CDS Biology · Ecology and Environment
Pollution and Conservation
The air pollutants and what they do, global warming and acid rain, problems of water and waste with their remedies, and how wildlife is protected in India and listed by the IUCN.
Why this matters
Fourteen CDS questions from 2016 (II) to 2026 (II), four of them in the 2016 (II) paper. Four are about air pollution, five about water, waste and remedies, and five about conservation. The two HARD ones ask what xeriscaping is and where India's cichlid fish live.
Concept 1 of 3: Air pollution, acid rain and global warming
Burning fuel puts gases into the air. Carbon monoxide gets into the blood and blocks oxygen. Sulphur and nitrogen oxides dissolve in rain and make it acidic. Carbon dioxide and methane act like the glass of a greenhouse: they let sunlight in but trap the heat that the Earth gives back, so the planet warms.
Definition
Air pollutants (NCERT Class 9 and 12):
- Carbon monoxide (incomplete burning, vehicle exhaust) binds haemoglobin about 200 times more strongly than oxygen, forming carboxyhaemoglobin, so the blood carries less oxygen; it can suffocate and kill.
- Sulphur dioxide and nitrogen oxides (burning coal and oil) dissolve in rain to form sulphuric and nitric acids: acid rain (pH below about 5.6). It corrodes marble, as at the Taj Mahal, and harms lakes and forests.
- Greenhouse gases: carbon dioxide, methane, nitrous oxide and CFCs. More of them in the air traps more heat, causing global warming, the rise in the Earth's average surface temperature.
- Methane comes mostly from landfills (rotting waste with no air), paddy fields and cattle.
- CFCs (old refrigerants and sprays) destroy the ozone layer; fly ash comes from coal-burning power stations.
| Pollutant | Main source | Effect |
|---|---|---|
| Carbon monoxide | Vehicle exhaust, incomplete burning | Blocks haemoglobin; suffocation |
| Sulphur and nitrogen oxides | Burning coal and oil | Acid rainQ CDS 2022 (I): the main reason for acid rain is sulphur and nitrogen oxides dissolving in rain. |
| Methane | Landfills, paddy fields, cattle | Greenhouse gasQ CDS 2016 (II): the gas released mostly from urban landfills is methane. |
| Carbon dioxide | Burning fuels, cutting forests | Global warmingQ CDS 2017 (II): more greenhouse gas raises the surface temperature, so Statement II explains Statement I. |
| CFCs | Old refrigerants and aerosol sprays | Ozone layer depletion |
| Fly ash | Coal-burning power stations | Dust that harms lungs and soil |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2016 · CDS (II) 2016 — General Knowledge · Q5Easy
Example 1 · Ecology and Environment · Pollution and Conservation
Which one of the following air pollutants combines with the haemoglobin of human blood and reduces its oxygen-carrying capacity, leading to suffocation and may cause even death?
Carbon monoxide, not sulphur dioxide, blocks haemoglobin
Carbon monoxide binds haemoglobin and stops it carrying oxygen. Sulphur dioxide irritates the lungs and causes acid rain; CFCs harm the ozone layer; fly ash is dust.
Acid rain needs oxides, not dust
Acid rain forms when oxides of sulphur and nitrogen dissolve in rain. Dust, minerals and soil in rain do not make it acidic.
Concept 2 of 3: Water, waste and green remedies
Some waste rots away, broken down by bacteria and fungi: it is biodegradable. Plastics do not, so they stay for hundreds of years, break into tiny bits and get into water and food. Too much fertiliser in water is a problem of a different kind: it feeds algae, or turns into a poison for babies. The remedies are simple habits: sort waste, save water, and fight pests with their natural enemies instead of chemicals.
Definition
Problems and remedies:
- Biodegradable waste (food, paper, leaves) is broken down by microbes; non-biodegradable waste (plastics, glass, metals, DDT) is not, and stays in soil and water.
- Nitrate in drinking water (from fertilisers) causes blue baby syndrome (methaemoglobinaemia): in a baby's gut nitrate turns to nitrite, which stops haemoglobin carrying oxygen.
