NCERT Exemplar Solutions Class 12 Biology Ch 13 Biodiversity

Correct option: (a) South America.

Concept used. Biodiversity, the total variety of life at all levels (gene, species, ecosystem), is not spread evenly over the planet. It rises sharply as we move from the poles towards the equator, the latitudinal gradient. Tropical regions get more solar energy, stay warmer and wetter year round, and have been relatively undisturbed for millions of years, so more species could evolve and co-exist there.

1. Among the four options, only South America lies almost entirely inside the tropics. The Amazon basin alone holds more than 40,000 plant species, ∼ 1,300 bird species, ∼ 3,000 fish species and uncounted insects.
2. South Africa lies south of the tropics; Russia spans the boreal and tundra belts, both species-poor. India is megadiverse but a single country, hosting ∼ 8.1% of recorded species on ∼ 2.4% of the world's land area.
3. Comparing the totals: the Amazon biome in South America is the single largest store of terrestrial biodiversity on Earth, far ahead of India's ∼ 45,000 plant + ∼ 91,000 animal species.

Option (a): South America.

Correct option: (c) Keeping animals in zoological parks.

Concept used. The four named drivers of biodiversity loss (the Evil Quartet) are: habitat loss and fragmentation, over-exploitation, alien-species invasion, and co-extinctions. Zoological parks (along with botanical gardens, seed banks and gene banks) are forms of ex situ conservation: they breed and shelter threatened species outside their natural habitat, which prevents extinction rather than causing it.

1. Habitat destruction (a) is the largest single driver: clearing of tropical forests for cropland alone removes ∼ 1% of forest area each year.
2. Alien invasions (b) such as the Nile perch in Lake Victoria wiped out > 200 native cichlid fish; Lantana, water hyacinth and African catfish damage Indian ecosystems.
3. Over-exploitation (d) drove Steller's sea cow, passenger pigeon, and many fishery stocks to extinction or collapse.
4. Zoos (c) keep individuals safe, often re-introduce captive-bred animals (e.g. Asiatic lion at Gir, gharial in Indian rivers), and run gamete banks for future generations. They are a tool of conservation, not loss.

Option (c): Keeping animals in zoological parks is ex situ conservation, not a cause of biodiversity loss.

Correct option: (b) Cynodon.

Concept used. An invasive alien species is one that is introduced (deliberately or accidentally) into an area outside its native range and goes on to spread aggressively, displacing native species. Cynodon dactylon (Bermuda grass, locally called dub or durva) is an Indian native grass, widely present in lawns and pastures across the subcontinent; it is not alien.

1. Lantana (a, Lantana camara): native to Central and South America, introduced as an ornamental, now smothering forest understoreys in the Western Ghats.
2. Parthenium (c, Parthenium hysterophorus, ``carrot grass''): native to tropical America, accidentally introduced with grain shipments in the 1950s, now widespread.
3. Eichhornia (d, Eichhornia crassipes, water hyacinth, ``terror of Bengal''): native to South America, choking water bodies.
4. Cynodon (b): an indigenous grass; the only option among the four that is Indian in origin.

Option (b): Cynodon is an Indian native, not an invasive alien.

Correct option: (a) Rain forest of North-East India.

Concept used. A pitcher plant (genus Nepenthes) is an insectivorous angiosperm whose leaf tip is modified into a fluid-filled pitcher that traps insects, providing nitrogen on the very nutrient-poor (especially nitrogen-poor) soils where it grows. Nepenthes khasiana is the only Indian pitcher plant species and is endemic to the rain forests of Meghalaya in the North-East.

1. Sunderbans (b) is a brackish-water mangrove ecosystem, salt-rich rather than nitrogen-deficient; Nepenthes cannot survive there.
2. Thar Desert (c) is hyper-arid; pitcher plants need a perpetually moist habitat.
3. Western Ghats (d) is a tropical rain-forest hot spot but does not host Nepenthes; that genus in India is restricted to Khasi and Jaintia hills of Meghalaya.
4. North-East India (a) has the right combination: heavy monsoon rainfall, constant humidity, nutrient-leached lateritic soil. Hence Nepenthes khasiana is endemic here.

Option (a): Rain forests of North-East India.

Correct option: (d) Mostly located in the polar regions.

Concept used. Biodiversity hot spots, defined by Norman Myers, are regions with (i) exceptionally high species richness, (ii) a very high proportion of endemic species (found nowhere else), and (iii) serious threat of habitat loss (> 70% of original vegetation already gone). All 34 recognised hot spots are clustered in the tropics and subtropics, never in the polar zones, because the polar zones support comparatively few species and even fewer endemics.

1. Large number of species (a) is one of Myers' two positive criteria.
2. Abundance of endemic species (b) is the other positive criterion; without endemics, a high-richness region is just a rich area, not a hot spot.
3. Tropical location (c) is statistically true: the latitudinal gradient guarantees that high-richness regions cluster near the equator.
4. Polar location (d) is the opposite of (c). Polar regions are species-poor and therefore cannot satisfy Myers' richness criterion.

Option (d).

Correct option: (d) A-iii, B-i, C-iv, D-ii.

Concept used. A small, often-tested set of recently extinct animals demonstrates how local human pressures wipe out endemic species. Each is tied to a single locality.

1. Dodo (Raphus cucullatus): a flightless pigeon endemic to the island of Mauritius (iii). Hunted to extinction by Dutch sailors and their introduced animals by 1681.
2. Quagga (Equus quagga quagga): a half-striped zebra endemic to South Africa (i). Hunted out by 1883.
3. Thylacine (Thylacinus cynocephalus, the Tasmanian wolf): a marsupial carnivore endemic to Tasmania, Australia (iv). Last animal died 1936.
4. Steller's sea cow (Hydrodamalis gigas): a giant sirenian of the Bering Sea, off the coast of Russia / Kamchatka (ii). Hunted out within 27 years of its 1741 discovery.

Option (d): A-iii, B-i, C-iv, D-ii.

Correct option: (c) All are prone to over exploitation.

Concept used. Over-exploitation is the harvesting of a species faster than it can replenish. Plants that supply medicinal alkaloids, decorative foliage, or scientific specimens are particularly vulnerable.

