CBSE Class 12 Biology Long Answer Questions – Environmental Issues (NCERT Based)

Unit V: Ecology and Environment | Chapter 16: Environmental Issues

CBSE Class 12 Biology Chapter 16 Long Answer Questions – Environmental Issues (NCERT)

Course & Examination Details

• Course: CBSE Class 12 Biology
• Unit: Unit V – Ecology and Environment
• Chapter: Chapter 16 – Environmental Issues
• Board: Central Board of Secondary Education (CBSE)
• Syllabus Base: Strictly as per NCERT Textbook
• Exam Relevance: CBSE Class 12 Board Examinations (5-Mark Questions)

Long Answer Type Questions (120–150 Words Each)

(Prepared strictly according to NCERT syllabus with clear structure and exam-oriented presentation)

Section A: Air Pollution and Its Control (Q1–Q6)

Q1. Define air pollution. Describe its major sources and effects on human health.

Ans:
Air pollution is the presence of harmful substances such as gases, particulates, and biological molecules in the atmosphere at concentrations that adversely affect living organisms and property. Major sources include automobile exhausts, industrial emissions, thermal power plants, and burning of fossil fuels. Pollutants like carbon monoxide reduce oxygen transport in blood, while sulphur dioxide and nitrogen oxides cause respiratory disorders. Particulate matter penetrates deep into lungs, leading to asthma, bronchitis, and cardiovascular diseases. Prolonged exposure increases risk of lung cancer and reduces life expectancy, making air pollution a serious public health concern.

Q2. Explain the formation of acid rain and its environmental consequences.

Ans:
Acid rain is formed when sulphur dioxide and nitrogen oxides released from industries and vehicles react with atmospheric moisture to produce sulphuric and nitric acids. These acids fall as rain, snow, or dry deposition. Acid rain lowers soil pH, leaches essential nutrients, damages crops, and affects forest vegetation. In aquatic ecosystems, it reduces pH of water bodies, causing fish mortality. Acid rain also corrodes buildings and historical monuments, especially those made of marble and limestone, such as the Taj Trapezium region.

Q3. Describe various methods used to control air pollution.

Ans:
Air pollution can be controlled using both preventive and corrective measures. Cleaner fuels such as CNG and LPG reduce emissions. Industries use electrostatic precipitators and scrubbers to remove particulate matter. Automobiles are fitted with catalytic converters to convert harmful gases into less toxic substances. Afforestation helps absorb pollutants and improve air quality. Strict enforcement of emission standards and promotion of renewable energy sources also play an important role in long-term air pollution control.

Q4. What is photochemical smog? Explain its causes and effects.

Ans:
Photochemical smog is a brownish haze formed when nitrogen oxides and hydrocarbons react in the presence of sunlight. It commonly occurs in urban areas with heavy vehicular traffic. Ozone, a major component of smog, irritates eyes, damages lung tissue, and affects crop productivity. Smog reduces visibility and causes respiratory discomfort. Continuous exposure leads to chronic health issues, making photochemical smog a major urban environmental problem.

Q5. Explain the role of catalytic converters in controlling automobile pollution.

Ans:
Catalytic converters are devices fitted in vehicle exhaust systems to reduce harmful emissions. They convert carbon monoxide into carbon dioxide, nitrogen oxides into nitrogen, and hydrocarbons into carbon dioxide and water. These reactions significantly lower toxic emissions from vehicles. Use of unleaded petrol is necessary to prevent damage to catalysts. Catalytic converters are effective tools in reducing urban air pollution.

Q6. How does air pollution contribute to global environmental problems?

Ans:
Air pollution releases greenhouse gases such as carbon dioxide and methane, enhancing the greenhouse effect and causing global warming. Sulphur dioxide and nitrogen oxides cause acid rain, damaging ecosystems. Ozone-depleting substances thin the ozone layer, increasing UV radiation exposure. Thus, air pollution contributes to climate change, biodiversity loss, and environmental degradation on a global scale.

Section B: Water Pollution and Solid Waste Management (Q7–Q12)

Q7. Define water pollution and explain its major sources.

Ans:
Water pollution refers to contamination of water bodies by harmful substances that degrade water quality and harm aquatic life. Major sources include domestic sewage, industrial effluents, agricultural runoff containing fertilizers and pesticides, and oil spills. Untreated sewage increases organic load and depletes dissolved oxygen. Industrial wastes may contain heavy metals and toxic chemicals, making water unsafe for consumption and aquatic organisms.

