Chapter 5 — Environmental Issues (Botany) Exercise Solutions
Environmental biology questions often appear as 3-mark or 5-mark essay questions. Use clear headings and specific examples.
How to Use This Page
- Read the Key Concepts table first for a quick recap before attempting questions.
- Try each MCQ, Fill-in-the-Blank, and True/False on your own before checking answers.
- For 2-mark answers, write 3–5 sentences with one diagram or example.
- For 5-mark answers, use sub-headings, bullet points, and a labelled diagram where possible.
- Review the Common Mistakes section and Exam Checklist before your exam.
Key Concepts (Quick Recap)
| Term | Definition |
|---|---|
| Air pollution | Contamination of air by harmful gases (CO, SO₂, NOₓ) and particulate matter (SPM) from combustion and industries |
| Water pollution | Degradation of water quality by sewage, industrial effluents, and agricultural runoff |
| Soil pollution | Accumulation of pesticides, heavy metals, and plastics that reduce soil fertility |
| Noise pollution | Unwanted sound above 80 dB from traffic, industries, and crackers causing hearing loss and stress |
| Radioactive pollution | Ionising radiation from nuclear plants, X-rays, and radioactive waste causing cancer and mutations |
| Greenhouse effect | Trapping of heat by greenhouse gases (CO₂, CH₄, N₂O, CFCs, H₂O vapour) in the atmosphere |
| Global warming | Rise in Earth's average temperature due to increased greenhouse gas concentrations |
| Ozone depletion | Thinning of the stratospheric ozone layer by CFCs, increasing UV-B radiation reaching Earth |
| Eutrophication | Nutrient enrichment of water bodies leading to algal bloom, oxygen depletion, and aquatic death |
| BOD (Biochemical Oxygen Demand) | Amount of oxygen required by microbes to decompose organic matter in water; high BOD = polluted water |
| Deforestation | Removal of forest cover for agriculture, urbanisation, logging, and mining |
| Biodiversity hotspot | Region with high endemism and significant habitat loss; India has 4 such hotspots |
| In situ conservation | Protecting species in their natural habitat (sanctuaries, national parks, biosphere reserves) |
| Ex situ conservation | Protecting species outside their natural habitat (seed banks, zoos, botanical gardens) |
| Montreal Protocol (1987) | International treaty to phase out ozone-depleting substances (CFCs) |
I. Choose the Best Answer (MCQs)
1. Which of the following is the major greenhouse gas contributing to global warming? (a) O₂ (b) CO₂ (c) N₂ (d) Ar
2. BOD of a water sample indicates: (a) Dissolved oxygen content (b) Amount of heavy metals (c) Organic pollution level (d) Alkalinity
3. The Montreal Protocol (1987) is associated with: (a) Global warming (b) Acid rain (c) Ozone layer depletion (d) Deforestation
4. Eutrophication is caused by: (a) Oil spills (b) Heavy metals (c) Excess nitrates and phosphates (d) Pesticides
5. Which biodiversity hotspot in India includes the Western Ghats? (a) Western Ghats + Sri Lanka (b) Himalaya (c) Indo-Burma (d) Sundaland
6. The Kyoto Protocol (1997) aims to reduce: (a) Greenhouse gas emissions (b) Ozone-depleting substances (c) Mercury pollution (d) Plastic waste
7. Which of the following is an ex situ conservation method? (a) National park (b) Biosphere reserve (c) Seed bank (d) Wildlife sanctuary
8. CFCs cause ozone depletion by releasing: (a) Oxygen atoms (b) Nitrogen atoms (c) Chlorine atoms (d) Carbon atoms
9. Which pollutant causes blue baby syndrome (methemoglobinemia)? (a) CO (b) SO₂ (c) Nitrates (d) Lead
10. In situ conservation includes: (a) Zoos (b) Cryopreservation (c) Gene banks (d) Biosphere reserves
11. Acid rain is caused by: (a) CO₂ and CO (b) SO₂ and NOₓ (c) CFCs and CH₄ (d) O₃ and O₂
II. Fill in the Blanks
1. The full form of BOD is Biochemical Oxygen Demand. 2. The Montreal Protocol was signed in the year 1987. 3. CFCs stand for Chlorofluorocarbons. 4. Eutrophication leads to algal bloom and oxygen depletion / hypoxia in water bodies. 5. The Kyoto Protocol aims to reduce greenhouse gas emissions. 6. India has 4 biodiversity hotspots. 7. The ozone layer is found in the stratosphere (15–50 km altitude). 8. Afforestation is the process of planting trees in a deforested area. 9. The greenhouse gas most produced by rice paddies and cattle is methane (CH₄). 10. Cryopreservation is an example of ex situ conservation.