1. Nepenthes khasiana: collected from the wild for ornamental terrariums and curiosity, although it is now legally protected.
2. Psilotum nudum: the ``whisk fern''; collected as a primitive plant of evolutionary interest. Wild stands shrink under pressure.
3. Rauwolfia serpentina: roots harvested for the antihypertensive alkaloid reserpine; populations crashed and the plant is now an Appendix-II CITES species.
4. Aconitum heterophyllum: high-Himalayan medicinal plant (ativisha); over-collected for Ayurvedic and Unani markets.
5. All four are not specifically ornamental, are not all phylogenic links, and are not all confined to Eastern Himalayas (Rauwolfia is peninsular too). The single common thread is over-exploitation pressure.

Option (c): All four species suffer from over-exploitation.

Correct option: (c) Kaziranga.

Concept used. The Indian one-horned rhinoceros (Rhinoceros unicornis) survives in the tall-grass and swampy floodplains of the Brahmaputra and Terai. Kaziranga National Park in Assam holds roughly two-thirds of the species' global wild population, recovering from <200 animals in 1900 to > 2,600 today thanks to strict protection.

1. Bhitar Kanika (a): Odisha mangrove; famous for saltwater crocodile and olive ridley turtles, not rhino.
2. Bandipur (b): Karnataka deciduous forest; tigers and elephants, no rhino.
3. Kaziranga (c): Assam grass–swamp; THE one-horned rhino stronghold.
4. Corbett (d): Uttarakhand foothill forest; tiger reserve, not rhino.

Option (c): Kaziranga.

Correct option: (c) Amphibians.

Concept used. Vulnerability to extinction depends on (i) ecological specialisation, (ii) sensitivity to environmental change, (iii) population size and dispersal ability. Amphibians satisfy all three negatives in the extreme: their permeable skin lets pollutants and UV in directly, their two-stage life-cycle (aquatic larva + terrestrial adult) demands two healthy habitats, and chytrid fungal disease has spread globally.

1. Insects: enormous numbers and rapid reproduction; though many species decline, the group as a whole is resilient.
2. Mammals: many threatened (tigers, primates), but they have widespread protection and behavioural plasticity.
3. Amphibians: IUCN reports ∼ 32% of all amphibian species are threatened with extinction, the highest fraction for any vertebrate class. Many frog species have gone extinct in the last 30 years.
4. Reptiles: vulnerable but not at the amphibian level.

Option (c): Amphibians, the most vulnerable vertebrate class.

Correct option: (d) All of the above.

Concept used. Endangered (EN) in the IUCN Red List is the category just above ``Critically Endangered''. All three named species are listed as endangered in India because of medicinal harvesting, fragrant-wood smuggling, and ornamental over-collection respectively.

1. Rauwolfia serpentina: harvested for the alkaloid reserpine; CITES Appendix II; classified endangered in India.
2. Santalum album (sandalwood): heartwood prized for oil and carving; decades of illegal logging have crashed wild stocks; declared a vulnerable/ endangered species, with felling regulated under State Acts.
3. Cycas beddomei: South Indian endemic gymnosperm, over-collected for ornamental gardens and as a curiosity; listed endangered.
4. All three are recognised on India's endangered list, so the consolidated option (d) is correct.

Option (d): All of the above.

Correct option: (d) All the species are neither threatened nor indigenous species of India.

Concept used. The three named organisms are flagship examples of invasive alien species in India: they are non-native (so not indigenous) and they are spreading aggressively (so not threatened with extinction).

1. Lantana camara: South American shrub, introduced as ornamental, now invades forest understorey.
2. Eichhornia crassipes (water hyacinth): South American free-floating aquatic, chokes water bodies (``terror of Bengal'').
3. African catfish Clarias gariepinus: introduced for aquaculture, outcompetes native Indian catfish in rivers.
4. None are endangered (strike a), none are keystone species (strike b), only the catfish is even an animal (strike c), and all three are alien invaders (option d).

Option (d).

Correct option: (b) Over exploitation by humans.

Concept used. The passenger pigeon (Ectopistes migratorius) was the most abundant bird in North America in the early 19th century, with flocks of billions. Industrial-scale market hunting between 1850 and 1900 reduced it to zero; the last bird, ``Martha'', died in Cincinnati Zoo in 1914. The species is the textbook case of extinction by over-exploitation alone.

1. Predators (a): predatory birds never threatened passenger pigeon numbers because the flocks were too vast.
2. Humans (b): commercial hunters used nets, guns and even sulphur smoke to kill nesting birds by the thousand and ship the carcasses by railway to eastern cities. This is over-exploitation, the recorded cause of extinction.
3. Food shortage (c): although deforestation reduced beech-nut and acorn crops, that pressure followed and was secondary to direct slaughter.
4. Bird flu (d): no evidence; the species was extinct long before bird flu emerged as a recognised problem.

Option (b): Over-exploitation by humans.

Correct option: (c) Steller's sea cow is an extinct animal.

Concept used. The question tests four distinct facts; eliminate three wrong ones to find the only true statement.

1. (a) Parthenium is not endemic; it is an alien from tropical America that became invasive in India. FALSE.
2. (b) African catfish (Clarias gariepinus) escaped from aquaculture farms and outcompetes Indian native catfishes (Clarias batrachus etc.). It is a threat. FALSE.
3. (c) Steller's sea cow (Hydrodamalis gigas) was hunted to extinction by 1768, only 27 years after discovery. TRUE.
4. (d) Carrot grass is the popular name for Parthenium, not Lantana. FALSE.

Option (c).

Correct option: (c) Coral reefs.

Concept used. Coral reefs are the most species-rich marine ecosystems on Earth: although they occupy < 0.1% of the ocean floor, they support an estimated 25% of all marine species, including fish, molluscs, crustaceans, sponges, echinoderms and the reef-building coral animals themselves.

1. Mangroves are diverse but specialised (salt-tolerant, anoxic mud); species count is moderate.
2. Deserts are species-poor by definition: water is the limiting resource.
3. Coral reefs are the marine analogue of tropical rain forests in terms of richness, often called ``rainforests of the sea''.
4. Alpine meadows host a brief summer bloom but are species-poor for most of the year.

Option (c): Coral reefs.

Correct option: (c) Amazon rain forest.

Concept used. The Amazon rain forest covers ∼ 5.5 × 10⁶ km² across nine South American countries. Through photosynthesis it produces an enormous quantity of atmospheric oxygen and absorbs an equally vast amount of CO2: estimates suggest the Amazon contributes about 20% of the world's oxygen and stores ∼ 90--140 billion tonnes of carbon. Hence the nickname ``lungs of the planet''.

