BharatNotes Why this chapter matters for UPSC: "Life on the Earth" was Chapter 15 of the old Fundamentals of Physical Geography. It was dropped in NCERT's rationalisation: the current textbook (Rationalised Edition, Reprint 2026-27) has 14 chapters, and its Unit VI "Life on the Earth" now contains only Chapter 14, Biodiversity and Conservation. That chapter still says "You have studied about the ecosystem in the earlier chapter", and this page is that earlier chapter. UPSC still tests its content: ecosystems and food chains, biomes, and the carbon and nitrogen cycles appear in Prelims and in GS1 geography and GS3 environment questions.
Contemporary hook: The Global Carbon Budget 2025 (Friedlingstein et al., Earth System Science Data, 2026) puts the global mean atmospheric CO₂ concentration at 422.8 ppm for 2024 and projects 425.6 ppm for 2025, about 53% above the pre-industrial level of about 278 ppm. The carbon cycle described in this chapter is the system that number measures.
Scope note: We could not retrieve the pre-rationalised NCERT PDF of this chapter. The page covers the chapter's standard scope (biosphere, ecosystems, biomes, biogeochemical cycles) from the current NCERT books and from primary scientific and government sources, each cited below.
🧠 First Principles — Read This First
The biosphere is the part of the Earth where life exists: the soil, the lower atmosphere, and the water of rivers, lakes and oceans. It overlaps the other three spheres. Plants take carbon dioxide from the air, water from the soil and minerals from weathered rock, so life depends on all of them.
An ecosystem is a group of living things together with their non-living surroundings in one place, for example a pond, a forest patch or a grassland. Inside an ecosystem, green plants capture sunlight and make food. Animals that eat plants get part of that energy, and animals that eat those animals get a smaller part. At each step most of the energy is used up and lost as heat. Energy therefore flows one way through an ecosystem and must be supplied continuously by the Sun.
Matter behaves differently. The carbon, nitrogen and water in a leaf are taken from the environment and returned to it when the leaf decays, through bacteria and fungi called decomposers. The same atoms are used again. These loops are called biogeochemical cycles.
A biome is a very large region with a typical type of vegetation, such as tropical rainforest, desert or tundra, together with the animals adapted to it. Climate decides which plants can grow, and the plants decide which animals can live there, so the world map of biomes closely follows the world map of climates. If you know the climate of a place, you can predict its natural vegetation.
Why UPSC cares: food chains, the 10% rule and biomagnification are Prelims staples, and the carbon and nitrogen cycles connect this chapter to climate change and water pollution in GS3.
PART 1 — Quick Reference
Table 1: Major world biomes
| Biome | Climate | Vegetation | Typical animals | Main locations |
|---|---|---|---|---|
| Tropical rainforest | Hot and wet throughout the year | Tall, multi-layered evergreen forest; epiphytes and climbers | Jaguars, toucans, primates; very high species richness | Amazon, Congo basin, South-East Asia; in India the Western Ghats, NE hills, A&N Islands |
| Tropical savanna | Warm; a long dry season | Grassland with scattered drought-resistant trees; fire common | Large grazing herds and their predators | Sub-Saharan Africa, northern Australia, parts of South America |
| Tropical deciduous (monsoon) forest | Warm; seasonal rainfall | Trees shed leaves in the dry season | Deer, monkeys, big cats | India (NCERT's "most widespread forests in India"), South-East Asia |
| Hot desert | Very low rainfall; large daily temperature range | Sparse xerophytes and succulents | Camels, reptiles, burrowing rodents | Sahara, Arabia, Thar, Atacama |
| Mediterranean shrubland | Hot dry summers, mild wet winters | Hard-leaved, fire-adapted shrubs (maquis, chaparral) | Small mammals, many birds | Mediterranean basin, California, south-west Australia, Cape region |
| Temperate grassland | Moderate to low rainfall; cold winters | Grasses with few trees | Grazers such as bison; burrowing animals | Prairies, Pampas, Steppes |
| Temperate deciduous forest | Moderate rainfall; cold winters | Broad-leaved trees that shed leaves in winter (oak, maple, beech) | Deer, foxes, bears | Eastern North America, Europe, eastern China |
| Boreal forest (taiga) | Short cool summers; long, very cold winters | Conifers (pine, spruce, fir, larch) | Moose, wolves, lynx | Canada, Scandinavia, Siberia |
| Tundra | Very short growing season; permanently frozen subsoil (permafrost) | Mosses, lichens, dwarf shrubs; no trees | Caribou, musk ox, Arctic fox, lemmings | Arctic coasts of North America and Eurasia; high mountains (alpine tundra) |
| Aquatic (freshwater and marine) | Set by water temperature, depth, light and salinity | Phytoplankton, algae, aquatic plants, mangroves, seagrass | Fish, amphibians, marine mammals | Rivers, lakes, wetlands, estuaries, oceans |
Source: standard biome classification; Indian locations from NCERT India: Physical Environment Ch 5 (Reprint 2026-27).