- Eutrophication: fertiliser and sewage nutrients make algae grow wildly (an algal bloom); when they die and rot, the water loses its oxygen and fish die.
- Remedies (mitigation): segregating waste into categories at source (green bin for wet, blue for dry), recycling, xeriscaping (landscaping with drought-tolerant plants to save water).
- Biocontrol agents replace chemical pesticides: Bacillus thuringiensis (a bacterium against caterpillars), the ladybird beetle (eats aphids), Trichoderma (a fungus against plant-disease fungi), dragonflies (eat mosquitoes). Aphids are pests, not agents.
| Problem or remedy | Fact |
|---|---|
| Blue baby syndrome | Caused by nitrate in drinking waterQ CDS 2017 (II): blue baby syndrome is caused by nitrate contamination. |
| Eutrophication | Excess nutrients, algal bloom, loss of oxygen |
| Segregating waste | A mitigation measureQ CDS 2026 (II): categorical disposal of different wastes mitigates environmental problems; biomagnification and eutrophication are the problems. |
| Xeriscaping | Landscaping that saves waterQ CDS 2017 (II), HARD: xeriscaping is landscaping to save water (xeros means dry). |
| Biocontrol agents | Bt bacterium, ladybird beetle, TrichodermaQ CDS 2026 (II): the aphid is NOT a biocontrol agent; it is the pest. |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2024 · CDS (I) 2024 — General Knowledge · Q25Easy
Example 2 · Ecology and Environment · Pollution and Conservation
The use of plastics has led to a number of environment-related problems. For this, which one of the following statements is correct?
Nitrate, not nitrite, is the contaminant
Blue baby syndrome comes from nitrate in drinking water. It is turned into nitrite inside the baby's gut, which is why nitrite appears as a tempting wrong option.
A problem is not a remedy
Biomagnification, eutrophication and nuclear waste are environmental problems. Segregating waste is a remedy.
Concept 3 of 3: Conservation and protected areas
To protect wildlife, we first need to know which species are in danger, and the IUCN keeps that list for the whole world. Then the best place to protect a species is its own home, in a national park or sanctuary. Some animals are good alarm bells: frogs and other amphibians, with their thin wet skin, are the first to suffer when the environment changes.
Definition
Conservation (NCERT Class 12, and Class 11 Indian Economic Development):
- The IUCN (International Union for Conservation of Nature) publishes the Red List of threatened species, from Least Concern through Vulnerable, Endangered and Critically Endangered to Extinct.
- In situ conservation protects species in their natural home: national parks, wildlife sanctuaries, biosphere reserves. Ex situ keeps them elsewhere: zoos, botanical gardens, seed banks.
- Amphibians are the most sensitive to environmental change: thin, wet skin that absorbs pollutants, and eggs laid in water. They are used as bio-indicators.
- The environment performs four functions: it supplies resources, assimilates waste, sustains life and provides aesthetic services.
| Place or body | Known for |
|---|---|
| IUCN | Red List of threatened speciesQ CDS 2024 (I): the worldwide list of endangered species is published by the IUCN. |
| Little Rann of Kutch, Gujarat | Indian Wild Ass SanctuaryQ CDS 2016 (II): Rann of Kutch is a Wild Ass Sanctuary; Guindy is not a tiger reserve and Jaldapara is not a biosphere reserve. |
| Gir, Gujarat | Asiatic lion |
| Kaziranga, Assam | One-horned rhinoceros |
| Jaldapara, West Bengal | National park; one-horned rhinoceros |
| Namdapha, Arunachal Pradesh | Tiger reserve in rain forest |
| Guindy, Chennai | Blackbuck in a small city park |
| Kerala backwaters | Most cichlid fish in India (pearlspot, karimeen)Q CDS 2019 (II), HARD: the largest quantity of cichlids in India is in the backwaters of Kerala. |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2024 · CDS (I) 2024 — General Knowledge · Q87Easy
Example 3 · Ecology and Environment · Pollution and Conservation
Which organisation publishes worldwide list of endangered species?