1. Taiga (a) is the boreal coniferous belt; photosynthesises only in summer months and is much smaller than the Amazon.
2. Tundra (b) has only mosses, lichens and stunted shrubs; ``tundra forest'' is essentially treeless.
3. Amazon rain forest (c): largest contiguous rainforest, year-round photosynthesis, the textbook ``lungs of Earth''.
4. NE Indian rain forests (d) are biologically rich but tiny in area compared with the Amazon.

Option (c): Amazon rain forest.

Correct option: (b) Rauwolfia.

Concept used. Reserpine is an indole alkaloid first isolated from Rauwolfia serpentina (Sarpagandha) in 1952. It blocks the storage of catecholamines in nerve terminals, lowering blood pressure (antihypertensive) and acting as a tranquilliser.

1. Datura yields tropane alkaloids hyoscyamine and scopolamine, not reserpine.
2. Atropa belladonna yields atropine, not reserpine.
3. Papaver somniferum (opium poppy) yields morphine and codeine, not reserpine.
4. Rauwolfia serpentina yields reserpine. Direct match.

Option (b): Rauwolfia.

Correct option: (d) Fungi.

Concept used. The total recorded species in each group, from the NCERT biodiversity inventory:

1. Gymnosperms: ∼ 1,000 species globally; a small relict group.
2. Algae: ∼ 40,000 species across all algal divisions.
3. Bryophytes: ∼ 17,000 species (mosses, liverworts, hornworts).
4. Fungi: ∼ 72,000 described species (NCERT) and an estimated ∼ 1.5 million total, by far the largest of the four groups.

Option (d): Fungi.

Correct option: (a) Tropics.

Concept used. The tropics (latitudes ≤ 23.5^∘) receive near-vertical sunlight year round; day length, mean temperature and rainfall vary relatively little month-to-month, giving a ``constant'' environment. The temperate zone, by contrast, shows a strong four-season cycle, and alpine regions show extreme winter–summer swings.

1. Tropics: small seasonal variation (a few degrees in temperature, but a wet/dry rhythm in some regions). Generally the least variable.
2. Temperate zone: pronounced winter–summer cycle (> 20^∘C swing).
3. Alpine zone: large daily and seasonal temperature swings; snow cover in winter.
4. Therefore (a) is uniquely correct; (b) cannot be combined with (a), ruling out (d).

Option (a): Tropics.

Correct option: (b) The Earth Summit.

Concept used. The United Nations Conference on Environment and Development held in Rio de Janeiro in June 1992 is popularly called the Earth Summit. It opened for signature the Convention on Biological Diversity (CBD), the first global treaty committing nations to conserve biodiversity, use its components sustainably, and share genetic-resource benefits fairly.

1. CITES (a): Convention on International Trade in Endangered Species, signed 1973 in Washington, regulates trade. Different treaty.
2. Earth Summit (b): 1992 Rio meeting; produced CBD plus Agenda 21 and the UN Framework Convention on Climate Change. Match.
3. G-16 Summit (c): no such recognised body.
4. MAB (d): Man and Biosphere programme of UNESCO, started 1971, designates biosphere reserves. Different programme.

Option (b): The Earth Summit.

Correct option: (b) All are ex situ conservation methods.

Concept used. Ex situ conservation preserves threatened species outside their natural habitat, in zoos, botanical gardens, gene banks, cryopreservation tanks (-196^∘C liquid nitrogen) or tissue-culture labs. In situ conservation, by contrast, protects species inside their natural habitat (national parks, sanctuaries, biosphere reserves).

1. In vitro fertilisation (IVF): gametes are combined outside the body to produce embryos for endangered species. Ex situ.
2. Cryopreservation: gametes, embryos, seeds stored at -196^∘C in liquid nitrogen. Ex situ.
3. Tissue culture: somatic cells grown on agar to regenerate whole plants. Ex situ.
4. All three happen outside the natural habitat, so they are ex situ. They do not all need ultra-modern equipment in vast space, and they cannot revive truly extinct organisms.

Option (b): All are ex situ conservation methods.

Concept used. A stable community is one whose total productivity, species composition and ecosystem services vary little across years. Tilman's long- term Cedar Creek experiments showed that the three properties that confer stability are: low year-to-year variation in productivity, resistance to occasional disturbance, and resistance to invasions by alien species.

1. It should not show too much variation in productivity from year to year.
2. It must be either resistant or resilient to occasional disturbances such as fire or drought.
3. It must also be resistant to invasions by alien species. A community in which these three are true is by Tilman's definition stable.

Constant productivity + disturbance resistance/resilience + invasion resistance.

Concept used. A mass extinction is a brief geological interval in which a large fraction (>50%) of species disappears. Five such events are recorded in fossil history. Their triggers, identified from rock and isotopic evidence, are large-scale, sudden environmental perturbations.

1. Asteroid or comet impact (Cretaceous–Palaeogene event, ∼ 65 million years ago, ended the dinosaurs).
2. Massive volcanic eruptions (Siberian Traps at the Permian–Triassic boundary, ∼ 252 million years ago).
3. Sudden global climate change (warming or cooling) that altered sea level, ocean chemistry and atmospheric CO2.
4. Catastrophic changes in oceanic oxygen or pH (ocean anoxia, acidification).

Asteroid impact, mass volcanism, abrupt climate change and ocean-chemistry crashes.

Concept used. India is one of the world's 12 megadiverse countries. Its richness comes from extreme physical and climatic variety packed into a single subcontinent.

1. Geographic range: from snow-bound Himalayas in the north to coral-fringed seas in the south, and from the arid Thar in the west to the wet North-East.
2. Climatic range: tropical, subtropical, temperate and alpine climates all occur, often within a few hundred kilometres.
3. Diverse biomes / habitats: tropical rain forest, mangroves, deserts, coral reefs, wetlands, grasslands, alpine meadows, all are present.
4. Long evolutionary history with the Indian plate's movement contributing ancient endemic lineages.

Wide latitudinal, altitudinal and climatic range + many distinct biomes + long evolutionary history.

Concept used. Tilman's rule is a positive correlation observed in natural communities. Humans can break this by adding fertiliser, irrigation, pesticide and energy subsidies to a monoculture (a single-species crop field), pushing its productivity up despite its very low diversity.

