOx, hydrocarbons)
Industrial emissions
Burning of fossil fuels
Use of CFCs and aerosols
Control Measures
Use of CNG and unleaded petrol
Installation of catalytic converters
Strict pollution control laws
Afforestation and green belts
Adoption of Euro emission norms
16.2 Water Pollution and Its Control
Domestic Sewage – Constituents
Domestic sewage contains four main types of impurities:
Suspended solids
Sand, silt, soil particles
Colloidal particles
Faecal matter, bacteria, paper, cloth
Dissolved solids
Nitrates, phosphates, ammonia, calcium, sodium
Pathogens
Disease-causing microbes (cholera, typhoid, dysentery)
Effects of Sewage Discharge into Rivers
Eutrophication
Increase in BOD (Biochemical Oxygen Demand)
Growth of pathogenic bacteria
Destruction of aquatic flora and fauna
Gradual ageing and silting of rivers
16.3 Solid Wastes
Types of Solid Waste
Household: food waste, plastics, paper, cloth
School: paper, chalk, plastic
Trips/public places: disposable cups, plates, food waste
Waste Reduction
Difficult to reduce biodegradable waste completely
Possible steps:
Reduce food wastage
Reuse and recycle plastics, paper, metals
Segregation of biodegradable and non-biodegradable waste
16.4 Agro-chemicals and Their Effects
Excessive use of fertilisers and pesticides leads to:
Soil pollution
Water contamination
Biomagnification
Health hazards to humans and animals
16.5 Radioactive Wastes
Radioactive Waste
Generated from:
Nuclear reactors
Medical radiation therapy
Mining of radioactive elements
Harmful Effects
Cancer
Birth defects
Genetic mutations
Infertility
👉 Radioactive waste is one of the most dangerous pollutants.
16.6 Greenhouse Effect and Global Warming
Greenhouse Gases (GHGs)
CO₂, CH₄, N₂O, CFCs
Causes of Global Warming
Increased fossil fuel combustion
Deforestation
Automobile emissions
Use of CFCs
Industrialisation
Effects of Global Warming
Rise in global temperature
Melting of polar ice caps
Sea level rise
Loss of biodiversity
Droughts and floods
Change in rainfall pattern
Control Measures
Use of renewable energy (solar, wind)
Afforestation
Reduced use of nitrogen fertilisers
Substitutes for CFCs
16.7 Ozone Depletion in the Stratosphere
Why Ozone Hole Forms Over Antarctica?
Presence of CFCs
Extremely low temperature (–85°C)
Formation of ice clouds
Polar vortex isolates air
Ozone destruction occurs during spring
Effects of Enhanced UV-B Radiation
Skin cancer
Cataract and blindness
Weak immune system
Increased mutation rate
Reduced photosynthesis in phytoplankton
16.8 Degradation by Improper Resource Utilisation
Groundwater Depletion
Excessive pumping lowers water table
Leads to drying of wells
Increased cost of water extraction
Replenishment Measures
Rainwater harvesting
Afforestation
Controlled groundwater use
16.9 Deforestation
Role of Women and Communities
Bishnoi movement (Amrita Devi sacrifice)
Chipko movement – hugging trees to prevent cutting
Community participation ensures sustainable conservation
16.10 Waste Management Issues
(a) Eutrophication
Excess nutrients → algal bloom
Oxygen depletion → death of aquatic life
(b) Biological Magnification
Increase in concentration of toxic substances at higher trophic levels
Example: DDT
(c) Municipal Solid Waste
Household garbage
Managed by:
Source reduction
Recycling
Composting
(d) Defunct Ships and E-waste
Contain toxic materials (asbestos, mercury)
Health risk to workers
Recycling is the only sustainable solution
Initiatives to Reduce Vehicular Pollution in Delhi
Introduction of CNG
Catalytic converters
Unleaded fuel
Euro-II norms
Removal of old vehicles
👉 Result: Significant improvement in air quality
Important Terms (Exam Focus 🔥)
Greenhouse gases: Trap heat in atmosphere
Catalytic converter: Converts CO, NOx into harmless gases
UV-B radiation: Causes skin cancer and ecological damage
16.10 Summary (One-Look Revision)
Pollution affects air, water, soil and life
Sewage causes eutrophication and BOD increase
Solid waste needs proper management
Global warming and ozone depletion are global threats
Community participation is crucial
Sustainable development is the only solution
✍️ Top 10 Short Question–Answers
Q1. What is air pollution?
Answer: Presence of harmful substances in air that adversely affect living organisms and environment.
Q2. Name any one major source of air pollution.
Answer: Automobile exhaust.
Q3. What is BOD?
Answer: Biochemical Oxygen Demand; indicates organic pollution in water.
Q4. What is eutrophication?
Answer: Nutrient enrichment of water bodies leading to algal bloom and oxygen depletion.
Q5. Name any one greenhouse gas.
Answer: Carbon dioxide (CO₂).
Q6. What is biomagnification?
Answer: Increase in concentration of toxic substances at higher trophic levels.
Q7. What causes ozone depletion?
