NCERT Solutions for Class 12 Biology Chapter 13: Biodiversity and Conservation (NCERT 2026–27)
These Class 12 Biology Chapter 13 solutions cover Biodiversity and Conservation from the NCERT textbook (2026–27). You get every end-of-chapter NCERT exercise reproduced verbatim and answered in exam-ready prose, plus key concepts, extra practice, MCQs and Assertion–Reason questions on genetic, species and ecological diversity, latitudinal gradients, the species–area relationship, the ‘Evil Quartet’, biodiversity hotspots and in situ/ex situ conservation.
Chapter 13, Biodiversity and Conservation, studies the variety of life on Earth and how we protect it. Biodiversity — a term popularised by Edward Wilson — is the combined diversity at all levels of biological organisation, the three most important being genetic, species and ecological diversity. The chapter looks at how many species exist (about 1.5 million recorded; an estimated 7 million by Robert May), India’s status as one of 12 mega-diversity nations, and the global patterns of biodiversity — the latitudinal gradient (richest in the tropics) and the species–area relationship (a rectangular hyperbola, log S = log C + Z log A). It then covers the loss of biodiversity through the ‘Evil Quartet’ and the three reasons (narrowly utilitarian, broadly utilitarian, ethical) for conservation, ending with in situ methods (hotspots, biosphere reserves, national parks, sanctuaries, sacred groves) and ex situ methods (zoos, botanical gardens, cryopreservation, seed banks).
Key Concepts & Definitions
Biodiversity: the sum total of diversity that exists at all levels of biological organisation, from macromolecules to biomes.
Genetic diversity: diversity within a single species over its range, e.g. Rauwolfia vomitoria producing different concentrations of reserpine; India has >50,000 strains of rice and 1,000 mango varieties.
Species diversity: diversity at the species level, e.g. greater amphibian diversity in the Western Ghats than the Eastern Ghats.
Ecological diversity: diversity at the ecosystem level, e.g. India (deserts, rainforests, mangroves, coral reefs, wetlands, alpine meadows) versus Norway.
Latitudinal gradient: species diversity generally decreases from the equator (tropics, 23.5° N–23.5° S) towards the poles.
Species–area relationship: within a region species richness rises with area as a rectangular hyperbola; on a log scale it is the straight line log S = log C + Z log A, where Z (slope) is 0.1–0.2 for small areas and 0.6–1.2 across continents.
The Evil Quartet: the four causes of biodiversity loss — habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinctions.
In situ conservation: protecting species in their natural habitat (hotspots, biosphere reserves, national parks, sanctuaries, sacred groves).
Ex situ conservation: protecting species outside their habitat (zoological parks, botanical gardens, cryopreservation of gametes, in vitro fertilisation, tissue culture, seed banks).
NCERT Exercises — Solutions
All questions below are reproduced verbatim from the NCERT textbook (Reprint 2026–27). Answers are original and written in CBSE exam-ready style.
1. Name the three important components of biodiversity.
ANSWERThe three important components (levels) of biodiversity are:(i) Genetic diversity – the variation in genes within a single species over its distributional range (e.g. India’s >50,000 strains of rice and 1,000 varieties of mango; varying reserpine levels in Rauwolfia vomitoria).(ii) Species diversity – the diversity at the level of species (e.g. the Western Ghats have greater amphibian diversity than the Eastern Ghats).(iii) Ecological (ecosystem) diversity – the diversity at the ecosystem level (e.g. India, with deserts, rainforests, mangroves, coral reefs, wetlands and alpine meadows, has greater ecosystem diversity than Norway).
2. How do ecologists estimate the total number of species present in the world?
ANSWERSince only about 1.5 million species have actually been recorded and the vast majority of undiscovered species lie in the poorly explored tropics, ecologists rely on statistical extrapolation rather than direct counting.They take a taxonomic group that has been studied exhaustively (for example, certain insects) and work out the ratio of temperate to tropical species richness for that group. This known ratio is then applied (extrapolated) to other groups of animals and plants whose tropical diversity is still poorly known.By combining such estimates across groups they arrive at a gross figure for the total number of species on Earth. Estimates range widely (20–50 million), but Robert May’s more conservative and scientifically sound estimate places global species diversity at about 7 million.
3. Give three hypotheses for explaining why tropics show greatest levels of species richness.
ANSWER(a) More evolutionary time: Speciation is generally a function of time. Unlike temperate regions, which faced frequent glaciations, tropical latitudes have remained relatively undisturbed for millions of years, giving species a long uninterrupted period for diversification.(b) Constant, less seasonal environment: Tropical environments are less seasonal and more constant and predictable. Such stable conditions promote niche specialisation, which leads to greater species diversity.(c) More solar energy/productivity: The tropics receive more solar energy, which results in higher productivity. This greater productivity may, in turn, contribute indirectly to higher diversity.
