CDS Biology · Free notes
Ecology and Environment: CDS Biology
Ecology and Environment has 22 past-year questions in CDS General Knowledge, from 2016 (II) to 2026 (II): 12 EASY, 7 MODERATE and 3 HARD. The 2016 (II) and 2017 (II) papers carried four each, and seven of those eight were on pollution and conservation. Most are single facts: which gas comes from landfills, which body keeps the Red List, which set of organisms makes a food chain. The ideas worth learning as rules are the ten per cent law of energy, the difference between bioaccumulation and biomagnification, and the order of the stages of succession.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Ecosystems and Energy Flow
8 PYQsPopulation, community, ecosystem and biome, how a community develops by succession, how food chains pass on food and poisons, and why energy dwindles at each step.
Pollution and Conservation
14 PYQsThe 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.
Formula & revision sheet
1 formulas · 5 reference tables · 13 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
1 formulas · 5 reference tables · 13 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (2)
Population, community, ecosystem and succession5 rows
| Level or stage | Meaning |
|---|---|
| Population | One species, same area, same timeQ CDS 2021 (II): a population is a group of organisms of one species living in the same area at the same time. |
| Community | Many species living together |
| Ecosystem | Community plus its abiotic environment |
| Biome | Large region of one climate and vegetation type |
| Succession | Nudation, migration, reaction, stabilisationQ CDS 2019 (II), HARD: the order is Nudation, Migration, Reaction and Stabilization. |
Food chains and biomagnification6 rows
| Trophic level | Role | Example |
|---|---|---|
| First | Producer | Grass, phytoplankton |
| Second | Primary consumer (herbivore) | Insect, deer, zooplankton |
| Third | Secondary consumer | Frog, small fish |
| Fourth | Tertiary consumer | Snake, big fish |
| Top | Top carnivore; gathers the most pesticide | Hawk, fish-eating birdQ CDS 2018 (I): bioaccumulation is build-up in one organism; large fish holding more pesticide than plankton is biomagnification, so Statement II does not explain Statement I. |
| All levels | Decomposers return nutrients | Bacteria, fungiQ CDS 2019 (II): a food chain is the passage of food, and so energy, from one organism to another. |
Watch out for (6)
- Community has no soil or water in it→ Population, community, ecosystem and succession
- Succession starts with nudation→ Population, community, ecosystem and succession
- A food chain starts with a producer→ Food chains and biomagnification
- Accumulation is one body, magnification is up the chain→ Food chains and biomagnification
- Energy one way, nutrients in a cycle→ Energy flow and the ten per cent law
- Energy, not food or parasites, limits the chain→ Energy flow and the ten per cent law
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
PYQ weightage by concept
6 concepts · 22 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
6 concepts · 22 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Population, community, ecosystem and succession | 3 | 14% |
| Food chains and biomagnification | 3 | 14% |
| Energy flow and the ten per cent law | 2 | 9% |
| Concept | PYQs | Share |
|---|---|---|
| Water, waste and green remedies | 5 | 23% |
| Conservation and protected areas | 5 | 23% |
| Air pollution, acid rain and global warming | 4 | 18% |
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.