Table 2: The four biodiversity hotspots that include Indian territory
| Hotspot | Indian part | Other countries | Note |
|---|---|---|---|
| Western Ghats and Sri Lanka | Western Ghats | Sri Lanka | Source of many peninsular rivers |
| Himalaya | North-western and north-eastern Himalayan states | Pakistan, Nepal, Bhutan, south-west China; the eastern end adjoins Myanmar | Separated from Indo-Burma in a 2004 reappraisal |
| Indo-Burma | Parts of north-east India (PIB calls it "the Northeast region") | Myanmar, Thailand, Cambodia, Laos, Vietnam, southern China | Over 300 million people live in it, more than in any other hotspot (CEPF) |
| Sundaland | Nicobar Islands | Southern Thailand, Malaysia, Singapore, Brunei, western Indonesia | About 25,000 vascular plant species, 60% endemic (CEPF) |
Source: Critical Ecosystem Partnership Fund (CEPF) hotspot pages, accessed 1 Oct 2026; PIB backgrounder "India's Wildlife Conservation Milestones", 3 Mar 2025.
A hotspot must have at least 1,500 endemic vascular plant species and must have lost at least 70% of its primary native vegetation. Norman Myers named the first 10 hotspots in 1988; the two numerical thresholds were introduced in Conservation International's 1999 global review. There are 36 hotspots (CEPF, count unchanged since the North American Coastal Plain was added in February 2016). PIB's March 2025 backgrounder still says "34", the count from 2005.
Table 3: The global carbon cycle in numbers (Global Carbon Budget 2025)
| Flux or stock | Value | Year |
|---|---|---|
| Fossil CO₂ emissions | 10.3 ± 0.5 GtC per year | 2024 |
| Land-use change emissions (mainly deforestation) | 1.3 ± 0.7 GtC per year | 2024 |
| Total human CO₂ emissions | 11.6 ± 0.9 GtC per year (42.4 GtCO₂) | 2024 |
| Ocean sink (net uptake) | 3.4 ± 0.4 GtC per year | 2024 |
| Land sink (net uptake by vegetation) | 1.9 ± 1.1 GtC per year | 2024 |
| Atmospheric growth | 7.9 ± 0.2 GtC per year (3.73 ppm per year) | 2024 |
| Global mean atmospheric CO₂ | 422.8 ppm; projected 425.6 ppm for 2025 | 2024 / 2025 (preliminary) |
Source: Friedlingstein et al., "Global Carbon Budget 2025", Earth System Science Data 18, 3211–3288 (2026), abstract. Derived arithmetic, not a published figure: at the standard conversion of about 2.12 GtC per ppm, 422.8 ppm corresponds to roughly 900 GtC in the atmosphere, and the ocean took up about 29% of human emissions in 2024 (3.4 ÷ 11.6).
