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CBSE · NCERT
BIOLOGY – CHAPTER 13 : BIODIVERSITY AND CONSERVATION
Chapter-wise Practice Question Paper (Board + Competitive / NEET Level)
General Instructions
- All questions are compulsory. This paper is based on NCERT Class XII Biology, Chapter 13, and includes NEET-style MCQs and Assertion–Reason questions.
- Q.1 to Q.5 are Section A (40 marks): Q.1 has 20 MCQs; Q.2, Q.3, Q.4 and Q.5 have 5 questions each; every question carries 1 mark.
- Q.6 to Q.13 carry 2 marks each; Q.14 to Q.20 carry 3 marks each; Q.21 and Q.22 are case-based questions of 4 marks each; Q.23 to Q.25 carry 5 marks each.
- Internal choice (OR) is given in Q.14 to Q.20 and Q.23 to Q.25. Attempt only one of the alternatives.
- Draw neat, labelled diagrams wherever required. Solutions to all questions are given after the paper.
SECTION – A (Objective Questions · 40 Marks)
Q.1 Choose the correct option.20 × 1 = 20
(i) The term ‘biodiversity’ was popularised by the sociobiologist –
(a) Robert May(b) Edward Wilson(c) Paul Ehrlich(d) Alexander von Humboldt
(ii) The variation in the potency and concentration of reserpine in Rauwolfia vomitoria growing in different Himalayan ranges is an example of –
(a) Species diversity(b) Ecological diversity(c) Alpha diversity(d) Genetic diversity
(iii) The region with the greatest biodiversity on Earth is –
(a) The Amazonian rainforest(b) The Western Ghats(c) The Sundarbans(d) The Great Barrier Reef
(iv) The number of species recorded and described so far is slightly more than –
(a) 0.5 million(b) 1 million(c) 1.5 million(d) 7 million
(v) In the species–area relationship, the value of the slope (Z) of the regression line for smaller areas is generally –
(a) 0.6 to 1.2(b) 0.1 to 0.2(c) 2 to 3(d) Zero
(vi) The relationship between species richness and the explored area was described by –
(a) Alexander von Humboldt(b) Gause(c) Darwin(d) David Tilman
(vii) Which of the following is NOT one of the causes of biodiversity loss (the ‘Evil Quartet’)?
(a) Habitat loss and fragmentation(b) Over-exploitation(c) Alien species invasions(d) Afforestation using native species
(viii) The introduction of the Nile perch into Lake Victoria (East Africa) led to the extinction of –
(a) Tilapia(b) Carp(c) More than 200 species of cichlid fish(d) Catla
(ix) The dodo, a bird, became extinct from –
(a) Madagascar(b) Mauritius(c) Australia(d) Russia
(x) Steller's sea cow, an extinct marine mammal, belonged to –
(a) Russia(b) Australia(c) Mauritius(d) Africa
(xi) If a host fish species becomes extinct, its unique parasites also become extinct. This is called –
(a) Habitat fragmentation(b) Over-exploitation(c) Co-extinction(d) Alien invasion
(xii) Biodiversity hotspots are regions with –
(a) Low species richness and low endemism(b) High species richness and low endemism(c) Low rainfall and sparse vegetation(d) Very high species richness and a high degree of endemism
(xiii) Which of the following is NOT a biodiversity hotspot covering India?
(a) Thar Desert(b) Western Ghats and Sri Lanka(c) Indo-Burma(d) Himalaya
(xiv) The sacred groves of Meghalaya are located in –
(a) Aravalli hills(b) Khasi and Jaintia hills(c) Western Ghats(d) Sarguja
(xv) Which of the following is an ex situ conservation method?
(a) National park(b) Sacred grove(c) Botanical garden(d) Wildlife sanctuary
(xvi) The Earth Summit of 1992 on biodiversity was held at –
(a) Stockholm(b) Kyoto(c) Johannesburg(d) Rio de Janeiro
(xvii) The ‘rivet popper hypothesis’ was proposed by –
(a) Paul Ehrlich(b) David Tilman(c) Robert May(d) Edward Wilson
(xviii) David Tilman's long-term ecosystem experiments found that plots with more species showed –
(a) More year-to-year variation in total biomass(b) Less year-to-year variation in total biomass and higher productivity(c) No change in biomass(d) Lower productivity
(xix) Current species extinction rates are estimated to be about ______ times faster than in the pre-human times.
(a) 10–20(b) 1–2(c) 100 to 1,000(d) 5,000
(xx) Which of the following is an alien invasive species that threatens native species in India?
(a) Neem(b) Mango(c) Peepal(d) Lantana camara
Q.2 Fill in the blanks.5 × 1 = 5
(i) The diversity of alleles/genes within a species is called ______ diversity.
(ii) The value of the slope (Z) of the species–area relationship for small areas is ______.
(iii) Nile perch was introduced into Lake ______.
(iv) Regions with high species richness, high endemism and high habitat loss are called ______.
(v) Conservation of species in their natural habitat is ______ conservation.
Q.3 Write True or False.5 × 1 = 5
(i) Species diversity generally decreases from the equator towards the poles.
(ii) Species richness keeps increasing indefinitely with the explored area.
(iii) The dodo became extinct from Mauritius.