1. Examples: a paddy field of a single rice variety, a wheat field, a sugarcane field, a hybrid-maize plantation, a single-clone teak or eucalyptus plantation.
2. Productivity is high because all inputs (light, water, NPK, weed control) are tuned to one species.
3. Such systems are productive but fragile: a single pest or disease outbreak can collapse the harvest, the very fragility Tilman warned about.

Agricultural monocultures, e.g. rice, wheat, sugarcane fields.

Concept used. The IUCN Red List is the global inventory of the conservation status of species. The colour ``Red'' signals danger: it is the warning colour of biological alarm, used here for species facing extinction.

1. ``Red'' indicates species which are threatened with extinction across the world, i.e. in the Critically Endangered, Endangered and Vulnerable categories.
2. The 2004 list catalogued ∼ 15,500 such species: > 12% of all birds, ∼ 23% of mammals, ∼ 32% of amphibians and ∼ 31% of gymnosperms.

``Red'' denotes species threatened with extinction (CR + EN + VU).

Concept used. Biodiversity hot spots are regions that are simultaneously (i) very rich in species, (ii) very rich in endemic species, and (iii) under severe threat. Because endemics are nowhere else, loss of their habitat means global extinction.

1. Of the 34 globally recognised hot spots, the total land cover is < 2% of Earth's surface. Three of them lie partly in India: the Western Ghats–Sri Lanka, Himalaya, and Indo-Burma.
2. Yet they harbour an extremely high concentration of endemic species, with the small extra of a large fraction of total terrestrial biodiversity.
3. Protecting just these small areas would save the species that would otherwise vanish; ecologists estimate that this single action could cut the global extinction rate by up to 30%.
4. The cost-benefit ratio is therefore extraordinary: a small fraction of land protects a huge fraction of species.

Hot spots = endemic-rich tiny areas; protecting them prevents disproportionately many extinctions, ∼ 30%.

Concept used. Both terms describe the geographic origin of a species, but in opposite directions.

1. Endemic species: native to and found only in a particular geographical region, e.g. Nepenthes khasiana (Meghalaya), Bos gaurus (Indian gaur), Asiatic lion (Gir).
2. Exotic species: introduced from elsewhere, not native to the area, e.g. Lantana, Water hyacinth, African catfish in India.
3. Endemics are biogeographically restricted; exotics are biogeographic transplants.

Endemic = native and restricted; exotic = introduced from outside.

Concept used. Species diversity is biodiversity at one level (the species); ecological diversity is biodiversity at a higher level (the ecosystem).

1. Species diversity is the variety of species in a given area, captured by species count (species richness) and relative abundance.
2. Ecological diversity is the variety of ecosystems / habitats / community types in a region (e.g. forest, grassland, desert, wetland, mangrove, coral reef).
3. Example: India's ∼ 45,000 plant + ∼ 91,000 animal species is species diversity; the fact that India contains rain forest, mangrove, desert, coral reef, alpine meadow and tundra is ecological diversity.

Species diversity = variety within species; ecological diversity = variety of ecosystems / habitats.

Concept used. Genetic variation within a species means different populations carry different alleles and produce different concentrations or chemical variants of secondary metabolites.

1. Rauwolfia vomitoria is the source of reserpine, an antihypertensive alkaloid.
2. Different populations of the plant produce different concentrations and chemical variants of reserpine, because of their different gene make-up.
3. Conserving this genetic variation is therefore essential for the pharmaceutical industry: it ensures access to high-yield, high-potency strains and protects against losing the chemotype that supplies modern medicine.

Genetic variation produces variation in reserpine yield and chemotype, which is critical for drug supply.

Concept used. The Red Data Book is an official catalogue maintained by IUCN that records the conservation status of plant, animal, fungal and other taxa: which are extinct, which are threatened (CR, EN, VU), and which are at lower risk.

1. It compiles, for each listed species, the cause(s) of decline, distribution and current population status.
2. It is updated periodically (the online version is now called the IUCN Red List) and is the authoritative reference used by governments and treaties.

Official IUCN catalogue of the conservation status of species.

Concept used. The gene pool of a population is the complete set of all alleles of all genes present in all individuals of an interbreeding population at a given time.

1. It includes every allele variant for every locus in the population.
2. A large, diverse gene pool gives the population the raw genetic material on which natural selection can act, raising adaptability.
3. A shrunken gene pool (small population, inbreeding) reduces adaptability and raises extinction risk.

Sum of all alleles of all genes of all individuals in an interbreeding population.

Concept used. Frugivorous comes from Latin frux (fruit) and vorare (to eat). It describes an animal whose diet is composed mainly or entirely of fruit.

1. Examples: hornbills, parrots, fruit bats, many primates, civets.
2. Frugivores are crucial seed dispersers: by eating fruit and defecating intact seeds far from the parent tree, they keep forest regeneration going.

Frugivorous = fruit-eating.

Concept used. IUCN is the global authority on the conservation status of species, headquartered in Gland, Switzerland.

1. I = International.
2. U = Union for.
3. C = Conservation of.
4. N = Nature (and Natural Resources, in full).
5. Together: International Union for Conservation of Nature and Natural Resources, founded 1948.

International Union for Conservation of Nature (and Natural Resources).

Concept used. Two ecological / economic terms.

1. (i) Bioprospecting: the systematic exploration of biodiversity for new genes, molecules, chemicals or products of commercial value (drugs, dyes, enzymes, agrochemicals). It is one of the strongest economic arguments for conserving biodiversity, especially in tropical hot spots.
2. (ii) Endemism: the property of being native to and restricted to a particular geographic region. Endemic species are highly vulnerable because their entire global population lives in a small area, e.g. Nepenthes khasiana in Meghalaya.

Bioprospecting = mining biodiversity for useful products. Endemism = restriction of a species to a single region.

Concept used. The two plants pictured are Lantana camara (A) and Parthenium hysterophorus (B), both invasive alien species of India. They have no native presence here and damage the ecosystems they invade.

1. Lantana camara: South/Central American shrub introduced as an ornamental, now smothers forest undergrowth, especially in the Western Ghats and Shivalik foothills.
2. Parthenium hysterophorus (carrot grass, congress grass): a tropical American annual herb, accidentally introduced with imported wheat in the 1950s, now widespread on roadsides, fallow lands and forest edges.
3. Common features: both are non-native (alien), both spread aggressively (invasive), both reduce native species richness, and both are listed among India's worst invasives.