Table 4: The nitrogen cycle
| Stage | What happens | Agents |
|---|---|---|
| Fixation | N₂ from the air → ammonia/ammonium | Rhizobium in legume root nodules; free-living Azotobacter; cyanobacteria; lightning; the industrial Haber process |
| Nitrification | Ammonium → nitrite → nitrate | Nitrosomonas, Nitrobacter |
| Assimilation | Plants absorb nitrate and ammonium to build proteins | Plants |
| Ammonification | Dead organic matter → ammonium | Decomposer bacteria and fungi |
| Denitrification | Nitrate → N₂ (and some N₂O) back to the air | Denitrifying bacteria (e.g. Pseudomonas), in low-oxygen soils and water |
Table 5: India's natural vegetation (NCERT India: Physical Environment Ch 5)
| Type | Rainfall (NCERT) | Where | Typical species (NCERT) |
|---|---|---|---|
| Tropical evergreen and semi-evergreen | Over 200 cm; mean annual temperature above 22°C | Western slopes of the Western Ghats, hills of the north-east, A&N Islands | Evergreen: rosewood, mahogany, aini, ebony. Semi-evergreen: white cedar, hollock, kail |
| Moist deciduous | 100–200 cm | NE states along the Himalayan foothills, eastern slopes of the Western Ghats, Odisha | Teak, sal, shisham, hurra, mahua, amla, semul, kusum, sandalwood |
| Dry deciduous | 70–100 cm | Rainier parts of the Peninsula; plains of UP and Bihar | Tendu, palas, amaltas, bel, khair, axlewood |
| Tropical thorn | Less than 50 cm | Semi-arid SW Punjab, Haryana, Rajasthan, Gujarat, MP, UP | Babool, ber, wild date palm, khair, neem, khejri, palas |
| Montane (Himalaya) | Changes with altitude | Wet temperate forest at 1,000–2,000 m (oak, chestnut); chir pine at 1,500–1,750 m; blue pine and spruce at 2,225–3,048 m; silver fir, juniper, birch, rhododendron at 3,000–4,000 m; then alpine pastures, mosses and lichens | Deodar in the western Himalaya |
| Montane (south) | — | Nilgiri, Anaimalai and Palani hills (sholas) | Magnolia, laurel, cinchona, wattle |
| Littoral and swamp (mangroves) | Tidal, saline | A&N Islands, Sunderbans; also Mahanadi, Godavari and Krishna deltas | Salt-tolerant species; NCERT gives 4,992 sq km, 7% of world mangroves (undated textbook figure) |
Source: NCERT, India: Physical Environment, Ch 5 "Natural Vegetation", Reprint 2026-27.
PART 2 — Concepts & Narrative
The biosphere and the ecosystem
The biosphere is the zone where the lithosphere, hydrosphere and atmosphere meet and support life. Most living matter is concentrated near the surface: in the soil, the lowest layer of the atmosphere and the sunlit upper layer of water bodies. The lithosphere supplies mineral nutrients from weathered rock, the hydrosphere supplies water, and the atmosphere supplies carbon dioxide for photosynthesis and oxygen for respiration.
An ecosystem has two kinds of components. The abiotic (non-living) components are sunlight, temperature, water, air, soil and minerals. The biotic (living) components fall into three groups:
- Producers (autotrophs): green plants, algae and some bacteria that make food from sunlight by photosynthesis.
- Consumers (heterotrophs): herbivores (primary consumers), carnivores that eat herbivores (secondary consumers), and higher carnivores.
- Decomposers: bacteria and fungi that break down dead matter and return nutrients to the soil and water.
Ecosystems are commonly divided into terrestrial (forests, grasslands, deserts) and aquatic (freshwater and marine). Their boundaries are not sharp, as the current NCERT Ch 14 notes, so drawing an ecosystem's edge is often a matter of judgement.
Food chain, food web and the 10% rule. A food chain is a single line of feeding: grass → deer → tiger. Each step is a trophic level. Real ecosystems have many interlinked chains, called a food web. As a rough rule, only about a tenth of the energy at one trophic level is passed on to the next; the rest is used in respiration and lost as heat. This is why food chains rarely have more than four or five links and why top predators are always few. Drawn as a diagram, the numbers or biomass at each level usually form an ecological pyramid with producers at the base.
