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State Board · Class 12 · Biology

Lesson 15: Biodiversity, Conservation and Environmental Issues

7 concepts · 56 practice questions with answers · Free to read

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Levels and patterns of biodiversity

Link to Std 9–10

Last lesson covered energy and nutrients in ecosystems; here we learn biodiversity, its conservation and environmental issues such as pollution.

From daily life

Many stalls at a fair — the more kinds, the richer the fair.

Simple definition

Biodiversity = total variety of genes, species and ecosystems. Term by Walter Rosen (1982).

BiodiversityLevels and patterns of biodiversityGeneticwithin speciesSpeciesspecies richnessEcosystemecosystemsBiodiversity = genes + species + ecosystems; term: Walter Rosen (1982)Genetic: about 1000 mango and 50 000 rice/wheat varietiesSpecies diversity: richness + evenness; e.g. amphibiansLatitudinal gradient: more species toward the equatorAltitudinal gradient: decreases with altitudeSpecies–area: Von Humboldt; S = C·Aᶻ; Z ≈ 0.1–0.2Tropical rain forest: Amazon 40 000 plants, 1300 birds, 427 mammals

In the figure : Levels and patterns.

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Levels and patterns of biodiversity

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Rule 1 : Three levels — Genetic diversity: variety of genes/alleles within a species — about 1000 mango and 50 000 rice/wheat varieties; Himalayan medicinal plants vary in chemical content by location. Species diversity: number (richness) and distribution (evenness) of species; India is among 15 rich nations. Ecosystem diversity: forests, deserts, estuaries, wetlands, coral reefs; high in the Western Ghats, lower in the Rann of Kutch.

  • Easy : Three levels.
  • Medium : Richness + evenness.
  • Exam-type (CET) : Rice has 50 000 varieties.

Rule 2 : Patterns — Latitudinal gradient: more species toward the equator, fewer toward poles — stable climate, more solar energy, larger area. Altitudinal gradient: decrease with height. Species–area relationship (Von Humboldt): species rise with area; rectangular hyperbola; straight line on log scale log S = log C + Z log A; Z usually 0.1–0.2; for very large areas (continents) Z 0.6–1.2. E.g. Amazon rain forest: 40 000 plants, 1300 birds, 427 mammals.

  • Easy : Equator = more.
  • Medium : Z ≈ 0.1–0.2.
  • Exam-type (CET) : Humboldt = species–area.
Remember

G-S-E: genes, species, ecosystems.

Common mistake and CET trap

‘More species at the poles’ is wrong. Trap: ‘Z is 5’ is wrong.

Shortcut

Memory clue : "Equator = most species".

Spot the difference

LevelExample
Genetic1000 mango varieties
SpeciesIndia among 15 rich
EcosystemForest, estuary

Practice questions

Easy
  1. 1Term coined by?
  2. 2Three levels?
  3. 3Evenness means?
Medium
  1. 4More species where?
  2. 5Usual Z?
  3. 6Humboldt studied?
Challenging
  1. 7Rice varieties?
  2. 8Altitude effect?
Show answers (try them yourself first)
  1. 1Walter Rosen 1982.
  2. 2Genetic, species, ecosystem.
  3. 3Distribution of species.
  4. 4Near equator.
  5. 50.1–0.2.
  6. 6Species–area.
  7. 7About 50 000.
  8. 8Species decrease.

Importance and current scenario

From daily life

A farmer growing many crops survives even if one fails.

Simple definition

Megadiversity country = species-rich nation; India is one of 12. Rivet popper hypothesis = each species is like a rivet in a plane.

ScenarioImportance and current scenarioSpeciesknown ~1.8 millionIndia2.4% of landStabilityTilmanKnown about 1.5–1.8 million; estimated 20–50 million existAnimals ~1.3 million; plants ~287 000India: one of 12 megadiversity countries; ~45 000 plants; about twice as many animalsBy May's estimate only ~22% recordedTilman: more diversity → stable biomass, less variationEhrlich: ‘rivet popper’ — each species like a rivet of an aeroplaneAmboli ghat lizard: Hemidactylus varadgirii (identified by DNA)

In the figure : Importance and scenario.