Both A and B are invasive alien plant species of India that displace native vegetation.

Concept used. Figure A shows a Bengal tiger (Panthera tigris tigris) and figure B shows the Quagga (Equus quagga quagga) or a similar ungulate from the NCERT extinction plate. The pair makes the contrast between an endangered species (tiger) and an extinct species (Quagga, extinct since 1883).

1. Tiger: Panthera tigris, the apex predator of Indian forests; currently endangered, with ∼ 3,500 wild individuals worldwide.
2. Quagga: a half-striped zebra subspecies of southern Africa; hunted to extinction in the 19th century. Its name comes from the call it made.
3. Common feature: both have suffered severe population decline due to human hunting and habitat destruction; both are wild mammals victims of human exploitation. The tiger is on the brink, the Quagga has already crossed over.

Both are large mammals driven into severe decline by human hunting: the tiger is endangered, the Quagga is already extinct.

Concept used. Both events involve large losses of species, but they differ in cause, speed and reversibility. The present is sometimes called the Sixth Extinction or Holocene Extinction.

1. Cause. Past mass extinctions were triggered by natural catastrophes (asteroid impact, mass volcanism, abrupt climate change). The present extinction is caused almost entirely by a single species, Homo sapiens: habitat destruction, hunting, alien introductions, pollution and climate change.
2. Rate. Past mass extinctions, although they look ``sudden'' in geological time, played out over 10⁴–10⁶ years. The present rate is 100 to 1,000 times the natural background rate, and the most species-rich groups are being hit fastest.
3. Time scale of recovery. Past extinctions were followed by natural recovery and radiation over ∼ 10⁷ years. The present extinction is so fast that recovery, even if pressure were removed today, would take millions of years.
4. Reversibility. Past events were unstoppable natural processes. The present extinction is preventable: it can be slowed by conservation action.

Present extinction is anthropogenic, ∼ 100–1,000 times faster than the background rate, and (uniquely) preventable.

Concept used. The Evil Quartet of biodiversity loss is habitat loss and fragmentation, over-exploitation, alien-species invasion and co-extinctions. Among them, habitat loss and fragmentation is the single biggest driver.

1. Habitat loss strips the physical home of resident species at one stroke. Tropical forests, once ∼ 14% of Earth's land, have shrunk to ∼ 6%.
2. The Amazon, called the ``lungs of the planet'', is being cleared at rates that threaten its tipping point. The same story is repeated in Southeast Asian rain forests, mangrove belts, and grasslands.
3. Fragmentation breaks the remaining habitat into small, isolated patches. Large mammals, top carnivores and migratory birds lose viable territories, gene flow drops, and small populations face local extinction.
4. Pollution often pushes still-marginal populations over the edge.
5. Because habitat loss attacks the very stage on which species live, it outweighs the other three drivers in total impact.

Habitat loss and fragmentation: it destroys the substrate of life, making all other pressures lethal.

Concept used. Co-extinction is the secondary extinction of one species that follows the loss of a species it depends on, especially in obligate mutualisms.

1. Example: a tightly co-evolved plant–pollinator pair, e.g. certain fig species pollinated by a single species of fig wasp. If that wasp is lost, the fig cannot set seed and goes extinct in turn.
2. Day-to-day observation: when local nesting trees of fruit-bats are cut down, the bats decline; the bat-pollinated baobab and durian trees stop producing fruit, and the bat-dependent dispersers and human harvesters lose their resource.
3. In Indian context: vulture decline (caused by the cattle drug diclofenac) is leading to crashes in vulture-dependent feral dog and rat populations being unchecked, with onward effects on carcass disposal and rabies.

Co-extinction follows when a species loses its sole partner; e.g. fig–fig wasp.

Concept used. Alexander von Humboldt's species–area relation on a log–log plot is a straight line: log S = log C + Z log A, S = C A^Z. The slope Z measures how fast species accumulate with area. Empirical work shows Z depends on the spatial scale.

1. For small areas within a single biogeographic region, Z = 0.1–0.2. New species are added slowly because nearby patches share most species.
2. For very large areas (whole continents, oceans, the planet), Z rises steeply to 0.6–1.2.
3. Reason: a very large area straddles many distinct biomes and biogeographic provinces, each with its own pool of endemic species. Every new biome added contributes a whole fresh set of species, so the curve climbs faster.

Large areas span many biomes, each with endemics, so Z rises from ∼ 0.15 to ∼ 0.9.

Concept used. A natural community is a dynamic ecosystem: populations grow and crash, succession changes the species pool, and external disturbances (fire, drought, flood) reshape both productivity and diversity.

1. Strict constancy over 100 years is unrealistic for any natural community.
2. Even an undisturbed climax community shows year-to-year fluctuations driven by climate (ENSO cycles), seasonal pulses, and stochastic deaths.
3. Long-term experiments (Tilman, Cedar Creek; Park Grass at Rothamsted) show productivity and diversity both fluctuate, though they may stay within bounded limits.
4. Disturbance (fires, floods, droughts, alien invasions) can shift the community to a new state.

No; productivity and diversity always fluctuate over decadal time scales.

Concept used. The latitudinal gradient in species richness is the single strongest biogeographic pattern: species per unit area is highest at the equator and falls towards the poles. Three reasons (proposed by Pianka and discussed in NCERT) explain it.

1. Evolutionary time. Tropical regions have had relatively undisturbed environments for millions of years; temperate regions suffered repeated Pleistocene glaciations. Tropical species have had much longer time to evolve and diversify.
2. Constant environment. Tropics are warm and humid year round, with low seasonality. Niche specialisation is therefore easier and more species can coexist.
3. Greater solar energy. The equatorial belt receives the most intense solar radiation, supporting higher primary productivity, which in turn supports more consumer biomass and more consumer species.

Long undisturbed evolutionary time + constant environment + higher solar energy = more species in the tropics.

Concept used. Conventional taxonomic methods rely on visible morphological characters, but bacteria show very few morphological differences between species. Most bacteria cannot be cultured in the laboratory.

1. Bacteria are tiny, mostly cocci or bacilli; classical morphology can distinguish only broad groups.
2. More than 99% of bacterial species cannot be grown on standard culture media (the ``great plate-count anomaly'').
3. Species identification therefore requires molecular techniques such as 16S rRNA gene sequencing, DNA–DNA hybridisation, or metagenomic sequencing of environmental samples.
4. Hence the true species count of bacteria is only estimable by these non-conventional methods.