Energy flows; nutrients cycle. Energy enters an ecosystem as sunlight, is fixed by producers and passes up the trophic levels, shrinking at each step until it is all lost as heat. It cannot be reused. Nutrients such as carbon, nitrogen and phosphorus are different: decomposers return them from dead organisms to the soil, water and air, and producers take them up again. An ecosystem therefore needs a continuous input of solar energy but recycles a fixed stock of matter. Two consequences follow. Without decomposers, nutrients would stay locked in dead matter and production would stop. And a substance that organisms absorb but cannot break down or excrete, such as some organochlorine pesticides, becomes more concentrated at each higher trophic level. This is biomagnification, and it explains why the top predator in a sprayed food chain carries the highest load (UPSC asked exactly this in Prelims 2010; see Practice Questions).
Biomes follow climate
A biome is identified by its dominant plant form, such as tall evergreen trees, grasses or mosses, and this is set mainly by temperature and moisture. Because climate changes broadly with latitude, biomes form rough belts from the equator to the poles: rainforest in the wet equatorial zone; savanna and monsoon forest where a dry season appears; hot deserts under the dry subtropical high-pressure belts, especially on the western sides of continents; Mediterranean shrubland, temperate grassland and temperate forest in the mid-latitudes; boreal forest further poleward; and tundra and ice near the poles. The site's Chapter 12 (World Climate) describes the Köppen climate types that this sequence follows.
Altitude repeats the pattern on a smaller scale. Temperature falls with height, so climbing a high tropical mountain passes through vegetation zones similar to those met when travelling towards the poles. NCERT describes this for the Himalaya: "a succession of vegetation from the tropical to the tundra" (Table 5).
Continents also differ along the same latitude. The western sides of continents near 20°–30° are dry because cold ocean currents and subsiding air suppress rain, while eastern sides at the same latitudes receive moist onshore winds. UPSC asked why the major hot deserts lie in this position in Mains 2013 (gs1-pyq-2013-21).
Tropical rainforest
Tropical rainforests grow where it is warm and wet throughout the year. The current NCERT Ch 14 states that tropical rainforests "contain 50 per cent of the species on the earth". The forest is layered: NCERT's India volume describes evergreen forests with shrubs and creepers near the ground, shorter trees above them and tall trees reaching "up to 60 m or above", with no fixed season for leaf fall, so the forest stays green all year.
Rainforest soils are usually poor. Warmth and moisture make decomposition fast, and most nutrients are held in the living plants rather than in the soil. When the forest is cleared, heavy rain washes out the remaining nutrients, so cleared land often loses its fertility within a few years.
India's rainforests lie on the western slopes of the Western Ghats, in the hills of the north-east and in the Andaman and Nicobar Islands (NCERT). They fall in three different hotspots: the Western Ghats in the Western Ghats–Sri Lanka hotspot, the north-eastern forests in the Indo-Burma and Himalaya hotspots, and the Nicobar Islands in Sundaland (Table 2).
Savanna and monsoon forest
Where a long dry season interrupts the rains, closed forest gives way to tropical deciduous forest or to savanna. In savannas, grasses dominate and trees are scattered. Periodic fire and grazing keep trees from closing the canopy, and many savanna plants survive fire. In India the equivalent is the tropical deciduous (monsoon) forest, which NCERT calls "the most widespread forests in India", found where rainfall is 70–200 cm. Its trees shed their leaves in the dry season.
Taiga, tundra and permafrost
The boreal forest or taiga is a belt of conifers across northern North America and Eurasia. The tundra lies poleward of it and is treeless: the growing season is very short and the subsoil is permafrost, ground that stays frozen for at least two consecutive years. Permafrost prevents drainage and deep rooting.
A common error is to say that the taiga has no permafrost. Large parts of it do. In eastern Siberia the larch-dominated taiga coincides closely with the zones of continuous and discontinuous permafrost. Zhang, Yasunari and Ohta (Environmental Research Letters, 2011) describe the two as a coupled system: the trees intercept sunlight and limit summer thawing, and the frozen layer below holds water in the thawed surface layer, which the larches depend on. Their model suggests the coupling breaks down under warming of about 2°C or more. The difference between taiga and tundra is the presence of trees, not the presence of permafrost.
High-latitude ecosystems are warming fast. Rantanen et al. (Communications Earth & Environment, August 2022) found that the Arctic warmed nearly four times faster than the global average over 1979–2021. Permafrost soils store large amounts of organic carbon; as they thaw, microbes release it as carbon dioxide and methane, which adds to warming.
