Chapter 22 — Environmental Issues (Zoology) Exercise Solutions
This chapter focuses on environmental problems from a Zoology perspective — effects on animals and human health. Link to Chapter 5 (Botany) concepts.
How to Use This Page
1. Start with the Key Concepts table — quickly revise definitions before attempting questions. 2. Work through the exercise sections in order — MCQs, Fill in the Blanks, True or False, Match the Following, then short and long answers. 3. Read the Worked Examples for model answer format and depth expected by examiners. 4. Check the Common Mistakes section — these are the most frequent errors students make in board exams. 5. Use the Exam Checklist before your exam to ensure you have covered every high-yield topic.
Key Concepts (Quick Recap)
| Term | Definition |
|---|
| Biomagnification | Progressive increase in concentration of a substance along the food chain, especially fat-soluble pollutants |
| Bioaccumulation | Accumulation of a substance within a single organism over its lifetime |
| Minamata disease | Neurological disorder caused by methylmercury poisoning, first identified in Minamata Bay, Japan (1956) |
| Greenhouse effect | Trapping of outgoing infrared radiation by greenhouse gases (CO₂, CH₄, N₂O, CFCs), warming the atmosphere |
| Acid rain | Rain with pH below 5.6, caused by SO₂ and NOₓ reacting with atmospheric water |
| E-waste | Discarded electronic devices containing toxic materials like lead, cadmium, mercury, and brominated flame retardants |
| Photochemical smog | Formed by reaction of NOₓ and hydrocarbons in sunlight, producing ozone and peroxides at ground level |
| Carboxyhaemoglobin | Compound formed when CO binds haemoglobin (200× stronger affinity than O₂), reducing oxygen transport |
| Thermal pollution | Rise in water temperature from industrial cooling discharge, reducing dissolved oxygen and harming aquatic life |
| Itai-itai disease | Cadmium poisoning causing severe bone pain and fractures, first identified in Toyama, Japan |
| Particulate matter (PM2.5) | Fine particles ≤2.5 μm that penetrate deep into lungs, causing respiratory and cardiovascular disease |
| Ozone depletion | Thinness of stratospheric ozone layer caused by CFCs, increasing UV-B radiation reaching Earth |
| BOD (Biochemical Oxygen Demand) | Amount of dissolved oxygen required by microorganisms to decompose organic matter in water |
| Eutrophication | Excessive nutrient enrichment of water bodies causing algal blooms and oxygen depletion |
Major Pollutants and Their Effects
| Pollutant | Source | Effect on Animals/Humans |
|---|
| CO | Vehicles, incomplete combustion | Binds Hb → carboxyhaemoglobin → suffocation |
| SO2 | Power plants, industries | Acid rain, respiratory disease, vegetation damage |
| NOx | Vehicles, industry | Photochemical smog, acid rain |
| Lead | Old paint, vehicle exhaust, mining | Neurotoxicity, reduced IQ in children |
| Mercury | Industries, mining, fish | Minamata disease (neurological damage) |
| DDT | Pesticide | Biomagnification, eggshell thinning in birds |
| Plastic | Consumer waste | Entanglement, ingestion by wildlife |
Biomagnification — Mechanism
Persistent fat-soluble organic pollutants (DDT, PCBs, mercury) are not metabolised — they accumulate in fat tissue. Each consumer at higher trophic level consumes many prey individuals, concentrating the substance further.
DDT concentration example:
- Water → Algae → Zooplankton → Small fish → Large fish → Fish-eating bird
- Concentration increases 1000–10,000 fold from base to top
Impact: Eggshell thinning in raptors (eagles, ospreys, peregrine falcon) → reproductive failure → population crash.
Radioactive Pollution
Sources: Nuclear power plants, nuclear weapon testing, X-ray equipment, radioactive mining.
Effects:
- DNA damage → mutations, cancer
- Bone marrow damage → reduced blood cell production
- Foetal abnormalities
- Long-lived isotopes (Cs-137, Sr-90) persist for decades
Chernobyl (1986) and Fukushima (2011) — nuclear disasters with lasting ecological effects.
E-Waste (Electronic Waste)
- Old computers, phones, circuit boards contain toxic materials: lead, cadmium, mercury, chromium, brominated flame retardants.
- Informal recycling in developing countries → direct exposure → serious health risks.