Rule 1 : Species in the world and India — About 1.5–1.8 million species recorded; animals ~1.3 million, plants ~287 000. The true number may be 20–50 million (May's estimate; higher in tropical forests). India: 2.4% of world land yet among 12 megadiversity countries; ~45 000 plants, about twice as many animals; by May's estimate only 22% recorded. Risk of loss before recording; need for taxonomists. E.g. an Amboli ghat lizard re-identified by DNA profiling as Hemidactylus varadgirii.

  • Easy : India has 2.4% of the land area.
  • Medium : 12 megadiversity.
  • Exam-type (CET) : 22% identified.

Rule 2 : Diversity and stability — David Tilman's experiments: plots with more species show less year-to-year biomass variation, better drought tolerance, more resistance to invasives. Paul Ehrlich's rivet popper: losing a few rivets from a plane does little at first; losing key rivets causes a crash. So species loss is not linear; loss of key species is quickly dangerous.

  • Easy : Tilman = stability.
  • Medium : Ehrlich = rivet.
  • Exam-type (CET) : Key species are important.
Remember

Diversity = insurance.

Common mistake and CET trap

‘Species loss always has equal impact’ is wrong. Trap: ‘India has the largest land area’ is wrong (2.4%).

Shortcut

Memory clue : "Tilman = stable over time; Ehrlich = rivets".

Spot the difference

ScientistIdea
TilmanDiversity → stability
EhrlichRivet popper
May20–50 million species

Practice questions

Easy
  1. 1Known species?
  2. 2India's land share?
  3. 3Number of megadiversity countries?
Medium
  1. 4Plants in India?
  2. 5Tilman showed?
  3. 6Rivet popper by?
Challenging
  1. 7% of Indian life recorded?
  2. 8Taxonomists do?
Show answers (try them yourself first)
  1. 11.5–1.8 million.
  2. 22.4%.
  3. 312.
  4. 4About 45 000.
  5. 5Diversity gives stability.
  6. 6Paul Ehrlich.
  7. 7About 22%.
  8. 8Identify and classify species.

Loss of biodiversity and IUCN

From daily life

News says the Great Indian Bustard is nearly gone — a species fading away.

Simple definition

Extinction = complete loss of a species. Red Data Book / Red List = IUCN record of threat status.

LossLoss of biodiversityHabitat lossmain causeOverexploitover-useAlien speciesinvasiveCo-extinctionlinkedExtinction: natural, mass, man-madeSix mass extinctions occurred; now the 7th, 100–1000× fasterAlien/invasive: carrot grass (Parthenium), Lantana, water hyacinth; Nile perchCo-extinction: parasite/host, flower/pollinatorIUCN Red List: Extinct, Extinct in the Wild, CR, EN, VU, NT, LCE.g. Great Indian Bustard — last in Maharashtra 2018Human–wildlife conflict: leopard, elephant; compensation

In the figure : Causes of loss.

Rule 1 : Extinction and causes — Types: natural, mass, man-made. Earth has had six mass extinctions (e.g. Cretaceous–Tertiary); the present loss is the seventh, 100–1000 times faster than pre-human times. Four causes: (1) habitat loss and fragmentation (main; e.g. Amazon forest, jhum/slash-burn); (2) over-exploitation (hunting, over-fishing — bustard); (3) alien/invasive species (carrot grass, Lantana, water hyacinth; Nile perch wiped out ~200 cichlid fishes of Lake Victoria); (4) co-extinction (host–parasite, flower–pollinator).

  • Easy : Six mass extinctions.
  • Medium : Habitat loss is the main cause.
  • Exam-type (CET) : Co-extinction = together.