4. What is the significance of the slope of regression in a species – area relationship?
ANSWEROn a logarithmic scale the species–area relationship is the straight line log S = log C + Z log A, in which Z is the slope of the line (the regression coefficient). It measures how rapidly species richness (S) increases with area (A).For relatively small areas, the value of Z lies in a narrow range of 0.1 to 0.2, and this is remarkably constant regardless of the taxonomic group or region (plants in Britain, birds in California, molluscs in New York).However, when very large areas such as entire continents are analysed, the slope becomes much steeper, with Z ranging from 0.6 to 1.2 (e.g. 1.15 for frugivorous birds and mammals in tropical forests). A steeper slope therefore indicates that across very large areas, species richness rises much more sharply with increasing area.
5. What are the major causes of species losses in a geographical region?
ANSWERThe accelerated species losses are largely due to human activities, summarised as ‘The Evil Quartet’:(i) Habitat loss and fragmentation – the most important cause; tropical rainforests have shrunk from over 14% to about 6% of land surface, and fragmentation badly affects large-territory and migratory animals.(ii) Over-exploitation – when ‘need’ turns to ‘greed’, e.g. extinction of Steller’s sea cow and the passenger pigeon, and over-harvesting of marine fish.(iii) Alien species invasions – introduced species turning invasive, e.g. the Nile perch wiping out >200 cichlid species in Lake Victoria, and weeds like Parthenium, Lantana and water hyacinth.(iv) Co-extinctions – when one species becomes extinct, its obligately associated species also vanish, e.g. parasites of an extinct host fish, or a partner in a plant–pollinator mutualism.
6. How is biodiversity important for ecosystem functioning?
ANSWERA community with high biodiversity tends to be more stable — it shows little variation in productivity from year to year, and is both resistant and resilient to natural or man-made disturbances and to invasion by alien species.David Tilman’s long-term outdoor-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.This is explained by Paul Ehrlich’s ‘rivet popper hypothesis’: in an aeroplane (the ecosystem) all parts are held by thousands of rivets (species). Losing a few rivets may not affect flight safety at first, but as more are removed the plane becomes dangerously weak — and the loss of rivets on the wings (key species driving major functions) is far more serious than losing rivets on the seats. Thus rich biodiversity is essential for ecosystem health and human survival.
7. What are sacred groves? What is their role in conservation?
ANSWERSacred groves are tracts of forest set aside on religious and cultural grounds, in which all the trees and wildlife are venerated and given total protection by local communities.In India they are found in the Khasi and Jaintia Hills of Meghalaya, the Aravalli Hills of Rajasthan, the Western Ghat regions of Karnataka and Maharashtra, and the Sarguja, Chanda and Bastar areas of Madhya Pradesh.Role in conservation: being completely protected, sacred groves act as refuges for many rare, endemic and threatened species. In Meghalaya, the sacred groves are the last refuges for a large number of rare and threatened plants. They are thus an excellent traditional example of in situ conservation.
8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
ANSWERFlood control: Vegetation (forests and other plants) intercepts rainfall and slows its flow over the ground. Roots increase the porosity of the soil so that water percolates down and is stored as groundwater rather than running off rapidly. This reduces surface run-off and the volume of water reaching rivers at once, thereby preventing floods.Soil erosion control: Plant roots bind soil particles together and hold the soil firmly in place, while the canopy and leaf litter cushion the impact of rain and reduce the speed of wind and flowing water over the surface. This prevents the top fertile soil from being washed or blown away.Therefore the biotic (living) components — chiefly vegetation along with the soil organisms that maintain soil structure — together regulate the water cycle and stabilise the soil, providing these free ecosystem services.
9. The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations to how animals achieved greater diversification?
ANSWERAnimals show far greater diversification than plants because of several adaptive advantages:(i) Mobility and locomotion: Most animals can move, allowing them to escape predators, search out food and mates, and colonise new and varied habitats — opportunities for the evolution of new species. Plants, being largely fixed, lack this advantage.(ii) A nervous system and sense organs: Animals possess a well-developed nervous system, sense organs and the ability to respond quickly to environmental changes, helping them adapt to and survive in diverse, changing conditions.(iii) Varied feeding habits and reproduction: Animals occupy many different feeding niches (herbivores, carnivores, omnivores, parasites), and many show internal fertilisation, parental care and shorter generation times, which together promote rapid speciation and reduce competition by partitioning resources.