III. True or False (with corrections for false ones)
IV. Match the Following
| Column A | Column B |
|---|---|
| 1. Montreal Protocol | d. Ozone layer protection |
| 2. Kyoto Protocol | f. Greenhouse gas reduction |
| 3. BOD | a. Organic pollution in water |
| 4. Eutrophication | e. Nutrient enrichment of water |
| 5. CFCs | c. Ozone-depleting substances |
| 6. In situ conservation | g. Wildlife sanctuaries and national parks |
| 7. Ex situ conservation | b. Seed banks and cryopreservation |
| 8. Deforestation | h. Loss of biodiversity and carbon sink |
V. Answer Briefly (2-mark)
VI. Answer in Detail (5-mark)
Types of Pollution — Summary
| Type | Main Causes | Key Effects |
|---|---|---|
| Air | Combustion, industries | Smog, acid rain, respiratory diseases |
| Water | Sewage, fertilisers, oil spills | Eutrophication, BOD rise, disease |
| Soil | Pesticides, plastics, mining | Loss of soil biota, reduced fertility |
| Noise | Traffic, industries, crackers | Hearing loss, stress, hypertension |
| Radioactive | Nuclear plants, X-rays | Cancer, mutations, birth defects |
Greenhouse Gases and Global Warming
- Greenhouse gases: CO2, CH4, N2O, O3, CFCs, H2O vapour.
- CO2 is the major contributor (from fossil fuel combustion).
- Global warming → melting glaciers, rising sea level, altered rainfall.
- Kyoto Protocol (1997): International treaty to reduce GHG emissions.
Ozone Layer Depletion
- Ozone layer at stratosphere (15–50 km) absorbs harmful UV-B and UV-C.
- CFCs (chlorofluorocarbons) from refrigerants and aerosols catalytically destroy ozone.
- Thinning → increased UV radiation → skin cancer, cataracts, immune suppression.
- Montreal Protocol (1987): International treaty to phase out CFCs.
Deforestation — Causes and Effects
Causes: Agriculture expansion, logging, urbanisation, mining.
Effects:
- Loss of biodiversity
- Soil erosion and landslides
- Disruption of water cycle
- Climate change (loss of carbon sink)
- Tribal displacement
Biodiversity Hotspots in India
- India has 4 biodiversity hotspots: Western Ghats + Sri Lanka, Himalaya, Indo-Burma, Sundaland.
- Western Ghats — rich in endemic plants, amphibians, birds.
- Conservation: In situ (wildlife sanctuaries, national parks, biosphere reserves), Ex situ (seed banks, botanical gardens, zoos).
Worked Examples
Example 1 — BOD and water quality (model answer)
BOD (Biochemical Oxygen Demand) is the oxygen needed by microbes to break down organic matter in water. High BOD = more organic pollution and lower DO (Dissolved Oxygen). Clean water has low BOD and high DO.
Example 2 — Protocol → issue matching
Example 3 — Eutrophication (model answer)
Excess nutrients (nitrates, phosphates from fertilisers/sewage) enter a water body → algal bloom → algae die → microbes decompose them, consuming oxygen → DO falls → fish die. This nutrient-driven ageing of a lake is eutrophication.
Common Mistakes to Avoid
- ❌ Confusing BOD and DO — ✅ BOD is oxygen demanded by microbes; DO is oxygen available in water. High BOD = polluted, low DO = polluted.
- ❌ Saying Montreal Protocol is for global warming — ✅ Montreal Protocol is for ozone depletion; Kyoto Protocol is for greenhouse gases.
- ❌ Mixing up in situ and ex situ — ✅ In situ = in natural habitat (national parks); Ex situ = outside habitat (seed banks, zoos).
- ❌ Writing "CFCs release fluorine" — ✅ CFCs release chlorine atoms that destroy ozone.
- ❌ Stating energy pyramid can be inverted — ✅ Energy pyramid is always upright; only biomass and number pyramids can be inverted.
- ❌ Confusing eutrophication cause — ✅ Eutrophication is caused by excess nitrates and phosphates, not by oil spills or heavy metals.
- ❌ Forgetting to name all 4 Indian biodiversity hotspots — ✅ Western Ghats + Sri Lanka, Himalaya, Indo-Burma, Sundaland.
- ❌ Saying BOD measures dissolved oxygen — ✅ BOD measures oxygen consumed by microbes; DO measures oxygen present in water.
Common Mistakes
- Confusing BOD (Biological Oxygen Demand) and DO (Dissolved Oxygen) — high BOD means polluted, low DO means polluted.
- Not specifying the protocol (Montreal for ozone, Kyoto for CO2) in exam answers.
- Mixing up in situ and ex situ conservation definitions.
Exam Checklist
- Know all types of pollution (air, water, soil, noise, radioactive) with specific examples
- List all greenhouse gases (CO₂, CH₄, N₂O, CFCs, H₂O vapour) and their sources
- Distinguish Montreal Protocol (ozone) from Kyoto Protocol (global warming)
- Explain eutrophication step by step with labelled diagram description
- Define BOD and relate it to water quality (high BOD = polluted)
- Name all 4 biodiversity hotspots in India
- Differentiate in situ and ex situ conservation with 2 examples each
- Describe CFC mechanism: CFCs → UV breaks them → chlorine atoms → catalytic ozone destruction
- List causes and effects of deforestation with control measures
- Explain the greenhouse effect and its consequences
- Draw the trophic transfer of energy (10% law) and state why energy pyramid is always upright
- Know key terms: eutrophication, BOD, CFCs, biodiversity hotspot, cryopreservation