Section 12 — Board Exam-Pattern Questions (Class 12 Biology, Chapter 13)
Chapter 13 (Biodiversity and Conservation) is one of the most dependable scoring chapters in the Class 12 Biology Board paper. Its parent unit (Ecology and Environment, about 10 marks) leans on it every year — questions spread across MCQs, 2/3-mark short answers, and very often a 5-mark question on patterns of diversity, causes of loss, or conservation strategies.
This section curates 24 high-yield Board exam-pattern questions (modelled on the CBSE style — not year-tagged official questions) in the mark-wise format used in Board papers:
| Marks | Number of Qs | Indicative frequency in papers |
|---|---|---|
| 1 mark | 7 questions (Q1–Q7) | 2–3 / paper |
| 2 marks | 6 questions (Q8–Q13) | 2 / paper |
| 3 marks | 6 questions (Q14–Q19) | 1–2 / paper |
| 5 marks | 5 questions (Q20–Q24) | 1 / paper (very high probability) |
| Total | 24 questions | 62 marks of practice |
How to use: Cover the answer, attempt it yourself scaled to the marks, then check against the model answer and its keyword notes.
No quiz at the end: Pair this set with the Solved Examples and the NEET practice sections.
What the Board Keeps Asking
Most questions on Chapter 13 fall into six recurring themes:
1. Levels and measures of biodiversity (1- or 2-mark) — genetic, species and ecological diversity; identify-the-level scenarios; the mega diversity status of India.
2. How many species and global patterns (1- or 2-mark) — Robert May's estimate, proportion of insects and fungi, India's share.
3. Patterns of diversity (2-, 3- or 5-mark) — the latitudinal gradient and its three hypotheses, the species-area relationship and the meaning of the slope.
4. Importance and loss (2-, 3- or 5-mark) — the rivet popper hypothesis, Tilman's experiments, the Sixth Extinction, and the Evil Quartet.
5. Why conserve (2- or 3-mark) — narrowly utilitarian, broadly utilitarian and ethical arguments.
6. Conservation strategies (3- or 5-mark) — in-situ methods (hotspots, biosphere reserves, national parks, sanctuaries, sacred groves) and ex-situ methods (zoos, seed banks, cryopreservation).
1-Mark Questions (Q1–Q7)
Q1. [1 mark] Name the three most important levels at which biodiversity exists.
Answer: Genetic diversity, species diversity and ecological (ecosystem) diversity.
Keyword note: all three levels are needed for the full mark.
Q2. [1 mark] What is the name given collectively to the four major causes of biodiversity loss?
Answer: The Evil Quartet.
Q3. [1 mark] Write the species-area relationship on a logarithmic scale.
Answer: where S is species richness, A is area, Z is the slope and C is the Y-intercept.
Q4. [1 mark] How many biodiversity hotspots are currently recognised in the world, and how many lie in India?
Answer: 34 hotspots in the world; three of them extend into India (Western Ghats and Sri Lanka, Indo-Burma, Himalaya).
Q5. [1 mark, Assertion-Reason]
Assertion (A): India is regarded as a mega diversity country. Reason (R): India has 2.4 per cent of the world's land area but 8.1 per cent of the global species diversity.
Options: (a) Both A and R true and R explains A. (b) Both true but R does not explain A. (c) A true, R false. (d) A false, R true.
Answer: (a) — India's disproportionately high species share on a small land area is exactly why it counts among the 12 mega diversity countries, so R correctly explains A.
Q6. [1 mark] Name the conservation approach in which a threatened species is taken out of its natural habitat and cared for in a special setting.
Answer: Ex-situ (off-site) conservation.
Q7. [1 mark] According to Robert May, what is the estimated true number of species on Earth?
Answer: About 7 million species.
2-Mark Questions (Q8–Q13)
Q8. [2 marks] Distinguish between genetic diversity and species diversity, giving one example of each.
Answer: Genetic diversity is variation within a single species across its range, e.g. the 50,000 strains of rice or Rauwolfia vomitoria differing in reserpine content. Species diversity is diversity measured as the number of species in a region, e.g. the Western Ghats having more amphibian species than the Eastern Ghats.
Keyword note: within-species versus number-of-species is the marking axis.
Q9. [2 marks] State any two hypotheses proposed to explain the greater species richness of the tropics.
Answer: (i) The tropics have had a long, undisturbed evolutionary time for diversification, unlike temperate regions hit by repeated glaciations. (ii) Tropical environments are less seasonal and more constant, promoting niche specialisation. (A third accepted point: the tropics receive more solar energy, raising productivity.)
Q10. [2 marks] What does the slope Z of the species-area line signify, and what values does it take within a region and across continents?
Answer: Z (the regression coefficient) measures how fast species richness rises with area. Within a region it is remarkably constant at 0.1 to 0.2, but across very large areas such as whole continents the slope is much steeper, 0.6 to 1.2.