Rule 2 : IUCN Red List — IUCN threat categories: Extinct, Extinct in the Wild, Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened, Least Concern. Criteria: population decline, range size, small numbers. E.g. Great Indian Bustard — last in Maharashtra in 2018; now Rajasthan, Gujarat. Human–wildlife conflict (leopard, elephant): compensation, driving off with trained elephants, safe corridors.

  • Easy : CR = most endangered.
  • Medium : IUCN = Red List.
  • Exam-type (CET) : Great Indian Bustard = grassland.
Remember

HOAC: habitat, over-exploitation, alien, co-extinction.

Common mistake and CET trap

‘Present loss is natural’ is wrong (man-made). Trap: ‘invasive = native species’ is wrong.

Shortcut

Memory clue : "HOAC = habitat, over-use, alien, co-extinction".

Spot the difference

CauseExample
Habitat lossFire, deforestation
AlienLantana, carrot grass
Co-extinctionFlower–pollinator

Practice questions

Easy
  1. 1Current extinction is?
  2. 2How much faster?
  3. 3Main cause?
Medium
  1. 4Nile perch caused?
  2. 5Red List by?
  3. 6CR means?
Challenging
  1. 7Bustard now in?
  2. 8Co-extinction?
Show answers (try them yourself first)
  1. 1Seventh.
  2. 2100–1000 times.
  3. 3Habitat loss.
  4. 4Cichlid extinction.
  5. 5IUCN.
  6. 6Critically Endangered.
  7. 7Rajasthan, Gujarat.
  8. 8Linked loss.

Conservation: in situ, ex situ and BD Act

From daily life

Saving home seeds — protection for the future.

Simple definition

In situ = protection in the natural habitat. Ex situ = protection outside the habitat. A hotspot = species-rich, threatened region.

ConservationConservationIn situnatural habitatEx situoutside habitatBD Act2002Reasons: narrowly utilitarian, broadly utilitarian, ethicalIn situ: national park, sanctuary, biosphere reserve, hotspots, sacred groves34 hotspots; India has 4: Western Ghats, Indo-Burma, Sundaland, Eastern HimalayaIndia: 14 biosphere reserves, 90 national parks, 448 sanctuariesEx situ: zoos, botanical gardens, seed banks, cryopreservation (−196°C)BD Act 2002: NBA → SBB → BMC; fine up to ₹10 lakh without permissionRahibai Popere — ‘seed mother’; 54 crops, 116 varieties

In the figure : Ways of conservation.

Rule 1 : Why and how — Reasons: narrowly utilitarian (food, medicine — 25% of the global drug market; bioprospecting), broadly utilitarian (oxygen, pollination; Amazon ~20% O₂), ethical (every living being's right to live). In situ: national parks, sanctuaries, biosphere reserves, sacred groves; 34 hotspots; India has 4 — Western Ghats, Indo-Burma, Sundaland, Eastern Himalaya; protecting them could cut extinction by ~30%. India has 14 biosphere reserves, 90 national parks, 448 sanctuaries; Maharashtra 5 national parks, 11 sanctuaries.

  • Easy : 4 hotspots in India.
  • Medium : 34 in the world.
  • Exam-type (CET) : Sacred groves = in situ.

Rule 2 : Ex situ and BD Act 2002 — Ex situ: zoos, safari parks, botanical gardens, crocodile bank, seed banks; modern: tissue culture, IVF, cryopreservation (−196°C) of gametes. Biological Diversity Act 2002 (under CBD 1992; Rio Earth Summit): three tiers — NBA (national), SBB (state), BMC (local). Using biological resources needs NBA permission; NBA has civil-court powers; offenders face jail and a fine up to ₹10 lakh. Miyawaki method: dense native plantations; Rahibai Popere (‘seed mother’) — 54 crops, 116 varieties.

  • Easy : NBA → SBB → BMC.
  • Medium : −196°C.
  • Exam-type (CET) : Fine of 10 lakh.
Remember

In = inside the habitat; ex = outside.

