Section 11 — Solved Examples
This is the dedicated problem set for Chapter 13 (Biodiversity and Conservation). The 30 worked examples below are arranged in three tiers — concept checks (levels of diversity, key numbers, definitions), application and scenarios (identify-the-level, identify-the-cause, in-situ versus ex-situ decisions), and analytical and multi-concept (reasoning problems that connect patterns, loss and conservation across the whole chapter).
Most of these ask you to identify, classify and justify, because that is exactly how a biodiversity question earns marks in a Board or NEET paper. Naming a figure is rarely enough; you are usually asked which level of diversity is shown, which cause of loss is at work, or why the tropics are so rich.
How to use this section
- Concept Checks (Q1–Q10): Quick recall of levels, numbers, patterns and terms. If you stumble on more than one or two, revisit Sections 1–5.
- Application and Scenarios (Q11–Q20): The workhorse 2- and 3-mark items — classify the level of diversity, name the member of the Evil Quartet, choose in-situ or ex-situ.
- Analytical and Multi-Concept (Q21–Q30): Multi-step reasoning that ties several topics together, including a full working of the species-area equation.
Total target time: around an hour for a complete revision sweep.
Note: This section is for practice and revision only — there is no quiz at the end. Treat each answer as a model of how much detail an examiner expects.
Memory Capsule — Facts Worth Locking In
Before working through the problems, fix these ten high-yield facts firmly in mind:
| # | Fact | Where it is tested |
|---|---|---|
| 1 | Three levels of biodiversity — genetic, species, ecological; the term was popularised by Edward Wilson | Identify-the-level |
| 2 | Global species described so far by IUCN is slightly over 1.5 million; Robert May estimates the true total near 7 million | Numbers |
| 3 | More than 70 per cent of recorded species are animals; of these, insects make up more than 70 per cent; fungi outnumber fishes, amphibians, reptiles and mammals combined | Proportion questions |
| 4 | India has 2.4 per cent of the land area but 8.1 per cent of global species — one of 12 mega diversity countries | India figures |
| 5 | Species diversity falls from the equator to the poles; three reasons — more evolutionary time, constant environment, more solar energy | Latitudinal gradient |
| 6 | Species-area relation is a rectangular hyperbola; on a log scale it is linear; slope Z is 0.1–0.2 for small areas, 0.6–1.2 across continents | Equation questions |
| 7 | The rivet popper hypothesis (Paul Ehrlich) and Tilman's plot experiments argue that richer communities are more stable and productive | Ecosystem role |
| 8 | The Evil Quartet — habitat loss and fragmentation, over-exploitation, alien species invasions, co-extinctions | Identify-the-cause |
| 9 | Reasons to conserve — narrowly utilitarian, broadly utilitarian, ethical | Why conserve |
| 10 | In-situ — hotspots (34 total; 3 in India), biosphere reserves, national parks, sanctuaries, sacred groves; ex-situ — zoos, botanical gardens, seed banks, cryopreservation, in-vitro fertilisation | In-situ vs ex-situ |
Pro tip: For a classify question, first ask what is varying — genes within one species, species within a region, or whole ecosystems. For a loss question, always pin the scenario to one named member of the Evil Quartet.
Concept Checks (Q1–Q10)
Q1. Name the three most important levels of biodiversity and state who popularised the term.
Answer: The three levels are genetic diversity, species diversity and ecological (ecosystem) diversity. The term biodiversity was popularised by the sociobiologist Edward Wilson to describe the combined diversity at all levels of biological organisation, from macromolecules within cells to whole biomes.
Q2. How many species have been described so far, and what is Robert May's estimate of the true global total?
Answer: According to IUCN, the number of plant and animal species described so far is slightly more than 1.5 million. A conservative and scientifically sound estimate by Robert May places the true global species diversity at about 7 million, which means only around 22 per cent of the total has been recorded.
Q3. Among all recorded species, which group is the most species-rich, and how do fungi compare with vertebrates?
