Biodiversity and its Conservation ISC Class 12 Biology: Notes

What Biodiversity and its Conservation is about

Weightage: Biodiversity and its Conservation is part of the unit Ecology and Environment, which carries 15 of the 70 marks in the ISC Biology Paper 1 (Theory), shared with 2 other chapters. Questions on it can appear in any section of the paper.Source: CISCE ISC Biology syllabus, examination year 2027, distribution of marks

Key concepts

Levels of biodiversity and global numbers

Genetic diversity: a single species may show high diversity at the genetic level over its distribution. Rauwolfia vomitoria in different Himalayan ranges varies in the potency and concentration of the chemical reserpine; India has more than 50 000 genetically different strains of rice and 1000 varieties of mango. Species diversity: diversity at the species level; the Western Ghats have greater amphibian species diversity than the Eastern Ghats. Ecological diversity: diversity at the ecosystem level; India, with deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows, has greater ecosystem diversity than a Scandinavian country like Norway. How many species? IUCN (2004) put the total described plant and animal species at slightly more than 1.5 million; Robert May's estimate of global species diversity is about 7 million. Proportions: more than 70% of all recorded species are animals, plants (algae, fungi, bryophytes, gymnosperms, angiosperms) are about 22%; among animals, insects are the most species-rich group (more than 70% of the total animals). The number of fungi species exceeds the combined total of fish, amphibians, reptiles and mammals. Prokaryote diversity is hard to estimate because conventional methods cannot identify many of them. India: 2.4% of the world's land area but about 8.1% of species diversity; one of 12 mega-diversity countries; about 45 000 plant and twice as many animal species recorded.

Worked example

Give one example each of genetic, species and ecological diversity from India.

Try it first, then show the solutionSolution

1. Genetic: over 50 000 strains of rice (or varying reserpine in Rauwolfia vomitoria).
2. Species: more amphibian species in the Western Ghats than in the Eastern Ghats. Ecological: deserts, rainforests, mangroves, coral reefs and alpine meadows within one country.

Answer: As above

Patterns of biodiversity: latitudinal gradient and species-area relationship

Latitudinal gradient: species diversity decreases from the equator towards the poles. Tropics (23.5° N to 23.5° S) have more species: Colombia (near the equator) has nearly 1400 bird species, New York (41° N) 105, Greenland (71° N) 56; India, largely tropical, has more than 1200 bird species. The Amazon rainforest has the greatest biodiversity on Earth. Why tropics are richer: (1) speciation is a function of time: temperate regions were subjected to frequent glaciations, while tropical latitudes remained undisturbed for millions of years, giving a long evolutionary time for diversification; (2) tropical environments are less seasonal, relatively constant and predictable, promoting niche specialisation; (3) more solar energy is available, contributing to higher productivity. Species-area relationship (Alexander von Humboldt): within a region, species richness increases with explored area, but only up to a limit. The relation is a rectangular hyperbola: $S=C{A}^Z$, or on a log scale a straight line: $\log S=\log C+Z\log A$, where S = species richness, A = area, Z = slope of the line (regression coefficient), C = Y-intercept. Ecologists found Z ≈ 0.1-0.2 for smaller areas regardless of taxonomic group or region; for very large areas such as entire continents, Z is much steeper, 0.6-1.2 (e.g. frugivorous birds and mammals in tropical forests of different continents, Z = 1.15).

Worked example

For a region C = 4 and Z = 0.2. Estimate the species richness for an area of 10 000 km².

Try it first, then show the solutionSolution

1. $S=C{A}^Z=4\times 10000^{0.2}$
2. $10000^{0.2}=10^{0.8}=6.31$; S = 4 × 6.31 = 25.2