Alpine tundra occurs above the treeline on high mountains. In India it appears as the alpine pastures and the moss-and-lichen zone of the Himalaya above the 3,000–4,000 m forest belt (NCERT), used for seasonal grazing by groups such as the Gujjars, Bakarwals, Bhotiyas and Gaddis.
The carbon and nitrogen cycles and GS3
Carbon cycle. Photosynthesis removes CO₂ from the air; respiration, decomposition and fires return it. The oceans exchange CO₂ with the air, and over geological time buried organic matter became coal, oil and gas. Burning fossil fuels and clearing forests add carbon to the air faster than the ocean and land sinks remove it. In 2024 humans emitted 11.6 GtC, the ocean and land sinks took up about 5.3 GtC, and the atmosphere gained 7.9 GtC (Table 3; the budget did not close exactly in 2024, as its authors note). The Global Carbon Budget 2025 also reports that climate change and deforestation have turned South-East Asian and large parts of South American tropical forests from CO₂ sinks into CO₂ sources.
Nitrogen cycle. Air is about 78% nitrogen, but plants cannot use N₂ directly; it must first be fixed (Table 4). Synthetic fertiliser made by the Haber process has greatly raised crop yields. Nitrogen and phosphorus that wash off fields into rivers and the sea cause eutrophication: algae multiply, die and decompose, and the decomposition uses up dissolved oxygen. The IPBES Global Assessment (May 2019) counted more than 400 fertiliser-driven coastal "dead zones" covering over 245,000 km². UPSC asked about the consequences of dead zones in Mains 2018 (gs1-pyq-2018-07). Nitrous oxide (N₂O) released from fertilised soils is also a greenhouse gas.
Water cycle. Covered in Chapter 11 (Water in the Atmosphere). Forests return water to the air by transpiration and regulate river flow.
India's biodiversity in the global picture
India is one of 17 megadiverse countries identified by UNEP's World Conservation Monitoring Centre. The current NCERT Ch 14 uses an older list of 12 "mega diversity centres" (Mexico, Colombia, Ecuador, Peru, Brazil, DR Congo, Madagascar, China, India, Malaysia, Indonesia, Australia). Answer NCERT-based questions with 12 and current-affairs questions with 17.
The government's figures (PIB backgrounder, 3 Mar 2025) are that India covers 2.4% of the world's land and holds 7–8% of known species, including over 45,000 plant and 91,000 animal species. NCERT's India: Physical Environment Ch 5 gives an older estimate of "4-5 per cent of all known plant and animal species". India includes parts of four hotspots (Table 2). Threats and the conservation response are covered in the next chapter (Biodiversity and Conservation).
PART 3 — UPSC Integration
Cross-paper relevance
- GS1 (Geography): distribution of natural vegetation and biomes; why deserts and rainforests lie where they do (gs1-pyq-2013-21, gs1-pyq-2023-17).
- GS3 (Environment): decomposition and the carbon cycle (gs3-pyq-2022-09), carrying capacity of ecosystems (gs3-pyq-2019-18), nutrient pollution and dead zones (gs1-pyq-2018-07), carbon sinks and climate change.
Biogeochemical cycles: key linkages
| Cycle | Gas phase | Key processes | Main human disturbance |
|---|---|---|---|
| Carbon | CO₂, CH₄ | Photosynthesis, respiration, decomposition, ocean exchange | Fossil-fuel burning, deforestation |
| Nitrogen | N₂, N₂O | Fixation, nitrification, denitrification | Synthetic fertiliser, combustion |
| Water | Water vapour | Evaporation, transpiration, precipitation | Deforestation, groundwater extraction |
| Phosphorus | None | Rock weathering, uptake, decomposition, sedimentation | Fertiliser and sewage run-off (eutrophication) |
PYQ pattern (from the question banks)
- Prelims: biomagnification along a food chain (Prelims 2010, bank ID env-055); India's biodiversity hotspots (Prelims 2010, env-054); mangrove ecosystems (prelims-2026-gs1-033).