- India's E-Waste Management Rules (2016) regulate disposal.
Water Pollution and Aquatic Life
- Oil spills: Coat feathers of seabirds (reduces insulation, buoyancy) → death; coat gills of fish → suffocation.
- Thermal pollution: Hot water from power plant cooling reduces dissolved oxygen in rivers → fish kills.
- Acid rain: pH drops in lakes → aluminium ions mobilised → toxic to fish; shell dissolution in molluscs.
- Plastic in oceans: Microplastics ingested by zooplankton, fish, seabirds, marine mammals.
Noise Pollution Effects
- Hearing loss (above 80 dB chronic exposure)
- Physiological stress (increased cortisol, hypertension)
- Wildlife disruption: Migration disruption in whales (sonar), nesting disruption in birds
- Standard: Industrial noise limit 75 dB, residential 55 dB (day)
Worked Examples
Example 1 — Biomagnification (model answer)
Non-degradable toxins (e.g. DDT, mercury) enter a food chain and become more concentrated at each higher trophic level — this is biomagnification. Top predators (fish-eating birds) accumulate the highest levels, harming reproduction (e.g. thin egg shells).
Example 2 — Pollutant → effect matching
CO : toxic — binds haemoglobin, reduces O₂ transport
CO₂ : greenhouse gas → global warming
SO₂, NOₓ : acid rain
CFCs : ozone depletion
Example 3 — Greenhouse effect (model answer)
Greenhouse gases (CO₂, CH₄, N₂O, CFCs) trap outgoing infrared radiation from Earth's surface, warming the atmosphere. Rising levels enhance this effect, causing global warming and climate change.
Common Mistakes
- Confusing biomagnification (increases along food chain) with bioaccumulation (accumulates in single organism).
- Saying CO2 is a toxic pollutant — it is mainly a greenhouse gas; CO (carbon monoxide) is the toxic one.
- Forgetting that DDT's main environmental harm is through biomagnification in food chains, not direct toxicity.
- Not mentioning specific diseases for pollutants — Minamata disease (mercury), itai-itai disease (cadmium).
I. Choose the Best Answer (MCQs)
1. Which gas binds haemoglobin 200 times more strongly than oxygen?
Answer
(a) CO₂ (b) SO₂ (c) CO (d) NOₓ
2. Minamata disease is caused by poisoning of:
Answer
(a) Lead (b) Cadmium (c) Methylmercury (d) Arsenic
3. The progressive increase in concentration of a toxic substance at successive trophic levels is called:
Answer
(a) Eutrophication (b) Bioaccumulation (c) Biomagnification (d) Biodegradation
4. Which of the following is a greenhouse gas?
Answer
(a) O₂ (b) N₂ (c) CH₄ (d) CO
5. Acid rain has a pH below:
Answer
(a) 7.0 (b) 6.5 (c) 6.0 (d) 5.6
6. Itai-itai disease is caused by:
Answer
(a) Mercury (b) Lead (c) Cadmium (d) Arsenic
7. Which radioactive isotope accumulates in bones and has a long half-life?
Answer
(a) Iodine-131 (b) Caesium-137 (c) Strontium-90 (d) Cobalt-60
8. E-waste contains all of the following toxic substances EXCEPT:
Answer
(a) Lead (b) Mercury (c) Cadmium (d) Nitrogen
9. The safe noise level for residential areas during the day is:
Answer
(a) 35 dB (b) 55 dB (c) 75 dB (d) 90 dB
10. BOD is a measure of:
Answer
(a) Heavy metal pollution (b) Air quality (c) Organic pollution in water (d) Noise level
11. Which of the following causes eggshell thinning in birds?
Answer
(a) PCBs (b) Mercury (c) DDT (d) Lead
12. The 3R principle of waste management stands for:
Answer
(a) Reduce, Reuse, Recycle (b) Reduce, Recover, Recycle (c) Reuse, Recover, Reduce (d) Recover, Recycle, Reuse
II. Fill in the Blanks
1. Carbon monoxide forms carboxyhaemoglobin with haemoglobin, reducing oxygen transport. 2. The disease caused by methylmercury poisoning is called Minamata disease. 3. DDT concentration increases along the food chain through biomagnification. 4. Acid rain is caused by SO₂ and NOₓ reacting with atmospheric water vapour. 5. The greenhouse gas released by cattle during digestion is methane (CH₄). 6. The long-lived radioactive isotope Strontium-90 accumulates in bone tissue. 7. The noise level above which chronic hearing loss can occur is 80 dB. 8. Eutrophication is caused by excessive nutrient (nitrogen and phosphorus) enrichment of water bodies. 9. Itai-itai disease is caused by cadmium poisoning. 10. BOD stands for Biochemical Oxygen Demand.
