Environment, ecology and the seven kinds of pollution

What this heading covers

The West Bengal Primary TET treats environmental studies far more substantially than the CTET does, and this block is the proof: it names four kinds of environment, the whole of basic ecology, and seven separate kinds of pollution, each as its own heading. That last point decides how to prepare. A paper with seven pollution headings will not ask seven general questions about pollution; it will ask which pollutant causes what, which movement happened where, and which control measure belongs to which problem. So this page gives each its own sources, effects and remedies rather than one list for all.

The environment

The environment is everything that surrounds a living organism and affects it — physical, biological and social.

Biotic and abiotic

	What it is	Examples
Biotic	The living components	Producers (green plants), consumers (herbivores, carnivores, omnivores), decomposers (bacteria and fungi)
Abiotic	The non-living components	Air, water, soil, minerals, sunlight, temperature, humidity, pressure

The two are not separate systems. Abiotic conditions decide which organisms can live in a place, and the organisms in turn change the soil, the air and the water — which is the idea an "interdependence" question is testing.

The social environment

The human-made and human-organised surroundings a person grows up in: family, neighbourhood, school, peer group, religion and custom, language and culture, occupation and income, and the institutions of the state — hospitals, markets, panchayats, courts, media. For a teacher, the useful point is that a child's social environment reaches the classroom with them, and explains a great deal that would otherwise be read as ability.

Environmental geography

The earth is treated as four interacting spheres:

• Lithosphere — the solid crust: rocks, minerals and soil, and the landforms built from them — mountains, plateaus and plains.
• Hydrosphere — all the water: oceans, seas, rivers, lakes, groundwater, ice. About 97 per cent of it is salt water in the oceans, and only a small fraction is fresh and available.
• Atmosphere — the envelope of gases.
• Biosphere — the narrow zone where the other three meet and life exists.

Environment-related historical events

Asked by name, date and place, so they are tabled.

Event	When	What it was
Bishnoi sacrifice at Khejarli	1730	Villagers led by Amrita Devi gave their lives to stop khejri trees being felled in Rajasthan — the earliest such movement usually cited
Silent Spring	1962	Rachel Carson's book on the effects of pesticides, which began modern environmental concern
Ramsar Convention	1971	International agreement on the conservation of wetlands
Stockholm Conference	1972	The first UN conference on the human environment; World Environment Day, 5 June, comes from it
Wildlife (Protection) Act	1972	India's law protecting wild animals and their habitat
Chipko movement	1973	Villagers in Uttarakhand, notably Gaura Devi and the women of Reni, embraced trees to stop felling; Sunderlal Bahuguna and Chandi Prasad Bhatt are the names associated with it
Project Tiger	1973	Launched to protect the tiger and its habitat
Forest (Conservation) Act	1980	Restricted the diversion of forest land
Appiko movement	1983	The Chipko idea taken up in Karnataka
Bhopal gas tragedy	1984	Leak of methyl isocyanate from a pesticide plant; thousands died — the world's worst industrial accident
Chernobyl	1986	Nuclear reactor accident in the then USSR
Environment (Protection) Act	1986	India's umbrella environmental law, passed after Bhopal
Montreal Protocol	1987	Agreement to phase out the CFCs that damage the ozone layer
Narmada Bachao Andolan	from the 1980s	Movement led by Medha Patkar against large dams on the Narmada and for those displaced
Earth Summit, Rio de Janeiro	1992	Conventions on biodiversity and climate change; Agenda 21
Kyoto Protocol	1997	Binding targets for reducing greenhouse gases
Paris Agreement	2015	Countries' own commitments to limit the rise in global temperature

Also worth holding: the Silent Valley campaign in Kerala, which stopped a dam in an evergreen forest, and Earth Day, 22 April.

Ecology and the ecosystem

Ecology is the study of the relations between organisms and their environment. The term was coined by Ernst Haeckel in 1866.

An ecosystem is a community of living organisms together with the non-living components of their surroundings, interacting as a system. The term was coined by A. G. Tansley in 1935.

• Structure: the abiotic components, plus producers, consumers and decomposers.
• Types: natural (forest, grassland, desert, pond, lake, river, ocean) and artificial (a crop field, an aquarium, a garden); or terrestrial and aquatic, and aquatic ones divided into freshwater and marine.
• Functions: the flow of energy, the cycling of nutrients, and the regulation this produces.

Food chains, webs and trophic levels

A food chain is the sequence in which one organism is eaten by the next:

grass  ->  grasshopper  ->  frog  ->  snake  ->  eagle

Each step is a trophic level: producers first, then primary consumers (herbivores), secondary consumers, tertiary consumers. Several interlocking chains make a food web, which is a truer picture of any real habitat.

Two kinds of chain are distinguished: the grazing food chain, which begins with living plants, and the detritus food chain, which begins with dead organic matter and runs through decomposers.