- Mains: decomposition of cellulose to CO₂ and water (GS3 2022, gs3-pyq-2022-09); carrying capacity of an ecosystem (GS3 2019, gs3-pyq-2019-18); diversity of natural vegetation in India and sanctuaries in rain forest regions (GS1 2023, gs1-pyq-2023-17); dead zones and marine ecosystems (GS1 2018, gs1-pyq-2018-07); location of hot deserts (GS1 2013, gs1-pyq-2013-21).
Mains frameworks
- Ecosystem functioning: producers → consumers → decomposers; energy flow vs nutrient cycling; why removing decomposers or top predators destabilises the system.
- Carbon cycle and climate: sources (fossil fuels, land-use change) vs sinks (ocean, land); evidence that sinks are weakening; role of forests and soils.
- Nutrient pollution: fertiliser and sewage → eutrophication → hypoxia and dead zones → fisheries loss; remedies such as balanced fertiliser use and wastewater treatment.
Exam Strategy
- Taiga vs tundra: both can lie on permafrost. Tundra is treeless; taiga is coniferous forest. Do not accept "taiga has no permafrost".
- Rainforest soils are poor even though the vegetation is the richest; nutrients sit in the biomass.
- Biomagnification vs bioaccumulation: bioaccumulation is build-up within one organism over its life; biomagnification is the increase from one trophic level to the next. The top predator has the highest concentration.
- Nitrogen fixation is done by bacteria (symbiotic Rhizobium in legumes, free-living Azotobacter, cyanobacteria) and by lightning and the Haber process, not by the plant itself.
- Megadiverse count: NCERT says 12; UNEP-WCMC says 17.
- Hotspot count: 36 (CEPF, since 2016); some government documents still print 34. The criteria are ≥1,500 endemic vascular plants and ≥70% loss of primary native vegetation.
- Nicobar ≠ Andaman in hotspot terms: the Nicobar Islands are in Sundaland.
- NCERT thresholds for Indian forests: evergreen over 200 cm; deciduous 70–200 cm (moist 100–200, dry 70–100); thorn under 50 cm.
Practice Questions
- UPSC Prelims 2010 (bank ID env-055): "A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop. The food chain is: Food crop → Rat → Snake → Hawk. In this food chain, the highest concentration of the pesticide would accumulate in which one of the following?" (a) Food crop (b) Rat (c) Snake (d) Hawk. Answer: (d), biomagnification.
- UPSC Prelims 2010 (bank ID env-054): "Consider the following statements: 1. Biodiversity hotspots are located only in tropical regions. 2. India has four biodiversity hotspots i.e., Eastern Himalayas, Western Himalayas, Western Ghats, and Andaman & Nicobar Islands. Which of the statements given above is/are correct?" (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2. Official key: (b). Note that the hotspot names in statement 2 are loose; see Table 2 for the correct four.
- UPSC Mains GS3 2022 (gs3-pyq-2022-09): "Each year a large amount of plant material, cellulose, is deposited on the surface of Planet Earth. What are the natural processes this cellulose undergoes before yielding carbon dioxide, water and other end products?"
- UPSC Mains GS3 2019 (gs3-pyq-2019-18): "Define the concept of carrying capacity of an ecosystem and discuss its relevance to sustainable regional development."
- Practice (UPSC-pattern, not a past paper): Consider the following statements: 1. Permafrost occurs only in the tundra biome. 2. Much of the larch forest of eastern Siberia grows on permafrost. 3. Tropical rainforest soils are generally rich in nutrients. Which of the statements given above is/are correct? Answer: 2 only.