Answer: More than 70 per cent of recorded species are animals, and among animals the insects are the most species-rich group, making up more than 70 per cent — so 7 out of every 10 animals is an insect. The number of fungal species is more than the combined total of fishes, amphibians, reptiles and mammals.
Q4. Why is India called a mega diversity country? Support your answer with figures.
Answer: Although India has only 2.4 per cent of the world's land area, its share of global species diversity is 8.1 per cent, which makes it one of the 12 mega diversity countries of the world. Nearly 45,000 species of plants and twice as many animals have been recorded here.
Q5. State the latitudinal gradient in diversity and give one supporting example.
Answer: Species diversity generally decreases as we move away from the equator towards the poles; with very few exceptions, the tropics harbour more species than temperate or polar areas. For example, Colombia near the equator has nearly 1,400 species of birds, while New York at 41 degrees N has 105 and Greenland at 71 degrees N only 56.
Q6. Which region on Earth has the greatest biodiversity, and what is it often called?
Answer: The largely tropical Amazonian rainforest in South America has the greatest biodiversity on Earth. Because of the oxygen it releases, it is often called the lungs of the planet. It is home to more than 40,000 plant species, 3,000 fishes, 1,300 birds and vast numbers of invertebrates.
Q7. Name the four members of the Evil Quartet.
Answer: The four major causes of biodiversity loss, collectively called the Evil Quartet, are habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions. Of these, habitat loss and fragmentation is the single most important driver of extinctions.
Q8. What is a biodiversity hotspot, and how many are recognised worldwide?
Answer: A biodiversity hotspot is a region with very high species richness and a high degree of endemism (species confined to that region), which is also facing accelerated habitat loss. Initially 25 were identified; nine more were later added, bringing the world total to 34.
Q9. Define in-situ and ex-situ conservation in one line each.
Answer: In-situ (on-site) conservation protects a species inside its own natural habitat by protecting the whole ecosystem — we save the entire forest to save the tiger. Ex-situ (off-site) conservation takes a threatened species out of its habitat and cares for it in a special setting such as a zoo, botanical garden or seed bank.
Q10. Under which three headings are the reasons for conserving biodiversity grouped?
Answer: The reasons are grouped as narrowly utilitarian (direct economic products such as food, firewood, fibre and medicines), broadly utilitarian (ecosystem services such as oxygen release and pollination) and ethical (the moral duty we owe to every species that shares the planet).
Application and Scenarios (Q11–Q20)
Q11. India has more than 50,000 genetically different strains of rice and about 1,000 varieties of mango. Which level of biodiversity does this illustrate, and why?
Answer: This illustrates genetic diversity, because the variation is within a single species (rice, or mango). All 50,000 rice strains are the same species yet differ genetically, exactly as Rauwolfia vomitoria growing in different Himalayan ranges differs in the potency and concentration of its reserpine.
Q12. The Western Ghats have more amphibian species than the Eastern Ghats. Identify the level of diversity shown.
Answer: This is species diversity — diversity measured as the number of different species in a region. The comparison is between two regions on the count of amphibian species, not on genes within one species or on the number of ecosystem types, so it is species-level diversity.
Q13. India has deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows, far more than a country like Norway. Which level of diversity is this?
Answer: This is ecological (ecosystem) diversity, because what varies is the number and kinds of ecosystems. India's wide range of ecosystem types gives it a greater ecological diversity than a Scandinavian country such as Norway.
Q14. The Nile perch was introduced into Lake Victoria and wiped out more than 200 species of native cichlid fish. Which member of the Evil Quartet is responsible?
Answer: This is alien species invasion. An introduced (alien) species turned invasive and caused the decline and extinction of indigenous species. Other Indian examples of the same cause are the weeds Parthenium (carrot grass), Lantana and water hyacinth (Eichhornia), and the illegally introduced African catfish Clarias gariepinus.
Q15. Tropical rainforests once covered more than 14 per cent of the land surface but now cover no more than 6 per cent, largely cleared for soya bean and cattle. Name the cause of biodiversity loss at work.
Answer: This is habitat loss and fragmentation, the most important cause of extinctions. Clearing the Amazon for cultivation destroys habitat outright, and when large habitats are broken into small fragments, mammals and birds needing large territories and migratory animals are badly affected, leading to population declines.