Q11. [2 marks] What are sacred groves, and what is their role in conservation?
Answer: Sacred groves are tracts of forest set aside and given total protection because of religious and cultural traditions. They act as in-situ refuges; in Meghalaya they are the last refuges for many rare and threatened plants.
Q12. [2 marks] Distinguish between in-situ and ex-situ conservation.
Answer: In in-situ conservation a species is protected inside its natural habitat by conserving the whole ecosystem (biosphere reserves, national parks, sanctuaries, sacred groves). In ex-situ conservation the species is taken out of its habitat and maintained in a special setting (zoos, botanical gardens, seed banks, cryopreservation).
Q13. [2 marks] Explain the rivet popper hypothesis and name the ecologist associated with it.
Answer: Proposed by Paul Ehrlich, the hypothesis likens an ecosystem to an aeroplane and each species to a rivet holding it together. Removing a few rivets (species) may not harm flight safety at first, but continued loss weakens the plane dangerously, and losing rivets on the wings (key species) is far more damaging than losing those on the seats.
3-Mark Questions (Q14–Q19)
Q14. [3 marks] Describe the latitudinal gradient in species diversity and give the three hypotheses proposed to explain the richness of the tropics.
Answer: Species diversity generally decreases from the equator towards the poles; the tropics (23.5 degrees N to 23.5 degrees S) harbour more species than temperate or polar regions, e.g. Colombia has nearly 1,400 bird species against Greenland's 56. The three hypotheses are: (i) tropics had a long, undisturbed evolutionary time; (ii) their environment is constant and less seasonal, favouring niche specialisation; (iii) they receive more solar energy, raising productivity and indirectly supporting more species.
Keyword note: equator-to-pole decrease plus the three named hypotheses.
Q15. [3 marks] Name and briefly explain any three members of the Evil Quartet responsible for biodiversity loss.
Answer: (i) Habitat loss and fragmentation — the most important cause; tropical rainforests are cleared and large habitats broken into fragments, hurting wide-ranging and migratory animals. (ii) Over-exploitation — when need turns to greed, resources are harvested to extinction, as with the passenger pigeon and Steller's sea cow. (iii) Alien species invasions — introduced species turn invasive, e.g. the Nile perch eliminating over 200 cichlid species in Lake Victoria. (A fourth: co-extinctions, where losing one species drags down its obligate associates.)
Q16. [3 marks] What is the species-area relationship? Draw out its equation and explain the meaning of the slope for small and very large areas.
Answer: Alexander von Humboldt observed that within a region species richness rises with area up to a limit, tracing a rectangular hyperbola. On a log scale it becomes the straight line where S is species richness, A is area, Z is the slope and C the intercept. For analyses within a region Z stays at 0.1 to 0.2 regardless of taxon; across whole continents the slope steepens to 0.6 to 1.2 because separate continents hold their own distinct evolutionary lineages.
Q17. [3 marks] How is the Sixth Extinction different from the earlier mass extinctions, and what are its likely consequences?
Answer: Earth's fossil record shows five earlier mass extinctions before humans appeared. The Sixth Extinction, now in progress, differs in its rate — present extinction rates are 100 to 1,000 times faster than pre-human times, driven by human activity. If current trends continue, ecologists warn that nearly half of all species could vanish within the next 100 years, with declines in plant production and lowered resistance to disturbances such as drought.
Q18. [3 marks] Give the narrowly utilitarian, broadly utilitarian and ethical arguments for conserving biodiversity.
Answer: Narrowly utilitarian — direct economic benefits such as food, firewood, fibre, industrial products and medicines (over 25 per cent of drugs sold worldwide come from plants). Broadly utilitarian — ecosystem services such as the oxygen produced by forests (the Amazon yields about 20 per cent of atmospheric oxygen) and pollination by bees, birds and bats. Ethical — every species has an intrinsic value and we have a moral duty to pass on our biological legacy to future generations.
Q19. [3 marks] Describe any three modern ex-situ conservation techniques used for threatened species.
Answer: (i) Cryopreservation — gametes of threatened species are frozen in viable, fertile condition for long periods. (ii) In-vitro fertilisation — eggs are fertilised in the laboratory to raise offspring outside the body. (iii) Tissue culture and seed banks — plants are propagated by tissue culture, and seeds of different genetic strains of commercially important plants are stored for long periods in seed banks.
5-Mark Questions (Q20–Q24)
Q20. [5 marks] Explain the patterns of biodiversity under two heads: the latitudinal gradient and the species-area relationship. Include the equation and the meaning of its slope.
Answer:
Latitudinal gradient: Species diversity is not uniform; it generally decreases from the equator towards the poles. The tropics harbour more species than temperate or polar areas — Colombia near the equator has about 1,400 bird species, New York 105 and Greenland only 56. The Amazonian rainforest has the greatest biodiversity on Earth. Three hypotheses explain tropical richness: long undisturbed evolutionary time, a constant, less seasonal environment favouring niche specialisation, and greater solar energy raising productivity.