III. True or False (with corrections for false statements)
1.
AnswerTrue — Carbon monoxide has 200 times greater affinity for haemoglobin than oxygen.
2.
AnswerFalse — CO₂ is the most toxic air pollutant. → Correction: CO₂ is primarily a greenhouse gas; CO (carbon monoxide) is the toxic air pollutant that harms humans directly.
3.
AnswerTrue — DDT causes eggshell thinning in raptors through biomagnification.
4.
AnswerFalse — Bioaccumulation and biomagnification are the same process. → Correction: Bioaccumulation occurs within a single organism over time; biomagnification is the increase in concentration across successive trophic levels in a food chain.
5.
AnswerTrue — Thermal pollution reduces dissolved oxygen in water, harming aquatic life.
6.
AnswerFalse — Ozone in the troposphere protects us from UV radiation. → Correction: Ozone in the stratosphere (ozone layer) protects us from UV radiation; tropospheric (ground-level) ozone is a pollutant component of photochemical smog.
7.
AnswerTrue — E-waste contains lead, cadmium, mercury, and brominated flame retardants.
8.
AnswerFalse — BOD is a measure of heavy metal pollution in water. → Correction: BOD (Biochemical Oxygen Demand) measures the amount of oxygen required by microorganisms to decompose organic matter; it indicates organic pollution, not heavy metal pollution.
IV. Match the Following
| Column A | Column B |
|---|
| 1. Mercury | c. Minamata disease |
| 2. SO₂ | f. Acid rain |
| 3. DDT | h. Eggshell thinning |
| 4. Cadmium | b. Itai-itai disease |
| 5. CO | a. Carboxyhaemoglobin |
| 6. CFCs | e. Ozone depletion |
| 7. Thermal pollution | g. Reduced dissolved oxygen |
| 8. E-waste | d. Lead, mercury, cadmium |
Answer1–c, 2–f, 3–h, 4–b, 5–a, 6–e, 7–g, 8–d
V. Answer Briefly (2-mark questions)
Q1. Differentiate bioaccumulation from biomagnification.
Answer
Bioaccumulation refers to the gradual build-up of a substance within a single organism over its lifetime, through ingestion, inhalation, or skin absorption. Biomagnification refers to the progressive increase in concentration of a substance at each successive trophic level of a food chain. While bioaccumulation is an individual-level process, biomagnification operates at the ecosystem level — top predators receive concentrated doses because they consume many contaminated prey organisms.
Q2. What is Minamata disease? Name the causative pollutant.
Answer
Minamata disease is a severe neurological syndrome first identified in Minamata Bay, Japan, in 1956. It is caused by methylmercury poisoning from industrial wastewater discharged into the bay. Symptoms include ataxia, numbness in limbs, muscle weakness, narrowing of vision, and in severe cases, paralysis and death. Methylmercury bioaccumulates in fish and shellfish, which were consumed by the local population.
Q3. State any four effects of noise pollution on humans and wildlife.
Answer
1. Hearing loss — chronic exposure above 80 dB causes permanent damage to hair cells in the cochlea. 2. Hypertension and cardiovascular stress — elevated cortisol levels and increased blood pressure. 3. Sleep disturbance — noise above 40 dB disrupts sleep patterns and causes fatigue. 4. Wildlife disruption — whale migration is disrupted by naval sonar; bird nesting and communication are affected by urban noise.
Q4. Why does thermal pollution harm aquatic organisms?
Answer
Thermal pollution raises water temperature, which reduces the solubility of dissolved oxygen. Warmer water holds less oxygen, creating hypoxic conditions. Increased temperature also accelerates metabolic rates of aquatic organisms, increasing their oxygen demand while oxygen availability decreases. This double stress leads to fish kills and disrupts breeding cycles, especially for temperature-sensitive species like trout and salmon.
