Our Environment
How living and non-living components interact through ecosystems, food chains and energy flow, and how human activities like ozone depletion and waste generation disturb this balance.
Environment and ecology is a high-yield Prelims zone: trophic levels, the 1%/10% energy rules, biological magnification and the ozone/Montreal Protocol regime recur almost every year. For Mains it underpins GS-III themes of conservation, pollution, environmental degradation, waste management and global environmental diplomacy. This chapter is the conceptual base for understanding biodiversity, climate negotiations and India's pollution-control framework.
Understand the chapter
What an Ecosystem Is and Its Components
An ecosystem is all the interacting organisms in an area together with the non-living constituents of their environment, maintaining a balance in nature. It has two parts: biotic components (plants, animals, microbes, humans) and abiotic components (physical factors). Ecosystems are either natural or human-made (artificial).
- Biotic = living organisms; Abiotic = temperature, rainfall, wind, soil, minerals
- Natural ecosystems: forest, pond, lake
- Artificial (human-made): garden, crop-field, aquarium
- An aquarium is a self-sustaining human-made ecosystem
Producers, Consumers and Decomposers
Organisms are grouped by how they get sustenance. Producers (autotrophs) make organic food from inorganic substances using solar energy and chlorophyll. Consumers (heterotrophs) depend directly or indirectly on producers, while decomposers break dead matter into simple inorganic substances that return to the soil for reuse by plants.
- Producers/autotrophs: all green plants + certain bacteria (photosynthesis)
- Consumers: herbivores, carnivores, omnivores, parasites
- Decomposers: bacteria and fungi - recycle nutrients into soil
- Without decomposers, natural replenishment of soil nutrients fails
Food Chains, Trophic Levels and Food Webs
A series of organisms feeding on one another forms a food chain, and each step is a trophic level. Producers occupy the first level, herbivores (primary consumers) the second, small carnivores (secondary) the third and larger carnivores (tertiary) the fourth. Since each organism is eaten by many others, straight-line chains interlink into a food web.
- Level 1 Producers - Level 2 Herbivores - Level 3 Small carnivores - Level 4 Large carnivores
- Food web = many interconnected food chains (branching, not linear)
- Greatest number of individuals is at the producer level
Energy Flow - the 1% and 10% Rules
Energy flow through an ecosystem is unidirectional - it moves from the Sun to autotrophs to consumers and never returns to the previous level, and diminishes at every step. Green plants capture only about 1% of the sunlight falling on their leaves. At each transfer only an average of 10% of energy reaches the next trophic level, so food chains rarely exceed three or four steps.
- Energy flow is one-way (unidirectional), not cyclic
- Producers fix only ~1% of incident sunlight as food energy
- 10% Law (Lindeman): ~10% of energy passes to each higher level
- Severe energy loss limits chains to 3-4 trophic levels
Biological Magnification
Pesticides and other chemicals wash into soil and water bodies, are absorbed by plants and aquatic life, and thus enter the food chain. Because they are not degradable, they accumulate progressively at each trophic level. As humans occupy the top of most food chains, the maximum concentration accumulates in human bodies - this is biological magnification.
- Source: pesticides/chemicals entering soil and water
- Concentration rises at successively higher trophic levels
- Maximum accumulation in humans (top consumer)
- Residues persist in grains, vegetables, fruits and meat; not always removable by washing
Ozone Layer and Its Depletion
Ozone (O3) is three oxygen atoms; while O2 sustains aerobic life, O3 is a deadly poison at ground level. High in the atmosphere it shields Earth from the Sun's UV radiation, which causes skin cancer. It forms when high-energy UV splits O2 into free oxygen atoms that combine with O2. From the 1980s synthetic CFCs sharply depleted ozone, prompting the 1987 UNEP agreement (Montreal Protocol) to freeze CFC production at 1986 levels.
- Formation: O2 + UV gives O + O; then O + O2 gives O3
- Good ozone (upper atmosphere/stratosphere) protects; ground-level ozone is a poison
- CFCs = ozone-depleting refrigerants and fire-extinguisher chemicals
- Montreal Protocol (1987): froze CFCs at 1986 levels; CFC-free refrigerators now mandatory worldwide
Managing the Garbage We Produce
Substances broken down by biological processes are biodegradable; those that resist such breakdown are non-biodegradable. Enzymes are specific in action, so human-made materials like plastics are not digested by bacteria or saprophytes and persist for long periods under ambient conditions. Lifestyle changes and disposable packaging have sharply increased non-biodegradable waste.
- Biodegradable: vegetable peels, paper, cloth - decomposed by microbes
- Non-biodegradable: plastics, metals - inert, persist long, may harm the ecosystem
- Enzyme specificity is why plastics resist microbial breakdown
- More disposables and packaging = more non-biodegradable waste
Key terms
- Ecosystem
- All interacting organisms in an area plus the non-living (abiotic) constituents of their environment.
- Abiotic components
- Physical factors of an ecosystem - temperature, rainfall, wind, soil and minerals.