Answer: About 25 species

Importance of biodiversity: rivet popper hypothesis and reasons to conserve

Is species diversity important for ecosystems? David Tilman's long-term plot experiments showed that plots with more species had less year-to-year variation in total biomass, and that increased diversity contributed to higher productivity: communities with more species tend to be more stable. Rivet popper hypothesis (Paul Ehrlich): an ecosystem is compared to an aeroplane (airplane) and its species to the rivets joining its parts. If every passenger pops a rivet to take home (species become extinct), the plane may not be affected at first (safe flight), but as more rivets are removed it becomes dangerously weak. Which rivet is removed also matters: losing rivets on the wings (key species that drive major ecosystem functions, like keystone species) is a more serious threat than losing a few on the seats or windows. Why conserve: Narrowly utilitarian: humans derive countless direct economic benefits: food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and medicines (more than 25% of drugs are derived from plants; 25 000 plant species are used in traditional medicine). Bioprospecting explores molecular, genetic and species-level diversity for products of economic importance. Broadly utilitarian: biodiversity provides ecosystem services: the Amazon forest produces about 20% of the total oxygen in Earth's atmosphere through photosynthesis; pollination by bees, bumblebees, birds and bats (without which plants cannot make fruits or seeds); aesthetic pleasures (walking through forests, watching birds, spring flowers). Ethical: every species has an intrinsic value, even if not of economic value; we have a moral duty to care for their well-being and pass on our biological legacy to future generations.

Worked example

What is bioprospecting, and why can countries rich in biodiversity, such as India, gain from it?

Try it first, then show the solutionSolution

1. Bioprospecting is the exploration of molecular, genetic and species-level diversity for products of economic importance (medicines, crop genes, industrial chemicals).
2. Biodiversity-rich nations hold more of these resources, so with proper benefit-sharing they can earn from them, a narrowly utilitarian reason for conservation.

Answer: Searching biodiversity for useful products; rich countries hold more such resources

Loss of biodiversity: extinctions and causes

The IUCN Red List (2004) documented the extinction of 784 species in the last 500 years. Recent extinctions: dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia) and three subspecies of tiger (Bali, Javan, Caspian). The last twenty years alone saw the disappearance of 27 species. Some groups (amphibians) appear more vulnerable. Earth has had five episodes of mass extinction; the current, sixth extinction is 100-1000 times faster than pre-human background rates and is due to human activities. Effects of loss: decline in plant production, lowered resistance to environmental perturbations such as drought, increased variability in ecosystem processes (plant productivity, water use, pest and disease cycles). Causes ('the evil quartet'): (1) Habitat loss and fragmentation: most important cause; tropical rainforests once covered 14% of the land surface, now no more than 6%; the Amazon is being cut for soybean cultivation and cattle grassland; fragmentation of large habitats harms animals needing large territories (mammals, birds) and migratory animals. (2) Over-exploitation: 'need' turning into 'greed': Steller's sea cow and passenger pigeon were over-exploited; many marine fish are over-harvested. (3) Alien species invasions: intentionally or unintentionally introduced species may become invasive: the Nile perch introduced into Lake Victoria caused the extinction of more than 200 species of cichlid fish; carrot grass (Parthenium), Lantana and water hyacinth (Eichhornia); illegal introduction of the African catfish Clarias gariepinus threatens native catfish. (4) Co-extinctions: when a species becomes extinct, plants and animals obligatorily associated with it also become extinct: parasites of an extinct host fish; co-evolved plant-pollinator mutualisms.

Worked example

Explain with examples how alien species and co-extinction cause loss of biodiversity.

Try it first, then show the solutionSolution

1. Alien species: Nile perch introduced into Lake Victoria wiped out more than 200 cichlid species; Parthenium, Lantana and Eichhornia displace native plants.
2. Co-extinction: extinction of a host fish also eliminates its unique parasites; loss of a pollinator dooms the plant that depends on it.

Answer: As above

In-situ conservation: protected areas, hotspots and Ramsar sites

In situ (on site): protecting species in their natural habitat, conserving the whole ecosystem. Biodiversity hotspots: regions with very high species richness, high endemism (species found nowhere else) and under threat. Initially 25 were identified; now 34 worldwide. Three cover India's rich regions: Western Ghats and Sri Lanka, Indo-Burma and the Himalaya (plus Sundaland, which includes the Nicobar Islands). Together the hotspots cover less than 2% of Earth's land area yet hold a very large share of species; strict protection could reduce ongoing mass extinctions by almost 30%. Protected areas in India: biosphere reserves (with a core zone with no human activity, a buffer zone with limited activity such as research and education, and a transition zone with human settlements and sustainable use), national parks (strictly protected for wildlife; no private rights, no grazing or cultivation; e.g. Jim Corbett, Kaziranga), wildlife sanctuaries (protection of fauna; some human activities such as collection of forest products and grazing may be allowed). Sacred groves: tracts of forest set aside by tribal communities for religious reasons, protecting all trees and wildlife: Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghats (Karnataka, Maharashtra), Sarguja, Chanda and Bastar (Madhya Pradesh/Chhattisgarh). In Meghalaya they are the last refuges for many rare and threatened plants. Ramsar sites: wetlands of international importance under the Ramsar Convention (1971, Ramsar, Iran), e.g. Chilika Lake (Odisha), Keoladeo National Park (Rajasthan), Wular Lake (Jammu and Kashmir), Loktak Lake (Manipur), Sundarbans (West Bengal).