Common mistake and CET trap

‘Zoo is in situ’ is wrong (ex situ). Trap: ‘India has 34 hotspots’ is wrong (4; world 34).

Shortcut

Memory clue : "In situ = inside; ex situ = exit".

Spot the difference

MethodExample
In situNational park, sacred grove
Ex situZoo, seed bank
BD ActNBA, SBB, BMC

Practice questions

Easy
  1. 1Hotspots in India?
  2. 2World hotspots?
  3. 3Cryopreservation temperature?
Medium
  1. 4BD Act year?
  2. 5NBA stands for?
  3. 6Fine?
Challenging
  1. 7Sacred groves are?
  2. 8‘Seed mother’?
Show answers (try them yourself first)
  1. 14.
  2. 234.
  3. 3−196°C.
  4. 42002.
  5. 5National Biodiversity Authority.
  6. 6₹10 lakh.
  7. 7In situ conservation.
  8. 8Rahibai Popere.

Air pollution

From daily life

In traffic jams eyes sting and we cough.

Simple definition

A pollutant = substance/energy harming health. PM2.5 = particles 2.5 μm or smaller.

Air pollutionAir pollutionPM2.5fine particlesCOincomplete burningNO₂/SO₂acidityCO₂greenhouseParticulate: smoke, smog, dust, heavy metals; PM2.5 goes deep into lungsCO binds haemoglobin; vehicle exhaustElectrostatic precipitator: ~99% of particles; negative particles to positive platesScrubber: water/lime for SO₂; catalytic converter: CO, HC, NOx → CO₂, H₂O, N₂Catalytic converter needs unleaded petrol (lead poisons catalyst)Delhi: buses on CNG (2002); Bharat Stage (BS II → BS VI)Ujjwala (2016): LPG — less household smoke; EPA 1986

In the figure : Air pollutants and control.

Rule 1 : Pollutants and effects — Particulates: smoke, smog, dust, heavy metals, pesticides; 10 μm particles settle; 1 μm or less remain suspended; PM2.5 most harmful — deep in lungs, inflammation, breathing disorders. Gaseous: CO₂ (greenhouse), CO (incomplete combustion; vehicles; binds haemoglobin), SO₂, NO/NO₂ (nitric acid with water; irritates eyes and lungs). Reduces crop yield. Regulation: Environment Protection Act 1986; CPCB.

  • Easy : PM2.5 is the most harmful.
  • Medium : CO = incomplete combustion.
  • Exam-type (CET) : EPA 1986.

Rule 2 : Control measures — Electrostatic precipitator: high voltage ionises air; particles become negatively charged and stick to positive plates; removes about 99% of particles from a thermal plant. Scrubber: spray of water/lime removes SO₂. Catalytic converter: CO, hydrocarbons, NOx → CO₂, H₂O, N₂; needs unleaded petrol (lead deactivates catalyst). Delhi: all buses on CNG by 2002; Bharat Stage (BS II to BS VI, Euro-equivalent); Ujjwala (2016): LPG for BPL women ⇒ less household smoke and CO. Car-pooling, public transport.

  • Easy : ESP 99%.
  • Medium : Converter = unleaded.
  • Exam-type (CET) : CNG = clean.
Remember

ESP = electric; scrubber = spray; converter = catalyst.

Common mistake and CET trap

‘Catalytic converter uses leaded petrol’ is wrong. Trap: ‘PM10 is most harmful’ is wrong (PM2.5).

Shortcut

Memory clue : "PM2.5 reaches deep into lungs".

Spot the difference

DeviceJob
PrecipitatorRemoves particles
ScrubberRemoves SO₂
Catalytic converterCuts CO, NOx

Practice questions

Easy
  1. 1Most harmful particle size?
  2. 2Why CO harmful?
  3. 3ESP efficiency?
Medium
  1. 4Fuel for converter cars?
  2. 5Delhi buses use?
  3. 6Ujjwala gives?
Challenging
  1. 7EPA year?
  2. 8Scrubber uses?
Show answers (try them yourself first)
  1. 1PM2.5.
  2. 2Binds haemoglobin.
  3. 3About 99%.
  4. 4Unleaded.
  5. 5CNG.
  6. 6LPG connections.
  7. 71986.
  8. 8Water / lime.