- Producer (Autotroph)
- Organism that makes food from inorganic matter using sunlight and chlorophyll - green plants and some bacteria.
- Decomposer
- Bacteria and fungi that break complex organic dead matter into simple inorganic substances returned to soil.
- Trophic level
- A feeding step in a food chain; producers are the first trophic level.
- Food web
- A network of many interlinked food chains, since each organism is eaten by several others.
- 10% Law
- On average only 10% of energy at one trophic level is passed on to the next.
- Biological magnification
- Progressive accumulation of non-degradable chemicals at successive trophic levels, peaking in top consumers (humans).
- CFCs
- Chlorofluorocarbons - synthetic refrigerant/fire-extinguisher chemicals that deplete the ozone layer.
- Biodegradable vs Non-biodegradable
- Substances that are broken down by biological processes versus those that resist breakdown and persist.
Must-know facts exam-ready
- Ecosystem = biotic components + abiotic components
- Natural ecosystems: forest, pond, lake; Artificial: garden, crop-field, aquarium
- Producers/autotrophs occupy the first trophic level and capture about 1% of incident sunlight
- 10% Law (Lindeman's law): only ~10% of energy transfers to the next trophic level
- Food chains generally have only 3-4 trophic levels due to energy loss
- Energy flow in an ecosystem is unidirectional; greatest number of individuals is at the producer level
- Decomposers are micro-organisms - bacteria and fungi
- Biological magnification gives maximum chemical concentration in humans (top of food chain)
- Ozone is O3 (three oxygen atoms); O2 sustains life but ground-level O3 is a poison
- Ozone shields Earth from UV radiation, which causes skin cancer; ozone began dropping sharply in the 1980s
- CFCs cause ozone depletion; the 1987 UNEP agreement (Montreal Protocol) froze CFC output at 1986 levels
- Montreal Protocol was opened on 16 September - now International Ozone Day
Timeline
- 1980sAtmospheric ozone begins dropping sharply, linked to CFCs
- 1985Vienna Convention - framework treaty for protecting the ozone layer
- 1986Reference year - baseline level at which CFC production was later frozen
- 1987UNEP-brokered Montreal Protocol freezes CFC production at 1986 levels (signed 16 September)
- 2016Kigali Amendment to Montreal Protocol - phase-down of HFCs
Memory tricks remember it for good
Traps to avoid
- Good ozone (upper atmosphere, protective shield) versus bad ozone (ground level, a poison/pollutant) - UPSC swaps these.
- O3 is ozone; O2 is the oxygen we breathe - the chapter stresses O2 is essential while O3 is a deadly poison at ground level.
- Do not confuse the 1% (sunlight captured by plants) with the 10% law (energy passed up each level) - they are different numbers.
- Energy flow is unidirectional and lost at each step; only nutrients cycle, energy never returns to a previous level.
- Vienna Convention (1985) is only a framework; the Montreal Protocol (1987) is the operative CFC-freezing agreement - don't interchange them.
- Decomposers are micro-organisms (bacteria and fungi), not small animals; and some bacteria are producers, not consumers.
Exam focus
🧠 Prelims angles
- Trophic-level identification and 10% law numerical/sequence questions
- Biological magnification - which trophic level shows maximum chemical concentration
- Ozone chemistry (O3 formation), its stratospheric location and UV-skin cancer link
- Year-matching of ozone treaties: Vienna 1985, Montreal Protocol 1987, Kigali 2016, and Ozone Day (16 September)
- Classification of substances as biodegradable versus non-biodegradable
- Distinction between a food chain and a food web, and producer dominance in individual numbers
✍️ Mains angles GS-III
- The Montreal Protocol is hailed as the most successful environmental treaty - examine.Use universal ratification, measurable ozone recovery and the Kigali HFC phase-down; contrast with weaker climate regimes.
- Discuss the challenges of non-biodegradable and e-waste management in India.Link rising disposables and plastics to source segregation, recycling, circular economy and producer responsibility.
- How does biological magnification threaten food safety and public health?Trace pesticide flow into food chains, peak accumulation in humans, and the case for regulating agro-chemicals.
Last-minute revision tick as you recall
- Ecosystem = biotic + abiotic; natural (forest, pond, lake) vs artificial (garden, crop-field, aquarium)
- PCD = Producers, Consumers, Decomposers; decomposers = bacteria + fungi
- Plants trap ~1% of sunlight; only ~10% energy moves up each level (Lindeman)
- Energy flow is unidirectional; chains limited to 3-4 links; most individuals at producer level
- Biological magnification peaks in humans at the food-chain top
- Ozone = O3 in the upper atmosphere, blocks UV, prevents skin cancer
- CFCs depleted ozone from the 1980s; Montreal Protocol 1987 froze them at 1986 levels (Ozone Day 16 Sept)
- Biodegradable broken down by microbes; non-biodegradable (plastics) persist due to enzyme specificity
Distilled from NCERT Class 10 · Science (Class 10) for UPSC. Always cross-check facts with the original NCERT.