📦 Revision Capsule
Hard Facts
- "Life on the Earth" (old Ch 15) was dropped in rationalisation; current FoPG Unit VI has only Ch 14, Biodiversity and Conservation (Reprint 2026-27)
- Ecosystem = biotic (producers, consumers, decomposers) + abiotic components
- About a tenth of energy passes to the next trophic level (10% rule); energy flows one way, nutrients cycle
- Global mean CO₂: 422.8 ppm (2024); 425.6 ppm projected for 2025, about 53% above the ~278 ppm pre-industrial level (Global Carbon Budget 2025)
- Human CO₂ emissions 11.6 GtC in 2024: fossil 10.3, land-use change 1.3; ocean sink 3.4, land sink 1.9 GtC (GCB 2025)
- Nitrogen fixation by Rhizobium, Azotobacter, cyanobacteria, lightning and the Haber process; denitrification returns N₂ to the air
- Over 400 fertiliser-driven coastal dead zones, over 245,000 km² (IPBES, May 2019)
- Taiga can lie on permafrost (eastern Siberian larch taiga coincides with continuous and discontinuous permafrost); tundra is treeless
- Arctic warmed nearly four times faster than the globe, 1979–2021 (Rantanen et al., 2022)
- Hotspot criteria: ≥1,500 endemic vascular plants and ≥70% loss of primary vegetation; 36 hotspots (CEPF); India in four (Western Ghats–Sri Lanka, Himalaya, Indo-Burma, Sundaland via the Nicobars)
- Megadiverse countries: 17 (UNEP-WCMC); NCERT lists 12
- NCERT forest thresholds: evergreen over 200 cm; moist deciduous 100–200 cm; dry deciduous 70–100 cm; thorn under 50 cm
Core Concepts
- Climate decides vegetation, and vegetation decides animals, so the biome map follows the climate map
- Energy flows through an ecosystem and is lost as heat; matter is recycled by decomposers
- Persistent toxins concentrate up the food chain (biomagnification)
- Human emissions exceed what ocean and land sinks absorb, so atmospheric CO₂ rises
- Excess nitrogen and phosphorus cause eutrophication and dead zones
Confused Pairs
- Energy flow (one-way) vs nutrient cycling (circular)
- Food chain (one line) vs food web (interlinked chains)
- Biome (large climate-defined unit) vs ecosystem (any scale, living + non-living)
- Bioaccumulation (within one organism) vs biomagnification (across trophic levels)
- Taiga (coniferous forest, may have permafrost) vs tundra (treeless, permafrost)
PYQ Pattern
- Prelims: biomagnification in a food chain (2010, env-055); India's hotspots (2010, env-054); mangroves (prelims-2026-gs1-033)
- Mains: cellulose decomposition (GS3 2022), carrying capacity (GS3 2019), vegetation diversity (GS1 2023), dead zones (GS1 2018), hot desert location (GS1 2013)
Sources
Sources
- NCERT, Fundamentals of Physical Geography, Class XI, Rationalised Edition, Reprint 2026-27: contents and Ch 14 "Biodiversity and Conservation", kegy214.pdf. The pre-rationalised Ch 15 PDF could not be retrieved.
- NCERT, India: Physical Environment, Class XI, Reprint 2026-27, Ch 5 "Natural Vegetation", kegy105.pdf.
- Friedlingstein, P. et al., "Global Carbon Budget 2025", Earth System Science Data 18, 3211–3288 (2026), doi:10.5194/essd-18-3211-2026; abstract via University of Reading CentAUR.
- Flanders Marine Institute (VLIZ), "Fossil fuel CO2 emissions hit record high in 2025", 12 Nov 2025 (release of the Global Carbon Project's key findings, including tropical forests turning into CO₂ sources), vliz.be.
- IPBES, "Nature's Dangerous Decline 'Unprecedented'; Species Extinction Rates 'Accelerating'", media release, 6 May 2019, ipbes.net.
- Critical Ecosystem Partnership Fund, "Biodiversity Hotspots Defined", Himalaya, Indo-Burma, Sundaland, accessed 1 Oct 2026.
- PIB / MoEFCC, "India's Wildlife Conservation Milestones", 3 Mar 2025, PDF.
- Zhang, N., Yasunari, T. and Ohta, T., "Dynamics of the larch taiga–permafrost coupled system in Siberia under climate change", Environmental Research Letters 6, 024003 (18 Apr 2011), PDF.
- Rantanen, M. et al., "The Arctic has warmed nearly four times faster than the globe since 1979", Communications Earth & Environment (Aug 2022); summary by the University of Eastern Finland.
- UNEP-WCMC list of 17 megadiverse countries, as summarised by the World Economic Forum, June 2024.
- Question banks:
src/_data/mains/pyq/gs1.json,gs3.json;src/_data/pyq-environment-updated.js;src/_data/prelims/2026/gs1.json.