10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
ANSWERYes. We may deliberately wish to eliminate disease-causing pathogens and parasites that are harmful to humans, livestock and crops.Examples include the smallpox virus (already eradicated in the wild through vaccination) and the polio virus, and disease-spreading or crop-destroying organisms such as the malaria-causing Plasmodium, plague bacteria and certain pests.Justification: Such species cause large-scale suffering, death and economic loss, and serve no beneficial ecological role for human welfare. Removing them saves millions of human and animal lives and protects food security. This is ethically defensible because the benefit to human and ecosystem health is enormous — though it should be done with great care so that no useful or harmless species is harmed in the process.
Extra Practice Questions
Short Answer Type Questions
Q1. Who popularised the term ‘biodiversity’, and what does it describe?
ANSWERThe term was popularised by the sociobiologist Edward Wilson. It describes the combined diversity at all levels of biological organisation, from macromolecules within cells to biomes.
Q2. What is meant by endemism, and why are biodiversity hotspots important?
ANSWEREndemism means species being confined to a particular region and found nowhere else. Biodiversity hotspots are regions of very high species richness and high endemism; though all 34 hotspots together cover less than 2% of Earth’s land, strict protection of them could reduce ongoing mass extinctions by almost 30%.
Q3. How does the ‘Sixth Extinction’ differ from the previous five mass extinctions?
ANSWERThe difference lies in the rate. The current extinction rate is estimated to be 100 to 1,000 times faster than in pre-human times, and it is driven largely by human activities, whereas the earlier five episodes occurred before humans appeared and at much slower natural rates.
Q4. State the narrowly utilitarian argument for conserving biodiversity.
ANSWERIt says humans derive direct economic benefits from nature — food, firewood, fibre, construction material, industrial products (tannins, dyes, resins, perfumes) and medicines. More than 25% of drugs sold worldwide are plant-derived, and bioprospecting promises further benefits to biodiversity-rich nations.
Q5. List two modern techniques used in ex situ conservation.
ANSWERTwo techniques are cryopreservation of gametes of threatened species in viable, fertile condition, and in vitro fertilisation; others include tissue-culture propagation of plants and storing seeds of different genetic strains in seed banks.
Long Answer Type Questions
Q1. Distinguish between in situ and ex situ conservation, giving Indian examples of each.
ANSWERIn situ (on-site) conservation protects species within their natural habitat, conserving the whole ecosystem — “we save the entire forest to save the tiger.” Its tools include biodiversity hotspots (three of the world’s 34 cover India: Western Ghats–Sri Lanka, Indo-Burma and Himalaya) and India’s legally protected areas: 14 biosphere reserves, 90 national parks, 448 wildlife sanctuaries and many sacred groves (e.g. in Meghalaya). Ex situ (off-site) conservation takes threatened plants and animals out of their habitat and gives them special care in zoological parks, botanical gardens and wildlife safari parks; modern methods include cryopreservation of gametes, in vitro fertilisation, tissue-culture propagation and seed banks. In situ conserves entire communities and natural processes, whereas ex situ targets individual endangered species, including those already extinct in the wild.
Q2. Describe the species–area relationship and explain the significance of its slope (Z).
ANSWERAlexander von Humboldt observed that within a region species richness increases with area, but only up to a limit. For many taxa (angiosperms, birds, bats, freshwater fishes) the relation between species richness (S) and area (A) is a rectangular hyperbola. On a logarithmic scale it becomes the straight line log S = log C + Z log A, where C is the Y-intercept and Z is the slope (regression coefficient). For small to moderate areas Z is remarkably constant at 0.1–0.2, irrespective of taxon or region. However, across very large areas such as whole continents the slope is much steeper, with Z = 0.6–1.2 (e.g. 1.15 for frugivorous birds and mammals in tropical forests). The steeper slope shows that over continental scales, species richness rises far more sharply with area — reflecting the very large numbers of additional species (including endemics) found over vast regions.
Q3. Discuss the three categories of reasons for conserving biodiversity.
ANSWER(i) Narrowly utilitarian: the direct economic products humans get from nature — food, firewood, fibre, construction material, industrial products and medicines. Over 25% of marketed drugs are plant-derived, and 25,000 plant species feature in traditional medicine; bioprospecting promises further benefits. (ii) Broadly utilitarian: the ecosystem services biodiversity provides — the Amazon produces about 20% of atmospheric oxygen by photosynthesis, pollinators (bees, birds, bats) give us fruits and seeds, and there are intangible aesthetic benefits such as walking through woods or listening to birdsong. (iii) Ethical: every species has intrinsic value, regardless of economic worth; we have a moral duty to care for the millions of species we share the planet with and to pass on our biological legacy in good order to future generations.