Q5. List any four methods of solid waste management.
Answer
1. Landfill — engineered burial of waste in lined pits with leachate collection systems. 2. Incineration — high-temperature burning that reduces waste volume and can recover energy. 3. Composting — biological decomposition of organic waste into nutrient-rich manure. 4. Recycling — reprocessing waste materials (paper, plastic, glass, metal) into new products.
Q6. What is the greenhouse effect? Name two greenhouse gases.
Answer
The greenhouse effect is the process by which certain gases in the atmosphere trap outgoing infrared radiation from Earth's surface, causing warming of the lower atmosphere. Without it, Earth would be about 33°C colder. Two key greenhouse gases are carbon dioxide (CO₂) and methane (CH₄). Enhanced greenhouse effect from rising gas concentrations leads to global warming and climate change.
VI. Answer in Detail (5-mark questions)
Q1. Explain biomagnification with a suitable example. Why is it a serious environmental concern?
Answer
Definition: Biomagnification is the progressive increase in concentration of a persistent, fat-soluble substance at each successive trophic level of a food chain.
Mechanism:
- Persistent organic pollutants (DDT, PCBs, methylmercury) are not metabolised or excreted efficiently.
- They dissolve in lipid (fat) tissues and accumulate.
- At each trophic level, a consumer eats many prey individuals, each containing the pollutant → concentration multiplies.
DDT example:
- Water: 0.003 ppb → Zooplankton: 0.04 ppb → Small fish: 0.5 ppb → Large fish: 2 ppm → Fish-eating bird: 25 ppm
- Total magnification: roughly 10,000-fold from water to top predator.
Environmental concern:
- Eggshell thinning in raptors (bald eagle, osprey, peregrine falcon) → reproductive failure → population decline.
- Neurological damage in top mammalian predators.
- Human health risk — communities consuming contaminated fish (Minamata disease).
- Very difficult to reverse — persistent pollutants remain for decades.
Q2. Describe the effects of radioactive pollution on living organisms. Give examples of nuclear disasters.
Answer
Sources: Nuclear power plants, weapon testing, X-ray equipment, radioactive mining and ore processing.
Effects on living organisms:
- DNA damage — ionising radiation causes single- and double-strand breaks in DNA → mutations and cancer.
- Somatic effects — skin burns, cataracts, radiation sickness (nausea, vomiting, bone marrow suppression).
- Genetic effects — germline mutations passed to offspring; increased risk of leukaemia and thyroid cancer.
- Bone marrow suppression — reduced red and white blood cell production → anaemia, immune deficiency.
- Foetal abnormalities — pregnant women exposed face higher risk of congenital malformations.
- Long-lived isotopes — Cs-137 (half-life 30 yr) accumulates in muscle; Sr-90 (half-life 29 yr) accumulates in bone, both remaining hazardous for decades.
Nuclear disasters:
- Chernobyl (1986) — Reactor explosion in Ukraine; widespread fallout; thousands of thyroid cancer cases; large exclusion zone still in effect.
- Fukushima (2011) — Tsunami-damaged reactors in Japan; radioactive release into Pacific Ocean; long-term ecological monitoring ongoing.
Q3. Explain e-waste — its composition, hazards, and management strategies.
Answer
Composition of e-waste: Discarded computers, mobile phones, televisions, circuit boards, batteries. Contains toxic materials:
- Lead — from solder and CRT glass → neurotoxin, especially harmful to children.
- Mercury — from switches and LCD screens → neurological damage.
- Cadmium — from batteries and semiconductors → kidney damage, itai-itai disease.
- Chromium (VI) — from steel frames → carcinogen.
- Brominated flame retardants — from plastic casings → endocrine disruptor.
Hazards:
- Informal recycling in developing countries involves open burning and acid baths — workers (including children) are directly exposed.
- Leaching of toxins into soil and groundwater contaminates drinking water.
- Long persistence in the environment; heavy metals do not degrade.
Management strategies:
- Extended Producer Responsibility (EPR) — manufacturers take back end-of-life products.
- Formal recycling facilities — certified e-waste processors with safe extraction methods.
- India's E-Waste Management Rules (2016) — regulate collection, storage, and disposal.
- 3R principle — Reduce consumption, Reuse functional devices, Recycle components.