Amphibians are the most sensitive
Of amphibians, reptiles, mammals and insects, the amphibians react first to changes in water, air and temperature, because of their thin, wet skin and water-laid eggs. Reptiles have dry, scaly skin and shelled eggs.
IUCN lists, WWF campaigns
The Red List is published by the IUCN. WWF is a conservation charity, UNEP a UN environment body and UNDP a UN development body; none of them publishes the list.
Four functions of the environment
The environment supplies resources, assimilates waste, sustains life and provides aesthetic services. Any option leaving one of the listed functions out is incomplete.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (3)
Air pollution, acid rain and global warming6 rows
| Pollutant | Main source | Effect |
|---|---|---|
| Carbon monoxide | Vehicle exhaust, incomplete burning | Blocks haemoglobin; suffocation |
| Sulphur and nitrogen oxides | Burning coal and oil | Acid rainQ CDS 2022 (I): the main reason for acid rain is sulphur and nitrogen oxides dissolving in rain. |
| Methane | Landfills, paddy fields, cattle | Greenhouse gasQ CDS 2016 (II): the gas released mostly from urban landfills is methane. |
| Carbon dioxide | Burning fuels, cutting forests | Global warmingQ CDS 2017 (II): more greenhouse gas raises the surface temperature, so Statement II explains Statement I. |
| CFCs | Old refrigerants and aerosol sprays | Ozone layer depletion |
| Fly ash | Coal-burning power stations | Dust that harms lungs and soil |
Water, waste and green remedies5 rows
| Problem or remedy | Fact |
|---|---|
| Blue baby syndrome | Caused by nitrate in drinking waterQ CDS 2017 (II): blue baby syndrome is caused by nitrate contamination. |
| Eutrophication | Excess nutrients, algal bloom, loss of oxygen |
| Segregating waste | A mitigation measureQ CDS 2026 (II): categorical disposal of different wastes mitigates environmental problems; biomagnification and eutrophication are the problems. |
| Xeriscaping | Landscaping that saves waterQ CDS 2017 (II), HARD: xeriscaping is landscaping to save water (xeros means dry). |
| Biocontrol agents | Bt bacterium, ladybird beetle, TrichodermaQ CDS 2026 (II): the aphid is NOT a biocontrol agent; it is the pest. |
Conservation and protected areas8 rows
| Place or body | Known for |
|---|---|
| IUCN | Red List of threatened speciesQ CDS 2024 (I): the worldwide list of endangered species is published by the IUCN. |
| Little Rann of Kutch, Gujarat | Indian Wild Ass SanctuaryQ CDS 2016 (II): Rann of Kutch is a Wild Ass Sanctuary; Guindy is not a tiger reserve and Jaldapara is not a biosphere reserve. |
| Gir, Gujarat | Asiatic lion |
| Kaziranga, Assam | One-horned rhinoceros |
| Jaldapara, West Bengal | National park; one-horned rhinoceros |
| Namdapha, Arunachal Pradesh | Tiger reserve in rain forest |
| Guindy, Chennai | Blackbuck in a small city park |
| Kerala backwaters | Most cichlid fish in India (pearlspot, karimeen)Q CDS 2019 (II), HARD: the largest quantity of cichlids in India is in the backwaters of Kerala. |
Watch out for (7)
- Carbon monoxide, not sulphur dioxide, blocks haemoglobin→ Air pollution, acid rain and global warming
- Acid rain needs oxides, not dust→ Air pollution, acid rain and global warming
- Nitrate, not nitrite, is the contaminant→ Water, waste and green remedies
- A problem is not a remedy→ Water, waste and green remedies
- Amphibians are the most sensitive→ Conservation and protected areas
- IUCN lists, WWF campaigns→ Conservation and protected areas
- Four functions of the environment→ Conservation and protected areas
Test yourself on Ecology and Environment
10 past CDS questions from this chapter, timed at 10 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.