The ten per cent law, stated by Lindeman: only about 10 per cent of the energy at one trophic level passes to the next; the rest is used in living and lost as heat. Two consequences the paper asks for: food chains are short, rarely more than four or five links, and there are always far more producers than top consumers.

Ecological pyramids show this — pyramids of number, of biomass and of energy. The pyramid of energy is always upright; pyramids of number and biomass can be inverted, as in a single large tree supporting many insects.

And the difference that is constantly set: energy flows in one direction and is lost at each step, while nutrients are cycled and returned by decomposers. Remove a link and the whole web shifts — if snakes are killed off, frogs multiply, insects fall and the crops and the eagle are both affected.

Atmosphere, land and water

The atmosphere is about 78 per cent nitrogen and 21 per cent oxygen, with carbon dioxide, water vapour, argon and dust making up the rest. Its layers, from the ground up:

Layer	Note
Troposphere	Where weather happens; temperature falls with height
Stratosphere	Contains the ozone layer, which absorbs ultraviolet radiation; aircraft fly here
Mesosphere	Meteors burn up here
Thermosphere (with the ionosphere)	Reflects radio waves
Exosphere	The outermost, merging into space

Land: the crust, and on it soil — formed over hundreds of years by the weathering of rock mixed with humus — in its horizons of topsoil, subsoil, weathered rock and bedrock.

Water: about 97 per cent in the oceans as salt water; of the small remainder, most is locked in ice caps and glaciers, leaving a very small fraction as accessible fresh water in rivers, lakes and the ground. The water cycle keeps it moving.

Pollution

Pollution is any undesirable change in the physical, chemical or biological character of air, water or land that harms living things. A pollutant is the substance or agent that causes it. Pollutants are biodegradable (sewage, food waste — broken down naturally) or non-biodegradable (plastics, DDT, heavy metals, glass — which persist and accumulate).

Air pollution

Sources: vehicles; industry and power stations burning coal and oil; brick kilns; burning of refuse and crop stubble; domestic fuels — firewood, dung and coal, which cause serious indoor pollution; dust from construction and mining.

Chief pollutants: carbon monoxide, sulphur dioxide, oxides of nitrogen, hydrocarbons, suspended particulate matter (PM), lead, and CFCs.

Effects: respiratory disease, asthma, bronchitis and lung cancer; irritation of eyes and throat; acid rain, damaging crops, soil, buildings and monuments — the loss of shine on the marble of the Taj Mahal is the standard example, called marble cancer; smog in cities; ozone depletion from CFCs; and global warming from the increase in carbon dioxide and other greenhouse gases.

Control: cleaner fuels such as CNG and LPG; catalytic converters and pollution checks on vehicles; public transport; filters, scrubbers and electrostatic precipitators on chimneys; tall stacks; moving industry away from housing; smokeless chulhas; and planting trees.

Water pollution

Sources: untreated sewage; industrial effluent carrying acids, alkalis and heavy metals; agricultural run-off of fertiliser and pesticide; washing, bathing and cattle at the source; idol immersion and other waste put into rivers; hot water discharged from power plants (thermal pollution).

Effects: waterborne disease — cholera, typhoid, dysentery, jaundice, diarrhoea; poisoning by heavy metals, of which mercury at Minamata and arsenic in groundwater in parts of West Bengal and Bihar are the cases usually cited; eutrophication, where fertiliser run-off feeds an explosion of algae which then decays and strips the water of oxygen, killing fish. High BOD — biochemical oxygen demand — is the sign of heavy organic pollution.

Control: treatment of sewage and effluent before release; keeping bathing and washing away from drinking sources; controlled use of fertiliser and pesticide; and river action plans.

Soil pollution

Sources: excess chemical fertilisers and pesticides; industrial and mining waste; plastics; municipal refuse and unmanaged landfill; untreated sewage sludge; acid rain.

Effects: loss of fertility and of soil organisms, including earthworms; chemicals entering crops and then people; contamination of groundwater as pollutants leach down; loss of land to cultivation.

Control: organic manure, compost and vermicompost; crop rotation and biological pest control; segregating and treating waste; banning the dumping of untreated industrial waste; afforestation and checking erosion.

Sound pollution

Sound is measured in decibels (dB), and noise is unwanted or harmful sound.

Sources: vehicles and horns, loudspeakers, crackers, generators, construction, factories, aircraft, and household appliances.

Effects: hearing loss, temporary and eventually permanent; sleeplessness; headache, irritability, anxiety; raised blood pressure; loss of concentration — which matters for a school; and harm to animals. Continued exposure above about 80 dB is taken as damaging, and around 120 dB is painful.

Control: silence zones around hospitals, schools and courts; limits on horns, loudspeakers and crackers and on the hours they may be used; silencers on vehicles and generators; sound-absorbing material in buildings; and planting trees along roads, since trees absorb sound.