Morphology gives few characters and most bacteria cannot be cultured, so molecular (DNA-based) methods are required.

Concept used. The IUCN uses a set of quantitative Red List criteria (A–E) to assess whether a species is Critically Endangered, Endangered or Vulnerable.

1. Rate of population decline over the last 10 years or 3 generations.
2. Geographic range size (extent of occurrence and area of occupancy).
3. Total population size (number of mature individuals).
4. Population fragmentation and number of locations.
5. Probability of extinction in the wild within a defined time frame, based on quantitative analysis.

Population decline, range size, total population, fragmentation, extinction probability.

Concept used. Amphibians have a unique biology that exposes them simultaneously to multiple environmental stressors.

1. Permeable, naked skin: absorbs water, gases, pollutants and UV-B directly from the environment; toxins and pathogens enter easily.
2. Bi-phasic life cycle: aquatic larva (tadpole) plus terrestrial adult means two habitats must remain healthy at once. Loss of either is enough to crash the population.
3. External fertilisation in moist conditions: requires very specific water bodies; pollution or drying eliminates breeding.
4. Chytrid fungus (Batrachochytrium dendrobatidis): a globally spreading pathogen that has driven ∼ 100 species to extinction in 30 years.
5. Net effect: ∼ 32% of all amphibians are threatened, the highest proportion of any vertebrate class.

Permeable skin + bi-phasic life cycle + water-bound breeding + chytrid disease = exceptional vulnerability.

Concept used. About 1.8 million species have been recorded so far, but the true total is much larger. Scientists extrapolate from intensively sampled, species-rich groups using statistical relationships.

1. One robust method (Robert May): for well-studied groups like birds and mammals, the ratio of described tropical to described temperate species is recorded. Apply that ratio to less-studied groups (insects, invertebrates, fungi) to estimate the true tropical total.
2. Another method: count species in intensively sampled small plots (canopy fogging of a tropical tree gives 1,200–3,000 beetles, for example) and scale up.
3. Combining methods, Robert May arrived at a conservative estimate of ∼ 7 million total species on Earth; other estimates run from 5 to 30 million.

Use the temperate-to-tropical species ratio from well-studied groups + intensive plot sampling, then scale up.

Concept used. The economic and ecosystem-service value of biodiversity is enormous, ranging from direct products to indirect services.

1. Medicines: ∼ 25% of modern prescription drugs come from plants. Examples: taxol (anti-cancer) from Taxus brevifolia, artemisinin (antimalarial) from Artemisia annua, reserpine (antihypertensive) from Rauwolfia serpentina, morphine from Papaver somniferum.
2. Food: the entire human diet (cereals, pulses, fruits, vegetables, dairy, fish, poultry) is harvested from biodiversity. New crop varieties are developed by cross-breeding cultivated crops with their wild relatives.

Medicines (taxol, artemisinin, reserpine) and food (cereals + wild crop relatives).

Concept used. Anthropogenic (human-caused) drivers dominate, but natural drivers also contribute.

1. Catastrophic geological events: volcanic eruptions, earthquakes, tsunamis, large meteorite impacts can wipe out local biotas instantly.
2. Abrupt natural climate change: ice ages, glacial–interglacial transitions, sudden ocean-current shifts. Past mass extinctions (Permian–Triassic, Cretaceous–Palaeogene) were driven by such events.

Catastrophic geological events and abrupt natural climate change.

Concept used. An endangered species is one whose numbers have fallen to a critical level: it is likely to become extinct in the near future if the present pressures continue. It is the IUCN category just above Critically Endangered.

1. Plant example: Rauwolfia serpentina (Sarpagandha), over-harvested for the reserpine alkaloid; or Santalum album (Indian sandalwood), over-logged for fragrant heartwood.
2. Animal example: Panthera tigris (Bengal tiger), with ∼ 3,500 wild individuals globally; or the Asiatic lion (Panthera leo persica) restricted to Gir, Gujarat.

Endangered = likely extinct soon without action. Plant: Rauwolfia. Animal: Tiger.

Concept used. Sacred groves are tracts of forest that local human communities have preserved on religious grounds, dedicating them to local deities. Cutting or hunting inside such groves is taboo, often for centuries.

1. Examples: Khasi and Jaintia hills in Meghalaya, Aravalli hills (Rajasthan, Gujarat), Western Ghats (Karnataka, Maharashtra), Sarguja, Chanda, and Bastar areas of Madhya Pradesh.
2. Role: undisturbed groves act as living refugia for native flora and fauna, including rare and threatened endemics that have vanished from the surrounding agricultural landscape.
3. Sacred groves are a form of community-led in situ conservation, complementary to national parks and sanctuaries.

Sacred groves = religion-protected forest tracts that act as community- managed in situ refuges for biodiversity.

Concept used. The three habitats are coastal: coral reefs grow in clear tropical shallow seas, mangroves grow at the inter-tidal river mouths, estuaries are the transition zones where rivers meet the sea.

1. Andaman and Nicobar Islands: home to Indian fringing and barrier coral reefs (Mahatma Gandhi Marine National Park, Wandoor; Rani Jhansi Marine NP), large mangrove formations, and many small estuarine creeks.
2. Alternative single sites: Gulf of Mannar (Tamil Nadu) for coral reef, Sunderbans (West Bengal) for mangroves, Chilika lagoon (Odisha) for estuarine ecology.

Andaman & Nicobar Islands offer all three; alternatively Gulf of Mannar + Sunderbans + Chilika.

Concept used. The tropics (23.5^∘ N to 23.5^∘ S) lie either side of the equator and receive sunlight closest to vertical year round.

1. Sun's rays strike the equator nearly perpendicular throughout the year. The same amount of solar radiation is spread over a smaller area than at higher latitudes, where the rays strike obliquely.
2. Therefore solar-flux density (W/m²) is highest at the equator and decreases towards the poles.
3. Day length is also more uniform in the tropics (∼ 12 h all year), whereas the polar regions have months of darkness.
4. Higher solar energy supports higher primary productivity, more diverse ecosystems, and is one reason why the tropics are biologically richest.

Yes; near-vertical sun + uniform day length give the tropics the highest solar input per unit area.

Concept used. Co-extinction is the secondary extinction of a species that follows the loss of a species it depends on. It is one of the four drivers in the Evil Quartet.