- Awareness campaigns — educating consumers about proper disposal channels.
Q4. Describe the effects of water pollution on aquatic life with examples.
Answer
Oil spills:
- Coat feathers of seabirds, destroying natural waterproofing and insulation → hypothermia and drowning.
- Coat fish gills → suffocation; oil contains polycyclic aromatic hydrocarbons (PAHs) that are carcinogenic.
- Example: Deepwater Horizon (2010) — massive Gulf of Mexico spill; long-term damage to marine ecosystems.
Thermal pollution:
- Power plant cooling water discharged at higher temperatures reduces dissolved oxygen.
- Accelerates metabolic rates of fish, increasing oxygen demand while supply decreases → fish kills.
- Disrupts spawning cycles; temperature-sensitive species like salmon and trout are most affected.
Acid rain:
- SO₂ and NOₓ from power plants dissolve in atmospheric water → rain with pH below 5.6.
- Lowers pH of lakes and rivers → mobilises aluminium ions from soil → toxic to fish gills.
- Dissolves calcium carbonate shells of molluscs and crustaceans → population decline.
Eutrophication:
- Excess nitrogen and phosphorus from fertilisers and sewage → algal blooms.
- Algae die and decompose → bacteria consume dissolved oxygen → hypoxic "dead zones."
- Fish and invertebrates suffocate; only tolerant species survive → biodiversity loss.
Plastic pollution:
- Microplastics ingested by zooplankton → transferred through food chain.
- Large plastic debris entangles marine mammals, turtles, and seabirds → injury and death.
- Chemical additives in plastics (phthalates, BPA) act as endocrine disruptors in fish.
Common Mistakes to Avoid
1. ❌ Confusing biomagnification with bioaccumulation ✅ Bioaccumulation = build-up within ONE organism over time; Biomagnification = increase across trophic LEVELS in a food chain.
2. ❌ Calling CO₂ a toxic pollutant ✅ CO₂ is primarily a greenhouse gas. CO (carbon monoxide) is the toxic gas that binds haemoglobin.
3. ❌ Saying DDT harms animals through direct toxicity ✅ DDT's major environmental harm comes through biomagnification in food chains, especially eggshell thinning in top predators.
4. ❌ Forgetting to name specific diseases for pollutants ✅ Mercury → Minamata disease; Cadmium → Itai-itai disease; Lead → plumbism/saturnism.
5. ❌ Confusing stratospheric ozone (protective) with tropospheric ozone (pollutant) ✅ Stratospheric ozone layer protects from UV; ground-level (tropospheric) ozone is a component of photochemical smog and irritates lungs.
6. ❌ Writing "thermal pollution increases oxygen in water" ✅ Warmer water holds LESS dissolved oxygen — thermal pollution decreases oxygen availability.
7. ❌ Listing only sources of pollution without mentioning effects on organisms ✅ Always connect the source to the biological effect (e.g., SO₂ → acid rain → aluminium toxicity in fish gills).
8. ❌ Confusing BOD with COD ✅ BOD (Biochemical Oxygen Demand) measures oxygen used by microorganisms to decompose organic matter. COD (Chemical Oxygen Demand) measures oxygen demand from both organic and inorganic oxidation.
Exam Checklist
- [ ] Can define and differentiate biomagnification vs. bioaccumulation with examples
- [ ] Can explain DDT biomagnification in a food chain with concentration values
- [ ] Can describe Minamata disease — cause, pollutant, symptoms, location
- [ ] Know itai-itai disease — cadmium poisoning, bone effects
- [ ] Can list major air pollutants (CO, SO₂, NOₓ, lead, PM2.5) and their effects on health
- [ ] Can explain greenhouse effect — mechanism, gases involved, enhanced effect
- [ ] Can describe acid rain formation (SO₂ + NOₓ) and effects on aquatic life
- [ ] Know radioactive pollution sources, isotopes (Cs-137, Sr-90), and biological effects
- [ ] Can explain e-waste composition, hazards, and management (EPR, India rules 2016)
- [ ] Can describe effects of water pollution on aquatic life — oil spills, thermal, acid rain, eutrophication, plastics
- [ ] Know noise pollution thresholds (80 dB hearing loss, 55 dB residential, 75 dB industrial)
- [ ] Can write the 3R principle and solid waste management methods