Worked example

Distinguish between a national park and a wildlife sanctuary, and name the three zones of a biosphere reserve.

Try it first, then show the solutionSolution

1. National park: area strictly reserved for wildlife; no human activities like grazing, cultivation or forestry. Sanctuary: protection mainly for fauna; some activities (collecting forest produce, grazing) may be permitted.
2. Biosphere reserve zones: core (undisturbed), buffer (limited research and education), transition (settlements and sustainable use).

Answer: As above

Ex-situ conservation and the Red Data Book

Ex situ (off site): threatened animals and plants are taken out of their natural habitat and protected in special settings. Zoological parks, botanical gardens and wildlife safari parks serve this purpose; captive breeding of endangered species in zoos (many animals extinct in the wild are maintained in zoological parks) with later release into the wild. Cryopreservation: gametes of threatened species are preserved in viable and fertile condition for long periods at very low temperatures (liquid nitrogen, −196 °C). Eggs can be fertilised in vitro, and plants propagated by tissue culture. Seed banks store seeds of commercially important plants for long periods. Red Data Book (Red List): a catalogue maintained by the IUCN (International Union for Conservation of Nature) of species facing the risk of extinction, with categories such as extinct, extinct in the wild, critically endangered, endangered and vulnerable; its purpose is to list and document endangered (threatened) species to guide conservation. International efforts: the Earth Summit (Convention on Biological Diversity) was held at Rio de Janeiro in 1992; it called upon all nations to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits (with fair and equitable sharing of benefits). The World Summit on Sustainable Development was held at Johannesburg, South Africa, in 2002, where 190 countries pledged to achieve, by 2010, a significant reduction in the current rate of biodiversity loss at global, regional and local levels.

Worked example

Why are seed banks and cryopreservation called ex-situ methods? Give one limitation of ex-situ conservation compared with in-situ conservation.

Try it first, then show the solutionSolution

1. They protect species away from their natural habitat: seeds or gametes are stored under controlled conditions (cryopreservation in liquid nitrogen at −196 °C).
2. Limitation: only a small part of a species' genetic diversity is held, and the ecosystem and the species' interactions are not conserved (captive animals may also lose natural behaviour).

Answer: Conservation outside the habitat; it cannot preserve the whole ecosystem or full genetic diversity

Biodiversity and its Conservation in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Importance of Biodiversity and the Rivet Popper Hypothesis
• Patterns of Biodiversity
• Biodiversity Conservation and Biopiracy

Biodiversity and its Conservation: key facts

Species-area relationship

$S=C{A}^Z,\log S=\log C+Z\log A$

Z ≈ 0.1-0.2 (small areas); 0.6-1.2 (continents).

Ratio of species for two areas

$\frac{S_2}{S_1}={\left(\frac{A_2}{A_1}\right)}^Z$

Same C and Z.

India's share

$2.4\%\text{of land area},8.1\%\text{of species}$

One of 12 mega-diversity countries.

Evil quartet

$\text{habitat loss}+\text{over-exploitation}+\text{alien species}+\text{co-extinction}$

Causes of biodiversity loss.

Conventions

$\text{Ramsar 1971 (Iran)};\text{Earth Summit 1992 (Rio)};\text{World Summit 2002 (Johannesburg)}$

Wetlands; CBD; reduce loss by 2010.

Biosphere reserve zones

$\text{core}\to \text{buffer}\to \text{transition}$

Increasing human activity outwards.

Biodiversity and its Conservation: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Biodiversity and its Conservation

The question patterns to expect, and the method that works for each.

Tricks to remember Biodiversity and its Conservation

Short memory aids. Say each one aloud once, then use it on a question the same day.

• The evil quartet: HOAC

  Habitat loss, Over-exploitation, Alien species, Co-extinction.

  Use it when: Causes of loss.