1. Mechanism: in obligate mutualisms, loss of one partner removes a resource the other cannot replace. Examples include pollinator-flower and parasite-host relationships.
2. Example: when a fish species in a marine reef goes extinct, the gut-parasites and ecto-parasites unique to that fish vanish with it.
3. Another example: many tropical plants depend on a single species of pollinator. If the pollinator goes, the plant cannot set seed and goes too. Conversely, plant extinction starves the specialist herbivores.

Co-extinction = obligate-partner-driven secondary extinction; e.g. parasites following their host, or a plant following its only pollinator.

Concept used. An invasive alien species is a non-native species that establishes, spreads, and reduces native diversity through several ecological mechanisms.

1. Competitive exclusion. Aliens often arrive without their natural enemies (predators, parasites, diseases) from home. With unchecked growth they outcompete native species for light, water, nutrients or space. Example: Eichhornia crassipes (water hyacinth) covers ponds in dense mats, blocking sunlight, lowering dissolved oxygen, and killing native aquatic flora and fauna.
2. Predation. An alien predator may find native prey that has evolved no defences against it. Example: introduction of Lates niloticus (Nile perch) into Lake Victoria, East Africa, drove > 200 endemic cichlid fish species to extinction.
3. Disease transmission. Aliens can carry pathogens to which natives have no immunity. Example: chytrid fungus Batrachochytrium dendrobatidis spread to amphibian populations worldwide, with ∼ 100 species lost.
4. Habitat alteration. Aliens can change the chemistry, structure or fire regime of an ecosystem, displacing natives. Example: Lantana camara forms dense thickets that smother native forest undergrowth and alter fire frequency.
5. Hybridisation. Aliens may interbreed with closely related natives, swamping the native gene pool. Example: Clarias gariepinus (African catfish) introduced in Indian rivers hybridises with and outcompetes native Clarias batrachus.

Aliens reduce diversity through competitive exclusion, predation, disease, habitat alteration and hybridisation.

Concept used. Individual conservation action works at three scales: lifestyle choices that reduce one's ecological footprint, direct support of biodiversity programmes, and advocacy / education.

1. Reduce, reuse, recycle. Cut consumption of paper, plastic and packaging. Lower demand means less habitat conversion.
2. Plant native trees, particularly in your garden, school or neighbourhood; native trees support far more native birds and insects than ornamental exotics.
3. Avoid products that drive biodiversity loss: ivory, fur, coral jewellery, exotic-wood furniture, illegally caught wild meat or pet animals.
4. Choose sustainable seafood and certified palm-oil products; avoid items that fund habitat destruction.
5. Save water and energy; lower personal carbon and water footprint reduces climate-driven biodiversity loss.
6. Do not litter, especially in wild areas; participate in local clean-up drives.
7. Support conservation organisations and biosphere reserves through volunteering and donations; visit protected areas responsibly to boost local conservation economies.
8. Spread awareness: discuss biodiversity with family and friends, write to local representatives about wildlife habitat issues.

Eight individual actions reduce loss: footprint, native planting, boycott of wildlife products, sustainable choices, water/energy saving, no littering, supporting conservation orgs, and advocacy.

Concept used. David Tilman's long-term plot experiments at Cedar Creek, Minnesota, gave the first rigorous quantitative support for the diversity–stability hypothesis. The scientific reasons are functional complementarity and the insurance effect.

1. Tilman found that plots with more species showed less year-to-year variation in total biomass and higher overall biomass production.
2. Niche complementarity. Different species use slightly different portions of the resource base (light, water, soil nitrogen at different depths). When all are present they together extract more of the available resource than any single species could alone.
3. The insurance effect (statistical averaging). Stress (drought, heat, pathogen) hits different species differently. In a diverse community, some species suffer while others compensate. In a monoculture a single stress can devastate the whole community.
4. Increased trophic interactions. More species means more herbivores, predators and decomposers, which buffer each other against booms and crashes.
5. Empirically, Tilman's plots with > 16 species showed half the coefficient of variation in productivity compared with monoculture plots.

Diversity raises stability through niche complementarity + statistical insurance against species-specific stress + denser trophic interactions, as shown by Tilman's Cedar Creek experiments.

Concept used. Human-wildlife conflict arises when growing human populations push into shrinking wildlife habitats, leading to crop damage, livestock losses, human injuries, and retaliatory wildlife killings. The intensity has multiplied because modern activities have multiplied the points of contact.

1. Historical baseline. Early humans hunted some species and were hunted by others, but population density was low and habitat largely intact, so conflict was localised.
2. Population explosion and agriculture. Modern human numbers (∼ 8 billion) have converted most arable land into cropland, shrinking wildlife habitat and forcing elephants, monkeys, wild boars, leopards and tigers to raid crops and livestock.
3. Linear infrastructure. Roads, railways and power lines slice wildlife corridors. In India ∼ 200 elephants are killed each year by train collisions in Assam, West Bengal and Odisha; leopards stray into cities along railway lines.
4. Loss of prey base. Hunting and habitat loss have crashed wild ungulate numbers; large carnivores (tiger, leopard, snow leopard) move into villages to take livestock and occasionally humans.
5. Climate change and resource scarcity. Droughts force elephants and gaur to range outside protected areas in search of water and fodder, bringing them into farms.
6. Examples. (i) Elephant–human conflict in Assam (annual loss ∼ 200 humans + ∼ 100 elephants); (ii) leopard incursions in Mumbai's Sanjay Gandhi NP fringe colonies; (iii) wolf attacks in Bahraich (UP); (iv) tiger conflict in Sunderbans where rising sea levels intrude on human settlements.

Population pressure, habitat fragmentation, linear infrastructure, prey loss and climate change have multiplied human-wildlife contact and conflict intensity.