Species-area relationship: Within a region, species richness rises with area up to a limit, giving a rectangular hyperbola. On a log scale this is the straight line
where S is species richness, A is area, Z is the slope and C the Y-intercept. The slope Z is 0.1 to 0.2 within a region, but steepens to 0.6 to 1.2 across whole continents.
Keyword note: equator-to-pole decrease, three hypotheses, the log equation, and the two Z ranges.
Q21. [5 marks] Human activities are driving an accelerated loss of biodiversity. Describe the four major causes grouped under the Evil Quartet, with one example each.
Answer:
(i) Habitat loss and fragmentation — the single most important cause. Tropical rainforests, once over 14 per cent of the land surface, now cover no more than 6 per cent, cleared for soya bean and cattle; fragmentation of large habitats badly affects wide-ranging mammals, birds and migratory species.
(ii) Over-exploitation — when need turns to greed, resources are harvested beyond recovery, as with the extinct passenger pigeon and Steller's sea cow, and today's over-harvested marine fisheries.
(iii) Alien species invasions — introduced species turn invasive and eliminate natives, e.g. the Nile perch wiping out more than 200 cichlid species in Lake Victoria, and Indian weeds such as Parthenium, Lantana and water hyacinth.
(iv) Co-extinctions — when a species is lost, its obligate associates follow, as when an obligate parasite dies with its host, or one partner of a plant-pollinator mutualism is lost.
Q22. [5 marks] Why should biodiversity be conserved? Explain the reasons and support the broadly utilitarian argument with specific ecosystem services.
Answer:
The reasons fall into three groups. Narrowly utilitarian arguments cover the direct economic products humans draw from nature — food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, dyes, resins, perfumes) and medicines; more than 25 per cent of drugs sold worldwide are plant-derived, and bioprospecting promises still more.
The broadly utilitarian argument rests on ecosystem services: the Amazon forest produces roughly 20 per cent of the atmosphere's oxygen through photosynthesis; pollination by bees, bumblebees, birds and bats lets plants set fruit and seed; and there are intangible aesthetic benefits such as watching spring flowers or waking to birdsong.
The ethical argument holds that every species has an intrinsic value regardless of its economic worth, and that we have a moral duty to care for all life and hand on our biological legacy in good order to future generations.
Q23. [5 marks] Compare in-situ and ex-situ conservation. Describe India's in-situ network and the concept of biodiversity hotspots.
Answer:
In-situ conservation protects a species within its natural habitat by conserving the whole ecosystem — we save the entire forest to save the tiger. Ex-situ conservation takes a threatened species out of its habitat into zoos, botanical gardens, safari parks, seed banks and cryopreservation facilities when urgent rescue is needed.
Biodiversity hotspots are regions of very high species richness and endemism that are also under accelerated habitat loss. There are 34 worldwide; though together they cover less than 2 per cent of the land, strict protection could cut ongoing mass extinctions by nearly 30 per cent. Three of them extend into India — Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.
India's in-situ network includes 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries, together with sacred groves in Meghalaya, the Aravalli Hills and the Western Ghats that give traditional total protection to forest tracts.
Q24. [5 marks] Discuss the importance of species diversity to ecosystem functioning, referring to community stability, Tilman's experiments and the rivet popper hypothesis, and note the global efforts to conserve biodiversity.
Answer:
Species richness and stability: Communities with more species tend to be more stable — a stable community shows little year-to-year variation in productivity, resists or recovers from disturbances, and resists invasion by alien species.
Tilman's experiments: David Tilman's long-term outdoor plots showed that plots with more species had less year-to-year variation in biomass and that increased diversity raised productivity, giving experimental support to the link between richness and ecosystem health.
Rivet popper hypothesis: Paul Ehrlich compared the ecosystem to an aeroplane held together by rivets (species). Losing a few rivets may not harm flight safety at first, but continued loss weakens the plane, and losing rivets on the wings (key species) is far more serious than losing those on the seats.
Global efforts: The Convention on Biological Diversity (the Earth Summit), Rio de Janeiro 1992, urged all nations to conserve biodiversity and use its benefits sustainably; the 2002 Johannesburg summit saw 190 countries pledge to reduce the rate of biodiversity loss.
End of Section 12
You have now worked through 24 high-yield Board questions spanning the levels and measures of biodiversity, the latitudinal and species-area patterns, the importance of diversity to ecosystems, the causes of loss, and both conservation strategies. If you can answer the five 5-markers (Q20–Q24) from memory with their key points, you have effectively secured this chapter's contribution to your paper.
Final tip: In pattern questions always write the equation with the two Z ranges, and in loss questions always name the specific member of the Evil Quartet. Tabulate comparison answers (genetic vs species, in-situ vs ex-situ) for quick, full-mark responses.