• Rivets on wings

  Ecosystem = aeroplane; species = rivets; wing rivets = key species (Ehrlich).

  Use it when: Rivet popper hypothesis.

• Rio 92, Jo'burg 02

  Earth Summit in Rio 1992; World Summit in Johannesburg 2002.

  Use it when: Conventions.

• Narrow = goods, Broad = services

  Narrowly utilitarian: products (food, drugs); broadly utilitarian: ecosystem services (oxygen, pollination).

  Use it when: Reasons to conserve.

• DQ-TS-BJC

  Recent extinctions: Dodo, Quagga, Thylacine, Steller's sea cow, Bali, Javan, Caspian tigers.

  Use it when: Extinct species list.

Biodiversity and its Conservation: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In the board paper this is a 5-mark question split into 1 + 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Biodiversity and its Conservation

The slips examiners see most often, and what to write instead.

• ✗Mistake: Wrong species-area arithmetic

  CISCE examiners' comments, 2024: in a table with area, Y-intercept and regression coefficient for Africa and Europe, candidates divided instead of multiplying C and A, wrote the formula without calculating, named the wrong continent as more diverse, and described conservation methods instead of factors that increase biodiversity.

  Wrong working

  S = A/C

  Right working

  S = C × A^Z (with Z = 1, S = C × A); compare the values.

  ✓Do this: Write S = CA^Z, substitute, compute, then compare.

  Usually costs: 1-2 marks.

• ✗Mistake: Incomplete rivet popper and utilitarian answers

  CISCE examiners' comments, 2025: candidates could not explain the analogy of species as rivets, the ecosystem as an aeroplane and wing rivets as key species, misspelt Paul Ehrlich, and repeated 'narrowly/broadly utilitarian' without listing resources or interchanged the examples.

  Wrong working

  Narrowly utilitarian: oxygen from forests.

  Right working

  Narrowly: food, timber, medicines (direct products). Broadly: oxygen, pollination, aesthetic value (services).

  ✓Do this: Goods = narrow; services = broad.

  Usually costs: 1-2 marks.

• ✗Mistake: Guessing dates and agendas

  CISCE examiners' comments, 2025: candidates guessed the year of the Earth Summit, mixed it with other environmental events, gave a vague agenda or introduced global warming, and in an MCQ chose 'identify areas for conservation' as the purpose of the Red Data Book.

  Wrong working

  Earth Summit 1972 on global warming.

  Right working

  Rio de Janeiro, 1992: conservation of biodiversity and sustainable use of its benefits; Red Data Book lists threatened species.

  ✓Do this: Learn the three conventions as a table: name, place, year, agenda.

  Usually costs: 1 mark each.

• ✗Mistake: Growth-rate formula errors and confusing biopiracy

  CISCE examiners' comments, 2025: for species increasing from 1000 by 200 in 5 years, candidates used an incorrect growth-rate formula or made arithmetic errors; asked to explain biopiracy, they left out authorisation and permission, gave wrong definitions, or confused biopatent with biopiracy.

  Wrong working

  Growth rate = 1200/5.

  Right working

  Growth rate = increase ÷ initial number ÷ time (e.g. 200/1000/5 = 0.04 per year, 4%).

  ✓Do this: Write the formula in words before substituting.

  Usually costs: 1 mark.

Practice questions on Biodiversity and its Conservation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which is an example of in-situ conservation?
   (a) seed bank
   (b) zoo
   (c) national park
   (d) cryopreservation

   Hint

   Natural habitat.

   Answer

   (c)

2. Q2 · 1 mark · MCQBoard level

   The Nile perch caused extinction of cichlid fish in:
   (a) Lake Tanganyika
   (b) Lake Victoria
   (c) Lake Baikal
   (d) Chilika Lake

   Hint

   Africa.

   Answer

   (b)

3. Q3 · 1 mark · Very short answerBoard level

   Name the scientist who proposed the rivet popper hypothesis.

   Hint

   Stanford ecologist.

   Answer

   Paul Ehrlich

4. Q4 · 1 mark · Very short answerBoard level

   Where and when was the Ramsar Convention signed?

   Hint

   Wetlands.

   Answer

   Ramsar, Iran, 1971.

5. Q5 · 1 mark · Very short answerBoard level

   Name four recently extinct animals.

   Hint

   Mauritius, Africa, Australia, Russia.