MCQs
1. The term ‘biodiversity’ was popularised by:
(a) Robert May (b) Edward Wilson (c) Alexander von Humboldt (d) Paul Ehrlich
2. According to Robert May’s conservative estimate, the global species diversity is about:
(a) 1.5 million (b) 20 million (c) 7 million (d) 50 million
3. Among recorded species, the most species-rich animal group is:
(a) fishes (b) mammals (c) birds (d) insects
4. In the species–area relationship on a log scale, the slope Z for small areas usually ranges between:
(a) 0.1 to 0.2 (b) 0.6 to 1.2 (c) 1.0 to 2.0 (d) 2.0 to 3.0
5. The most important cause of biodiversity loss in ‘The Evil Quartet’ is:
(a) over-exploitation (b) alien species invasion (c) habitat loss and fragmentation (d) co-extinction
6. The extinction of cichlid fish in Lake Victoria was caused by the introduction of:
(a) African catfish (b) Nile perch (c) water hyacinth (d) Lantana
7. The ‘rivet popper hypothesis’ was proposed by:
(a) David Tilman (b) Edward Wilson (c) Paul Ehrlich (d) Robert May
8. How many biodiversity hotspots are currently recognised in the world?
(a) 25 (b) 9 (c) 34 (d) 12
9. Which of the following is an ex situ conservation method?
(a) Biosphere reserve (b) National park (c) Sacred grove (d) Cryopreservation of gametes
10. The Convention on Biological Diversity (‘The Earth Summit’) was held in 1992 at:
(a) Johannesburg (b) Rio de Janeiro (c) Stockholm (d) Nagoya
For each question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.
A-R 1. Assertion: Species diversity is generally highest in the tropics.
Reason: Tropical regions have had a long, relatively undisturbed evolutionary time and a constant, productive environment that promotes speciation.
A-R 2. Assertion: India is regarded as one of the mega-diversity countries of the world.
Reason: Although India has only about 2.4% of the world’s land area, its share of global species diversity is about 8.1%.
A-R 3. Assertion: Sacred groves help in conservation of biodiversity.
Reason: Sacred groves are zoological parks where threatened animals are bred in captivity.
A-R 4. Assertion: A community with more species tends to be more stable.
Reason: Tilman’s experiments showed that plots with more species had less year-to-year variation in biomass and higher productivity.
A-R 5. Assertion: When a host fish species becomes extinct, its unique assemblage of parasites also becomes extinct.
Reason: This is an example of over-exploitation of natural resources.
Answer key: 1-(A), 2-(A), 3-(C), 4-(A), 5-(C).
Common Mistakes & Exam Tips
Common mistakes to avoid
Confusing the three levels of biodiversity — remember genetic (within a species), species (between species), ecological (between ecosystems).
Mixing up the two ranges of Z: 0.1–0.2 for small areas, 0.6–1.2 across continents.
Listing only some of the Evil Quartet — all four (habitat loss, over-exploitation, alien invasions, co-extinctions) must be named.
Calling national parks and sanctuaries ex situ — they are in situ; only zoos, gardens, cryopreservation and seed banks are ex situ.
Misquoting India’s figures — 14 biosphere reserves, 90 national parks, 448 wildlife sanctuaries; 2.4% land but 8.1% of global species.
How to score full marks in this chapter
Learn the key named examples and numbers exactly — Edward Wilson, Robert May’s 7 million, the equation log S = log C + Z log A, the Nile perch / cichlid case, Ehrlich’s rivet popper hypothesis, Tilman’s experiments, 34 hotspots (3 in India), and the Rio 1992 / Johannesburg 2002 summits. For 3–5 mark questions, structure answers with clear sub-headings (the three reasons for conservation, the four causes of loss) and give one concrete example for each point.
Frequently Asked Questions
What is Class 12 Biology Chapter 13 Biodiversity and Conservation about?
It studies the variety of life at genetic, species and ecological levels, how many species exist, global patterns of biodiversity (latitudinal gradient and species–area relationship), the causes of biodiversity loss (the Evil Quartet), the reasons for conservation, and in situ and ex situ conservation methods.
What are the three levels of biodiversity?
Genetic diversity (variation within a species), species diversity (variety of species), and ecological or ecosystem diversity (variety of habitats and ecosystems in a region).
What is the difference between in situ and ex situ conservation?
In situ conservation protects species in their natural habitat (hotspots, biosphere reserves, national parks, sanctuaries, sacred groves), while ex situ conservation protects them outside their habitat (zoos, botanical gardens, cryopreservation, seed banks).
Are these Class 12 Biology Chapter 13 solutions free?
Yes. All solutions are free and follow the official NCERT Biology textbook for session 2026–27.