Answer: Chlorofluorocarbons (CFCs).
Q8. Name one harmful effect of UV-B radiation.
Answer: Skin cancer.
Q9. What is groundwater depletion?
Answer: Lowering of water table due to excessive pumping.
Q10. Name one people’s movement against deforestation.
Answer: Chipko movement.
📝 Long Answer Questions
Q1. Explain air pollution and its control measures.
Answer:
Air pollution occurs due to harmful gases and particulates in the atmosphere.
Sources:
Automobile exhaust
Industrial emissions
Burning of fossil fuels
CFCs and aerosols
Control measures:
Use of CNG and unleaded petrol
Catalytic converters
Pollution control laws
Afforestation and green belts
Euro emission norms
Q2. Describe water pollution due to domestic sewage.
Answer:
Domestic sewage contains:
Suspended solids (sand, silt)
Colloidal particles (faecal matter, bacteria)
Dissolved solids (nitrates, phosphates)
Pathogens
Effects:
Eutrophication
Increase in BOD
Growth of pathogenic bacteria
Death of aquatic organisms
Q3. Explain greenhouse effect and global warming.
Answer:
Greenhouse effect is the trapping of heat by greenhouse gases.
Greenhouse gases: CO₂, CH₄, N₂O, CFCs
Causes of global warming:
Fossil fuel combustion
Deforestation
Industrialisation
Effects:
Rise in global temperature
Melting of ice caps
Sea level rise
Loss of biodiversity
Control measures:
Renewable energy
Afforestation
Reduced fertiliser use
Substitutes for CFCs
📝 PYQs (Previous Year Questions)
🔹 1️⃣ Very Short Answer Questions (1 Mark)
What is air pollution?
Name one major source of air pollution in cities.
What is BOD?
Define eutrophication.
Name any one greenhouse gas.
What is biomagnification?
Name the chemical responsible for ozone depletion.
What is the ozone hole?
Name one harmful effect of UV-B radiation.
Name one movement against deforestation in India.
🔹 2️⃣ Short Answer Questions (2–3 Marks)
What are the sources of air pollution?
Write any two measures to control air pollution.
What are the constituents of domestic sewage?
Explain eutrophication.
What is solid waste? Mention two methods of waste management.
Write any two harmful effects of excessive use of agro-chemicals.
What is radioactive waste? Mention its harmful effects.
What are greenhouse gases?
What is groundwater depletion?
What is biological magnification? Give one example.
🔹 3️⃣ Long Answer Questions (3–5 Marks)
Explain air pollution and its control measures.
Describe water pollution caused by domestic sewage.
Explain greenhouse effect and global warming.
Describe causes and effects of ozone depletion.
What are the effects of radioactive wastes on living organisms?
Explain deforestation and role of people’s movements in forest conservation.
Describe solid waste management and its importance.
🔹 4️⃣ Difference-Based PYQs (Very Important)
Air pollution vs Water pollution
Global warming vs Ozone depletion
Eutrophication vs Biomagnification
Biodegradable waste vs Non-biodegradable waste
Renewable resources vs Non-renewable resources
🔹 5️⃣ Assertion–Reason / Concept-Based PYQs
Domestic sewage increases BOD of water bodies. Explain.
Ozone depletion is more severe over Antarctica. Give reason.
Biomagnification affects top consumers the most. Justify.
Use of CNG reduces vehicular pollution. Explain.
Community participation is essential for environmental conservation. Justify.
🔹 6️⃣ Diagram / Flowchart Based PYQs
Diagram showing greenhouse effect.
Diagrammatic representation of eutrophication.
Flowchart showing solid waste management.
Diagram showing ozone depletion process.
❓ FAQs (5)
FAQ 1. Why is radioactive waste dangerous?
It causes cancer, genetic mutations and birth defects.
FAQ 2. Why does ozone hole form over Antarctica?
Due to CFCs, very low temperature and polar vortex.
FAQ 3. How can groundwater depletion be controlled?
By rainwater harvesting and afforestation.
FAQ 4. What is the role of community in forest conservation?
Movements like Chipko and Bishnoi prevent deforestation.
FAQ 5. Why is sustainable development necessary?
To meet present needs without harming future generations.
| Chapter No. | Chapter Name | Visit |
|---|---|---|
| 1 | Reproduction in Organisms | Visit |
| 2 | Sexual Reproduction in Flowering Plants | Visit |
| 3 | Human Reproduction | Visit |
| 4 | Reproductive Health | Visit |
| 5 | Principles of Inheritance and Variation | Visit |
| 6 | Molecular Basis of Inheritance | Visit |
| 7 | Evolution | Visit |
| 8 | Human Health and Disease | Visit |
| 9 | Strategies for Enhancement in Food Production | Visit |
| 10 | Microbes in Human Welfare | Visit |
| 11 | Biotechnology: Principles and Processes | Visit |
| 12 | Biotechnology and its Applications | Visit |
| 13 | Organisms and Populations | Visit |
| 14 | Ecosystem | Visit |
| 15 | Biodiversity and Conservation | Visit |
| 16 | Environmental Issues | Visit |
0 Comments