Ocean pollution

Sources: oil spills from tankers, offshore drilling and washing of tanks; plastic waste, which reaches the sea from rivers and coasts; sewage and industrial discharge; agricultural run-off carried down by rivers; dumping of waste at sea; and the absorption of excess carbon dioxide from the air.

Effects: an oil slick coats the sea surface and cuts off oxygen and light, and coats the feathers of seabirds and the bodies of marine animals so that they cannot float or keep warm; plastics are swallowed by turtles, fish and birds; nutrient run-off creates dead zones where nothing can live; coral bleaching follows warming and pollution; and the sea becomes more acidic as it absorbs carbon dioxide, which weakens the shells of marine animals.

Control: international rules on discharge from ships; containment booms, skimmers, absorbents and certain bacteria used in cleaning up spills; treating waste before it reaches rivers; and cutting plastic at source.

Pesticide pollution

Pesticides — insecticides, herbicides, fungicides and rodenticides — are used to protect crops, and the problem is what they do besides.

• They are not selective: they kill pollinators such as bees, natural predators of pests, earthworms, birds and fish along with the target pest.
• Many, of which DDT is the classic, are persistent: they break down very slowly and remain in the soil and water for years.
• They travel up the food chain by bioaccumulation in a single organism and biomagnification between levels, so the concentration is highest in the top consumer. DDT thinning the eggshells of birds of prey is the case Rachel Carson made in Silent Spring, and residues have been found even in Antarctic animals far from any farm.
• Pests develop resistance, so ever more is needed.
• In people the effects run from immediate poisoning of those who spray without protection to long-term harm from residues in food and water.

Control: integrated pest management, using biological control, resistant varieties, crop rotation and chemicals only as a last resort; biopesticides such as neem; organic farming; banning the most persistent compounds; proper dosage, protective equipment, and washing produce before use.

Plastic pollution

Why it is a problem in its own right: plastic is non-biodegradable and stays for hundreds of years; it is cheap and therefore used once and thrown away; it is light and travels far on wind and water.

Effects: choked drains, which turn a normal rainfall into a flood; death of cattle and of marine animals that swallow bags; poisonous gases — including dioxins — when it is burnt; loss of soil fertility where buried; and microplastics, the fragments it breaks into, now found in soil, water, fish and salt.

Control: the four Rs — refuse, reduce, reuse, recycle; cloth and jute bags in place of plastic ones; bans on identified single-use items; segregation of waste at source; deposit and buy-back schemes; and use of shredded plastic in road surfacing where that is done.

A question of the kind the paper sets

A pesticide sprayed on a crop is later found in the highest concentration in the body of a fish-eating bird living near the field. This happens because: (A) birds are sprayed directly when the crop is treated (B) the pesticide is persistent and its concentration increases at each step of the food chain (C) birds drink more water than other animals (D) the pesticide evaporates and is breathed in by birds

(B). A persistent pesticide is not excreted or broken down quickly, so it stays in the body of each organism that takes it in. A bird at the top of the chain eats many fish, each of which has eaten many smaller organisms, and the pesticide from all of them accumulates. That increase from one trophic level to the next is biomagnification.

The insight the question is really testing is the one that makes the whole of ecology useful: the harm appears farthest from where the chemical was applied, and in the organism nobody was treating. That is also the argument against judging any pollutant by its effect at the point of release.

Mistakes that cost marks here

• Listing decomposers among the abiotic components. They are living, and therefore biotic.
• Reversing the direction of energy flow, or saying nutrients flow one way. Energy flows and is lost; nutrients cycle.
• Saying 10 per cent of the energy is lost at each step. About 10 per cent is passed on.
• Saying the pyramid of numbers is always upright. Only the pyramid of energy always is.
• Confusing ozone depletion (CFCs) with global warming (carbon dioxide and other greenhouse gases). Different causes, different effects, different agreements — Montreal for one, Kyoto and Paris for the other.
• Placing the ozone layer in the troposphere. It is in the stratosphere.
• Attributing Chipko to the wrong state or decade. Uttarakhand, 1973.
• Confusing bioaccumulation (within one organism) with biomagnification (between trophic levels).
• Saying plastics are biodegradable, or that burning them disposes of them safely.
• Giving a single general list of remedies when the question names one kind of pollution.

In one line

The environment is a set of living and non-living parts locked together by the flow of energy and the cycling of matter — and every kind of pollution on this page is the same mistake repeated: putting something into that system faster than it can be broken down or carried away.

In the classroom

This is the part of the syllabus with the most local evidence available. A survey of what the class's own households throw away in a week; a walk to the nearest pond or canal and a record of what enters it; a decibel reading taken outside the school gate at different times; a food chain built entirely from animals the children can name near their homes. A fact a child has measured is worth a page of a textbook, and it is also what the pedagogy paper means when it asks for enquiry rather than telling.