Q8. Explain eutrophication and its impact on aquatic ecosystems.

Ans:
Eutrophication is nutrient enrichment of water bodies due to excess nitrates and phosphates from agricultural runoff. It leads to excessive algal growth, forming algal blooms. These blooms reduce light penetration and dissolved oxygen levels when algae decompose. Oxygen depletion causes death of fish and other aquatic organisms, disrupting the ecosystem balance.

Q9. Describe methods used to control water pollution.

Ans:
Water pollution can be controlled by treating sewage and industrial effluents before discharge. Use of biodegradable detergents and controlled application of fertilizers reduce pollution. Prevention of oil spills and proper waste disposal also help maintain water quality. Strict environmental regulations are essential for sustainable water management.

Q10. What is solid waste management? Explain its importance.

Ans:
Solid waste management involves collection, segregation, treatment, and safe disposal of waste. It is important to prevent land and water pollution, control disease spread, and conserve resources. Methods include composting, recycling, sanitary landfills, and incineration. Proper waste management promotes environmental sustainability and public health.

Q11. Explain composting and recycling as waste management strategies.

Ans:
Composting involves microbial decomposition of biodegradable waste into manure, improving soil fertility. Recycling converts waste materials like paper, glass, and plastics into reusable products, conserving natural resources and reducing pollution. Both methods reduce landfill burden and promote sustainable waste management.

Q12. Discuss the environmental hazards of e-waste.

Ans:
E-waste contains toxic substances like lead, mercury, and cadmium. Improper disposal contaminates soil and water, causing health hazards. Recycling e-waste safely helps reduce environmental and human health risks.

Section C: Agrochemicals and Radioactive Wastes (Q13–Q17)

Q13. What are agrochemicals? Discuss their harmful effects.

Ans:
Agrochemicals include fertilizers, pesticides, and herbicides used to increase crop yield. Excessive use degrades soil fertility, pollutes water bodies, and causes biomagnification of toxins. They harm non-target organisms and disrupt ecosystems.

Q14. Explain biomagnification with a suitable example.

Ans:
Biomagnification is the progressive increase in concentration of toxic substances at successive trophic levels. For example, DDT accumulates in fish and reaches higher concentration in fish-eating birds, causing reproductive failure.

Q15. What are radioactive wastes? Explain their hazards.

Ans:
Radioactive wastes originate from nuclear power plants and medical uses. They cause genetic mutations, cancer, and long-term environmental contamination due to prolonged radioactivity.

Q16. Describe safe disposal methods of radioactive wastes.

Ans:
Radioactive wastes are sealed and stored in deep geological repositories to prevent leakage. Shielding and strict monitoring ensure environmental safety.

Q17. Why are radioactive wastes more dangerous than other wastes?

Ans:
They remain radioactive for long periods and can cause irreversible genetic damage, making them extremely hazardous.

Section D: Climate Change, Ozone Depletion and Deforestation (Q18–Q25)

Q18. Explain greenhouse effect and its role in global warming.

Ans:
The greenhouse effect traps heat in the atmosphere due to gases like CO₂ and methane. Excessive greenhouse gases enhance this effect, leading to global warming.

Q19. Discuss the major effects of global warming.

Ans:
Global warming causes melting of glaciers, sea-level rise, extreme weather events, and biodiversity loss, threatening ecosystems and human settlements.

Q20. What measures can be taken to control global warming?

Ans:
Reducing fossil fuel use, adopting renewable energy, afforestation, and energy efficiency can control global warming.

Q21. Explain ozone depletion and its consequences.

Ans:
Ozone depletion occurs due to CFCs, increasing UV radiation exposure. It causes skin cancer, eye disorders, and reduced crop productivity.

Q22. What steps are taken to prevent ozone depletion?

Ans:
Banning CFCs and using ozone-friendly alternatives help protect the ozone layer.

Q23. Define deforestation and explain its causes.

Ans:
Deforestation is large-scale removal of forests for agriculture, urbanization, and mining. It is driven by population growth and industrialization.

Q24. Discuss the environmental effects of deforestation.

Ans:
Deforestation causes biodiversity loss, soil erosion, climate change, and disruption of water cycles.

Q25. How can deforestation be controlled?

Ans:
Afforestation, sustainable forest management, and social forestry help control deforestation and conserve ecosystems.

CBSE Board Exam Tip

These long answer questions (5 marks) are ideal for CBSE Class 12 board exams, focusing on definitions, causes, effects, and control measures, strictly aligned with NCERT Chapter 16 – Environmental Issues.