Q16. When a host fish species becomes extinct, its unique assemblage of parasites also disappears, and when one partner of a plant-pollinator pair is lost the other soon follows. Which member of the Evil Quartet does this describe?
Answer: This describes co-extinctions. When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct, as with an obligate parasite losing its host, or a coevolved plant-pollinator mutualism where the loss of one drives the extinction of the other.
Q17. A rare Himalayan medicinal plant is critically endangered in the wild. Wildlife managers cannot yet secure its habitat but want to save it immediately. Should they choose in-situ or ex-situ conservation, and how?
Answer: With the habitat not yet secured and the species facing a very high risk of extinction, ex-situ conservation is the desirable approach here. The plant can be grown and protected in a botanical garden, propagated by tissue culture, and its seeds of different genetic strains stored in a seed bank, so the species is preserved even while its wild habitat remains unprotected.
Q18. To protect the tiger, planners decide to protect the entire forest it lives in rather than move it to a zoo. Name and justify this conservation strategy.
Answer: This is in-situ (on-site) conservation. By conserving and protecting the whole ecosystem, biodiversity at all levels is protected at once — we save the entire forest to save the tiger. In India this is done through biosphere reserves, national parks and wildlife sanctuaries, which shield the tiger together with every other species sharing its habitat.
Q19. Gametes of a threatened deer are frozen for future use, its eggs are fertilised in the laboratory, and seeds of a crop's wild relatives are stored. Which broad approach do these techniques belong to, and name them.
Answer: These are all ex-situ conservation techniques. They include cryopreservation of gametes in viable and fertile condition, in-vitro fertilisation of eggs, tissue culture propagation of plants, and storage of different genetic strains in seed banks — modern methods that go beyond simply keeping animals in enclosures.
Q20. Sacred groves are found in the Khasi and Jaintia Hills of Meghalaya, the Aravalli Hills and parts of the Western Ghats. What are they, and how do they help conservation?
Answer: Sacred groves are tracts of forest set aside and given total protection because of religious and cultural traditions, where all trees and wildlife are venerated. They act as a form of in-situ conservation; in Meghalaya they are the last refuges for a large number of rare and threatened plants, preserving them without any formal legal machinery.
Analytical and Multi-Concept (Q21–Q30)
Q21. On a logarithmic scale the species-area relationship becomes a straight line. Write the equation, state what each symbol means, and explain why a log plot is preferred.
Answer: On a log scale the relationship is a straight line described by
where S is species richness, A is area, Z is the slope of the line (the regression coefficient) and C is the Y-intercept. On ordinary axes the relation is a rectangular hyperbola, which is awkward to read; taking logarithms straightens it into a line whose slope Z can be measured directly and compared across taxa and regions.
Q22. In a study, the species-area line for plants in a region has C equal to 100 and Z equal to 0.2. Estimate the species richness for an area of 10,000 units using the log equation.
Answer: Substitute into the equation with logarithms to base 10. Here and , so
gives . Taking the antilog, , which is about 631 species. The working shows how the equation converts an area into an expected species count once C and Z are known.
Q23. Ecologists find Z near 0.15 for molluscs within one region but about 1.15 for frugivorous birds across continents. Explain what the slope tells us and why the second value is so much steeper.
Answer: The slope Z measures how fast species richness rises with area. For analyses within a region the value is remarkably constant at 0.1 to 0.2, regardless of taxon or place. But across very large areas such as whole continents the slope becomes much steeper, 0.6 to 1.2, because separate continents have accumulated their own distinct evolutionary lineages, so adding continental-scale area adds far more new species than adding area within a single region.
Q24. Three hypotheses explain why the tropics are so species-rich. State them, and identify which one rests on the absence of past glaciations.
Answer: The three hypotheses are: (a) the tropics have had a long, undisturbed evolutionary time for diversification, unlike temperate regions repeatedly hit by glaciations; (b) tropical environments are less seasonal and more constant, which promotes niche specialisation and greater species diversity; and (c) the tropics receive more solar energy, raising productivity and indirectly supporting more species. The hypothesis resting on the absence of past glaciations is (a), the evolutionary time argument.