Concept used. Ecosystem services are the benefits people obtain, free of charge, from the functioning of healthy ecosystems. Robert Costanza's 1997 paper estimated the global value of ecosystem services at ∼ 33 trillion a year, roughly twice the world's GDP at the time.

steps Definition. Ecosystem services are the goods (food, water, fibre, medicines) and regulatory functions (climate stabilisation, nutrient cycling, pollination, flood control, cultural and aesthetic value) supplied by intact ecosystems. Four important services. (a) Pollination: by bees, butterflies, birds, bats. Around 75% of food crops depend on animal pollinators. (b) Climate regulation: tropical rain forests are major carbon sinks; the Amazon stores 100$ billion tonnes of carbon. (c) Water purification and flood control: wetlands and riparian forests filter pollutants and absorb floodwaters. (d) Soil formation and nutrient cycling: decomposer communities recycle dead biomass into nutrients available to plants. Other services include cultural and aesthetic value, recreation, and scientific knowledge. Should we charge for ecosystem services? A balanced view: I favour charging commercial consumers (industries that draw bulk groundwater, log forests, dump effluent into rivers) because internalising the cost forces them to reduce damage and finances restoration. I do not favour charging poor rural communities for whom these services are subsistence-level (firewood, drinking water, grazing). Mechanisms include carbon credits, payments for watershed protection, biodiversity offsets, and tradable permits. India's Compensatory Afforestation Fund and Ecosystem Services Improvement Project follow this logic. steps

Ecosystem services = free benefits from healthy ecosystems (pollination, climate, water, nutrient cycling). Charge commercial consumers but not subsistence consumers.

Concept used. Consumptive use value is the direct economic value of biodiversity products that are consumed without being marketed. NCERT groups these into food, drugs and medicines, fuel and fibre.

1. Food. Wild and cultivated plants and animals supply every human diet: cereals (rice, wheat, maize, millet), pulses (gram, arhar, urad), vegetables (potato, tomato, brinjal), fruits (mango, banana, citrus), animal products (milk, egg, meat, fish), spices (pepper, cardamom, turmeric). Wild relatives of crops are a source of disease-resistance and yield-improvement genes used in plant breeding.
2. Drugs and medicines. About 25% of modern prescription drugs derive from plants. Examples: taxol (anti-cancer) from Taxus brevifolia; artemisinin (antimalarial) from Artemisia annua; reserpine (antihypertensive) from Rauwolfia serpentina; morphine and codeine (analgesics) from Papaver somniferum; digoxin (cardiac) from Digitalis purpurea; quinine (antimalarial) from Cinchona officinalis. Traditional Ayurvedic and Unani systems use thousands of plant species.
3. Fuel. ∼ 2.4 billion people worldwide still rely on biomass (firewood, dung, crop residue, charcoal) for cooking. India, Sub-Saharan Africa and SE Asia depend heavily on plant biomass; fossil fuels (coal, petroleum, natural gas) are themselves transformed remains of ancient biodiversity.
4. Fibre. Plant fibres: cotton (Gossypium), jute (Corchorus), linen (Linum), hemp (Cannabis). Animal fibres: wool (sheep), silk (silkworm Bombyx mori). These supply clothing, sacking, ropes and paper industries worldwide. Timber (Tectona, Shorea, Pinus) supplies construction, furniture and paper.

Consumptive use spans food (crops, livestock, fish), drugs (25% of prescriptions), fuel (biomass for ∼ 2.4 billion), and fibre (cotton, jute, silk, wool).

Concept used. This pattern is the latitudinal gradient, the strongest biogeographic regularity in ecology. NCERT (following Pianka) gives three reasons.

1. Evolutionary time. Tropical latitudes have remained relatively undisturbed for millions of years, while temperate and polar regions were repeatedly glaciated during the Pleistocene. Tropical species have had far longer evolutionary time to speciate and accumulate.
2. Constant, predictable environment. The tropics are warm and humid year round, supporting niche specialisation and stable coexistence of many species. Temperate environments swing between extremes; only generalist species cope.
3. Greater solar energy. The equatorial belt receives the highest solar-energy flux, driving the highest primary productivity. More plant biomass supports more herbivores, more carnivores, more decomposers, and therefore more species at every trophic level.
4. Additional factors. (i) Larger area of the tropical belt compared with high-latitude belts gives more space for species to evolve. (ii) Less environmental harshness reduces extinction rates. (iii) Greater habitat heterogeneity (forest canopy layers, coral reef tiers).

Evolutionary time + environmental constancy + solar energy + area + habitat heterogeneity together explain the latitudinal gradient.

Concept used. The Rivet Popper Hypothesis, proposed by ecologist Paul Ehrlich, is an analogy that explains why species loss matters even when each individual extinction looks small.

1. Imagine an airplane held together by thousands of rivets. Every passenger (analogous to humanity) pops one rivet on each flight to sell as a souvenir. The first few rivets popped from non-critical positions seem harmless: the plane keeps flying.
2. By analogy, every species in an ecosystem is a rivet. Removing a non-keystone species causes a small, easily-missed loss of function; ecosystem services continue largely unchanged.
3. But there is a critical threshold: too many rivets popped and the plane suddenly disintegrates. Equally, after enough species are lost, the ecosystem collapses catastrophically.
4. Some rivets matter more than others: rivets on a wing are more critical than rivets on the seats. Likewise, loss of a keystone species (top predator, sole pollinator, ecosystem engineer like the beaver or elephant) is much more damaging than loss of a redundant species.
5. The hypothesis carries two messages: (i) we should not gamble with species loss because we cannot tell in advance which species are critical rivets; (ii) the catastrophic collapse is non-linear and sudden, not gradual.

Each species is a rivet; losing a few may seem harmless, but at a critical threshold the ecosystem collapses suddenly. Keystone species are the most critical rivets.

Concept used. The species–area relationship states that species richness S rises with sampled area A following a power law S = C A^Z, log S = log C + Z log A, where C is a constant (depends on taxon and region) and Z is the slope of the log–log line. On linear axes this power law plots as a rectangular hyperbola-like rising curve that flattens at large A.

1. Alexander von Humboldt observed during his explorations of South America that as area surveyed grew, the number of plant species also grew, but more and more slowly.
2. Plotting S against A on linear axes gives an upward-curving line whose slope decreases as A rises: the rectangular-hyperbola-type relation.
3. Why the curve bends: in a small area, every patch encountered is likely to add new species (low overlap). As area grows, most species in the new patch are already counted, so the marginal addition shrinks.
4. The same relationship plotted on log–log axes is a straight line with slope Z, Z = 0.1–0.2 at small scales within one biogeographic region, Z = 0.6–1.2 at very large scales (continents).
5. The pattern holds across taxa: angiosperms in California, birds of the West Indies, freshwater fish in Amazonia, mammals of the Indian subcontinent.

The species–area relation S = C A^Z rises steeply at first and flattens, producing a rectangular-hyperbola-shaped curve; on log–log axes the same data form a straight line of slope Z.