CDS Biology · Formula sheet
Ecology and Environment formulas
1 formula, 5 reference tables and 13 common traps for CDS Biology Ecology and Environment, grouped by subtopic.
Ecosystems and Energy Flow
Learn this subtopic in the notesEnergy flow and the ten per cent law
Energy at a trophic level
- energy fixed by the producers (first level)
- energy available at level n
- number of the trophic level
Population, community, ecosystem and succession
| 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 biomagnification
| 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. |
Common traps
Community has no soil or water in it
A community is only the living part. Add the abiotic part (soil, water, air, light) and it becomes an ecosystem. A population is one species only.
Succession starts with nudation
Succession cannot begin until there is a bare area: nudation comes first and stabilisation last, with migration and reaction in between in that order.
A food chain starts with a producer
Every food chain begins with a green plant and then runs through animals that eat each other. A set of only herbivores, or one that puts the grass last, is not a food chain.
Accumulation is one body, magnification is up the chain
Bioaccumulation happens within one organism. Biomagnification is the rise from one trophic level to the next. The plankton-to-fish observation is biomagnification.
Energy one way, nutrients in a cycle
Energy flows one way and is lost as heat. Nutrients cycle, returned by decomposers. Options that make energy cyclic, or both flows the same, are wrong.
Energy, not food or parasites, limits the chain
A food chain stops at 4 or 5 levels because the energy available falls tenfold at each step. Shortage of food in general, polluted air or parasites are not the reason.
Pollution and Conservation
Learn this subtopic in the notesAir pollution, acid rain and global warming
| 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 remedies
| 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 areas
| 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. |
Common traps
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.
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.
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.