Q25. Using the rivet popper analogy, explain why losing some species may be tolerated at first but why the identity of the species lost still matters.
Answer: In Paul Ehrlich's rivet popper hypothesis the ecosystem is an aeroplane and each species a rivet holding it together. Popping a few rivets may not affect flight safety at first, but as more are removed the plane grows dangerously weak — so early species loss may not visibly harm ecosystem function, yet continued loss eventually threatens it. The identity matters because rivets on the wings (key species driving major ecosystem functions) are far more critical than rivets on the seats, so losing a key species is far more damaging than losing a minor one.
Q26. David Tilman's long-term plot experiments are often quoted in this chapter. What two findings did they yield, and what do they suggest about species richness?
Answer: Tilman's outdoor plot experiments showed that plots with more species had less year-to-year variation in total biomass, and that increased diversity led to higher productivity. Together these findings support the long-held view that communities with more species tend to be more stable and more productive, giving experimental weight to the idea that rich biodiversity underpins healthy ecosystem functioning.
Q27. The current wave of extinction is called the Sixth Extinction. How does it differ from the five earlier mass extinctions, and what evidence points the finger at humans?
Answer: Earth's fossil record shows five earlier episodes of mass extinction that occurred before humans appeared. The Sixth Extinction differs in its rate — present extinction rates are estimated to be 100 to 1,000 times faster than in pre-human times, and this acceleration coincides with human activities. Ecologists warn that if current trends continue, nearly half of all species could be wiped out within the next 100 years.
Q28. Both the passenger pigeon and Steller's sea cow vanished within the last 500 years for the same reason, while the dodo and the quagga are named simply as recent extinctions. Which cause drove the first pair, and what general lesson does the marine example teach today?
Answer: The passenger pigeon and Steller's sea cow were lost through over-exploitation by humans — when need turns to greed, natural resources are harvested beyond recovery. The lesson carries into the present because many marine fish populations are now over-harvested, endangering the continued existence of commercially important species, exactly the same cause acting in a modern setting.
Q29. A politician argues that saving the Amazon rainforest brings no cash return. Using narrowly utilitarian, broadly utilitarian and ethical arguments, rebut this claim.
Answer: Narrowly utilitarian: the forest yields direct products — food, firewood, fibre, industrial materials and medicines; more than 25 per cent of drugs sold worldwide come from plants, so bioprospecting alone promises large returns. Broadly utilitarian: the Amazon provides ecosystem services, producing about 20 per cent of the atmosphere's oxygen through photosynthesis and supporting pollination, whose replacement cost would be enormous. Ethical: every species has an intrinsic value and we have a moral duty to hand on our biological legacy in good order to future generations. On all three counts the claim fails.
Q30. Explain how in-situ and ex-situ conservation work together, naming India's in-situ network and at least two modern ex-situ techniques, and identify the 1992 summit that made conservation a global commitment.
Answer: In-situ conservation protects species in their natural habitats and forms the first line of defence — India maintains 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries, plus sacred groves and shares in three global hotspots (Western Ghats and Sri Lanka, Indo-Burma, Himalaya). Ex-situ conservation rescues species that cannot yet be saved in the wild, through zoos, botanical gardens, seed banks, cryopreservation of gametes and in-vitro fertilisation. The two are complementary. Conservation became a global commitment at the Convention on Biological Diversity, the Earth Summit held in Rio de Janeiro in 1992, reinforced by the 2002 Johannesburg summit.
End of Section 11
You have now worked through 30 examples spanning the three levels of diversity, the key global and Indian figures, latitudinal gradients, the species-area equation and its slope, the importance of diversity to the ecosystem, extinctions and the Evil Quartet, the three arguments for conservation, and in-situ versus ex-situ strategies. For every question, keep two habits — first classify what is varying to fix the level of diversity, then pin any loss scenario to a named member of the Evil Quartet, and you will rarely leave marks on the table.