   Answer

   Dodo, quagga, thylacine, Steller's sea cow (also Bali, Javan and Caspian tigers).

6. Q6 · 2 marks · Short answerHarder board level

   If doubling the area of a region with Z = 0.2 is planned for a reserve, by what factor will species richness increase?

   Hint

   2^0.2.

   Answer

   2^0.2 = 1.15: about 15% more species.

7. Q7 · 2 marks · Short answerHarder board level

   The number of species in an ecosystem rose from 800 to 960 over 4 years. Calculate the average annual growth rate of species number.

   Hint

   Increase / initial / time.

   Answer

   Increase 160; 160/800 = 0.2 over 4 years = 0.05 per year (5%).

8. Q8 · 2 marks · Short answerHarder board level

   Explain how habitat fragmentation affects large mammals and migratory birds.

   Hint

   Territory size.

   Answer

   Large habitats broken into small patches cannot support animals that need large territories (tigers, elephants), and barriers disrupt migration routes, leading to population declines.

9. Q9 · 2 marks · Short answerBoard level

   Give two features each of national parks and sacred groves.

   Hint

   Legal vs traditional.

   Answer

   National parks: government-protected, no grazing or cultivation, e.g. Jim Corbett. Sacred groves: protected by communities for religious reasons, all trees and wildlife venerated, e.g. Khasi and Jaintia Hills.

10. Q10 · 2 marks · Short answerHarder board level

    Explain how cryopreservation and tissue culture help conserve biodiversity.

    Hint

    −196 °C.

    Answer

    Cryopreservation stores gametes, embryos or tissues in liquid nitrogen (−196 °C) in viable condition for long periods; tissue culture regenerates many plants from small pieces of threatened species.

11. Q11 · 5 marks · Long answerHarder board level

    (a) Describe genetic, species and ecological diversity with examples. [3]
    (b) What is the World Summit on Sustainable Development? [2]

    Hint

    Rauwolfia; Johannesburg.

    Answer

    (a) Genetic: variation within a species (Rauwolfia vomitoria reserpine levels; 50 000 rice strains). Species: number of species in a region (Western Ghats amphibians > Eastern Ghats). Ecological: variety of ecosystems (India's deserts, rainforests, mangroves, coral reefs, alpine meadows). (b) Held in Johannesburg, South Africa, in 2002; 190 countries pledged to achieve a significant reduction in the rate of biodiversity loss by 2010.

12. Q12 · 2 marks · Short answerHOTS / competency

    Tilman's plots with more species showed less year-to-year variation in biomass. Relate this to the rivet popper hypothesis.

    Hint

    Stability.

    Answer

    More species (rivets) make the ecosystem (plane) more stable and productive; losing species reduces stability, just as popping rivets weakens the plane.

13. Q13 · 2 marks · Short answerHOTS / competency

    Why may the loss of a single keystone species cause greater harm than the loss of several other species?

    Hint

    Wing rivets.

    Answer

    A keystone species drives major ecosystem functions (like wing rivets); its loss can collapse food webs and cause co-extinctions, while many other species may have redundant roles.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Who popularised the term biodiversity?Show answer

   Edward Wilson.

2. 2.Approximate number of species estimated by Robert May?Show answer

   About 7 million.

3. 3.India's share of global species diversity?Show answer

   About 8.1%.

4. 4.Equation of the species-area relationship?Show answer

   $\log S=\log C+Z\log A$ (S = CA^Z).

5. 5.What is endemism?Show answer

   Species confined to a particular region and found nowhere else.

6. 6.Name an Indian Ramsar site.Show answer

   Chilika Lake (or Keoladeo, Loktak, Wular).

7. 7.Which organisation maintains the Red List?Show answer

   IUCN.

8. 8.Where was the World Summit 2002 held?Show answer

   Johannesburg, South Africa.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you give examples of genetic, species and ecological diversity?
• ☐Can you state three reasons why tropics are richer?
• ☐Can you calculate S = CA^Z and compare regions?
• ☐Can you explain the rivet popper hypothesis completely?
• ☐Can you distinguish narrowly and broadly utilitarian arguments?
• ☐Can you name recent extinctions and the evil quartet with examples?
• ☐Can you distinguish national park, sanctuary, biosphere reserve and sacred grove?
• ☐Can you state the place, year and agenda of the Earth Summit and World Summit?

Biodiversity and its Conservation: frequently asked questions