Water pollution and biomagnification

From daily life

Green scum and dead fish in a lake — a sick water body.

Simple definition

BOD = oxygen needed to break down organic matter. Biomagnification = rising concentration of a toxin up a food chain.

Water pollutionWater pollution and biomagnificationBODorganic loadEutrophicationalgal bloomBiomagnificationDDTThermalhot waterHigh BOD = more organic pollution, less dissolved O₂Eutrophication (cultural): N, P, sewage → algae → O₂ drop → fish dieBiomagnification: DDT — water 0.000003 → zooplankton 0.04 ppm→ small fish 0.5 → large fish 2 → fish-eating birds 25 ppmEffect: thin egg shells in birds; population declineThermal pollution: hot effluent → low O₂, sensitive species dieEcoSan toilets; plastic ban (Maharashtra 23 June 2018); e-waste recycling

In the figure : BOD, eutrophication, biomagnification.

Rule 1 : BOD and eutrophication — Even about 0.1% impurity can make water unfit. High BOD ⇒ more organic pollution, less dissolved O₂. Eutrophication: lakes naturally enrich slowly; fertilisers, sewage and detergents speed it up — cultural/accelerated eutrophication — algal bloom ⇒ O₂ drop ⇒ fish die. Thermal pollution: hot factory water ⇒ low O₂, sensitive species lost. EcoSan toilets: fertiliser from excreta; saves water.

  • Easy : High BOD = polluted.
  • Medium : Cultural = fast.
  • Exam-type (CET) : Warm water = O₂ drop.

Rule 2 : Biomagnification and waste — DDT ~0.000003 ppm in water ⇒ zooplankton 0.04 ⇒ small fish 0.5 ⇒ large fish 2 ⇒ fish-eating birds 25 ppm — it is not metabolised so it accumulates; thin egg shells, chick deaths, population decline. Waste: separate biodegradable and recyclable; e-waste contains heavy metals — recycle at proper units; plastic ban in Maharashtra on 23 June 2018. Buy responsibly and use less.

  • Easy : DDT 0.000003 → 25 ppm.
  • Medium : Thin shell.
  • Exam-type (CET) : e-waste = heavy metals.
Remember

DDT climbs: 0.000003 → 25.

Common mistake and CET trap

‘Biomagnification is highest at the base’ is wrong (top). Trap: ‘eutrophication cleans water’ is wrong.

Shortcut

Memory clue : "Top predator = toxic peak".

Spot the difference

LevelDDT (ppm)
Water0.000003
Small fish0.5
Fish-eating birds25

Practice questions

Easy
  1. 1High BOD means?
  2. 2Cultural eutrophication due to?
  3. 3DDT in birds?
Medium
  1. 4DDT effect on birds?
  2. 5Thermal pollution cause?
  3. 6Plastic ban Maharashtra?
Challenging
  1. 7e-waste contains?
  2. 8EcoSan toilets give?
Show answers (try them yourself first)
  1. 1More pollution.
  2. 2Fertilisers, sewage.
  3. 325 ppm.
  4. 4Thin egg shells.
  5. 5Hot effluent.
  6. 623 June 2018.
  7. 7Heavy metals.
  8. 8Manure.

Greenhouse effect, global warming and ozone depletion

From daily life

A closed car in the sun gets hot inside — a greenhouse example.

Simple definition

Greenhouse effect = gases trap heat and keep earth warm. Ozone depletion = thinning of the ozone layer by CFCs.

Greenhouse, ozoneGreenhouse effect and ozone depletionCO₂fossil fuelsCH₄paddy, cattleCFCAC, extinguisherN₂OagricultureGreenhouse gases: CO₂, CH₄, CFC, N₂O, water vapourRe-emitted heat returns to earth — like a glasshouseEarth warmed ~0.6°C in last century; mostly last 3 decadesEffects: El Niño, melting ice, coastal floodingOzone depletion: CFC + UV → Cl; Cl breaks ozone down (catalyst)‘Ozone hole’ over AntarcticaRemedies: less fossil fuel, tree planting, efficiency; Chewang Norphel's artificial glaciers

In the figure : Greenhouse and ozone depletion.

Live figure

Greenhouse effect, global warming and ozone depletion

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Open in the app

Rule 1 : Greenhouse and global warming — The atmosphere admits sunlight but blocks earth's infrared; CO₂, CH₄, CFC, N₂O and water vapour absorb and send it back — the greenhouse effect. Sources: fossil fuels, burning of farm waste (CO₂); biogas, paddy fields, cattle sheds (CH₄); ACs, fire extinguishers (CFC). Global warming: earth warmed about 0.6°C in the last century, mostly in the last three decades. Effects: El Niño, melting polar/Himalayan ice, coastal flooding. Remedies: less fossil fuel, energy efficiency, stop deforestation, tree planting, population control. E.g. Chewang Norphel (Ladakh) built 13 artificial glaciers.

  • Easy : 0.6°C rise.
  • Medium : CO₂, CH₄, CFC, N₂O.
  • Exam-type (CET) : El Niño = effect.

Rule 2 : Ozone depletion — Stratospheric ozone absorbs UV-B. CFCs rise, and under UV release Cl atoms; Cl breaks ozone into O₂ and, as a catalyst, remains unchanged and acts again and again. Marked depletion over Antarctica — the ozone hole. Effects: skin cancer, cataract, crop damage. Remedy: ban on CFCs (Montreal Protocol) and substitutes. World Ozone Day 16 September; Environment Day 5 June; Earth Day 22 April.

  • Easy : Cl = catalyst.
  • Medium : Ozone Day: 16 September.
  • Exam-type (CET) : CFC = ozone enemy.
Remember

CFC → Cl → ozone falls.

Common mistake and CET trap

‘The ozone hole causes the greenhouse effect’ is wrong (different). Trap: ‘no greenhouse gases would make earth hotter’ is wrong.

Shortcut

Memory clue : "Ozone: UV shield; 16 September".

Spot the difference

IssueCause
Global warmingCO₂, CH₄
Ozone holeCFC
EutrophicationN, P

Practice questions

Easy
  1. 1A greenhouse gas?
  2. 2Warming in last century?
  3. 3CFC source?
Medium
  1. 4Ozone layer in?
  2. 5World Ozone Day?
  3. 6Role of Cl?
Challenging
  1. 7El Niño is?
  2. 8Artificial glaciers by?
Show answers (try them yourself first)
  1. 1CO₂ / CH₄.
  2. 2About 0.6°C.
  3. 3AC, extinguisher.
  4. 4Stratosphere.
  5. 516 September.
  6. 6Catalyst.
  7. 7Pacific climate cycle.
  8. 8Chewang Norphel.

Quick revision of the whole lesson

ConceptKey fact
LevelsGenetic, species, ecosystem
India2.4% land; 12 megadiversity
LossHOAC; seventh extinction
ConservationIn/ex situ; 4 hotspots; BD Act 2002
AirPM2.5; ESP 99%; BS norms
WaterBOD; DDT 25 ppm
Climate0.6°C; CFC → ozone hole

🎯 Most important points for the exam

  • Levels and patterns.
  • Importance and scenario.
  • Loss and IUCN.
  • Conservation and BD Act.
  • Air pollution.
  • Water pollution, biomagnification.
  • Greenhouse and ozone depletion.
Study mantra

Understand the concept → draw the figure → memorise the key points → solve questions yourself.