(iv) Botanical gardens are an example of in situ conservation.
(v) Sacred groves protect biodiversity in India through religious beliefs.
Q.4 Match Column ‘A’ with Column ‘B’.5 × 1 = 5
| Column ‘A’ | Column ‘B’ |
|---|---|
| (i) Dodo | (a) Russia |
| (ii) Quagga | (b) Mauritius |
| (iii) Thylacine | (c) Lake Victoria |
| (iv) Steller's sea cow | (d) Australia |
| (v) Nile perch | (e) Africa |
Q.5 Assertion (A) – Reason (R) type questions. Choose: (a) Both A and R true, R explains A; (b) Both true, R does not explain A; (c) A true, R false; (d) A false, R true.5 × 1 = 5
(i) Assertion (A): Tropical regions harbour more species than temperate regions.
Reason (R): Tropical environments are less seasonal, more constant and predictable, have received more solar energy and had a long evolutionary time undisturbed by glaciation.
Reason (R): Tropical environments are less seasonal, more constant and predictable, have received more solar energy and had a long evolutionary time undisturbed by glaciation.
(ii) Assertion (A): Habitat loss and fragmentation is the most important cause of biodiversity loss.
Reason (R): Tropical rainforests that once covered 14 per cent of the land surface now cover no more than 6 per cent.
Reason (R): Tropical rainforests that once covered 14 per cent of the land surface now cover no more than 6 per cent.
(iii) Assertion (A): On a logarithmic scale the species–area relationship is a straight line.
Reason (R): The slope (Z) is always between 0.6 and 1.2 irrespective of the area.
Reason (R): The slope (Z) is always between 0.6 and 1.2 irrespective of the area.
(iv) Assertion (A): Biodiversity hotspots are found only in India.
Reason (R): There are 34 biodiversity hotspots in the world.
Reason (R): There are 34 biodiversity hotspots in the world.
(v) Assertion (A): Ex situ conservation is needed for the threatened species of animals and plants.
Reason (R): Their natural habitats have become so degraded that they cannot survive there.
Reason (R): Their natural habitats have become so degraded that they cannot survive there.
SECTION – B (Very Short Answer · 2 Marks each)
6. Define biodiversity. Name its three levels.(2)
7. What is the species–area relationship? Write its equation.(2)
8. What is the ‘Evil Quartet’? Name its four components.(2)
9. What is co-extinction? Give an example.(2)
10. What are biodiversity hotspots? Name the three hotspots that cover India.(2)
11. What are sacred groves? State their importance.(2)
12. Give two examples of alien species invasions and their effects.(2)
13. Differentiate between in situ and ex situ conservation.(2)
SECTION – C (Short Answer · 3 Marks each)
14. Explain the latitudinal gradient of species diversity with examples.(3)
OR
Explain the species–area relationship with the equation and the value of Z.
15. Give reasons why the tropics have greater species diversity.(3)
OR
Explain the importance of species diversity to the ecosystem (Tilman and the rivet popper hypothesis).
16. Describe habitat loss and fragmentation and over-exploitation as the causes of biodiversity loss.(3)
OR
Describe alien species invasions and co-extinctions as causes of biodiversity loss.
17. Explain in situ conservation. What are biodiversity hotspots and sacred groves?(3)
OR
Explain ex situ conservation with examples.
18. Why should we conserve biodiversity? Explain the three categories of reasons.(3)
OR
Describe the extinction of species: examples and the present rate of extinction.
19. What are biodiversity hotspots? Write the criteria and the three hotspots in India.(3)
OR
Explain the role of international conventions in conserving biodiversity (Earth Summit, Johannesburg Summit).
20. Describe the three levels of biodiversity with examples.(3)
OR
Describe the global and Indian diversity of species.
SECTION – D (Case-Based Questions · 4 Marks each)
21. Read the passage and answer the questions that follow.(4)
In the 1950s, the Nile perch, a large predatory fish, was introduced into Lake Victoria in East Africa. Soon it led to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake. In India, the African catfish Clarias gariepinus introduced for aquaculture is threatening the indigenous catfishes.
(i) Name the type of threat to biodiversity illustrated here.(1)
(ii) What are alien (exotic) species?(1)
(iii) Give two other examples of invasive alien species in India and state one measure to control such invasions.(2)
22. Read the passage and answer the questions that follow.(4)
A researcher plotted species richness against the area of study for the vascular plants of a region on a log–log scale, and obtained a straight line with a slope of 0.15.
(i) Write the equation of this species–area relationship.(1)
(ii) Is the slope of 0.15 consistent with the typical range for small areas? State the range.(1)
(iii) What would be the expected slope if the whole continents are analysed, and what does it indicate?(2)
SECTION – E (Long Answer · 5 Marks each)
23. Describe the patterns of biodiversity: the latitudinal gradient and the species–area relationship. Why is species diversity important to the ecosystem?(5)
OR
Explain the causes of biodiversity loss (the ‘Evil Quartet’) with suitable examples.
24. Why should biodiversity be conserved? Describe the narrowly utilitarian, broadly utilitarian and ethical arguments, and state the approaches to conservation.(5)
OR
Describe in situ and ex situ conservation of biodiversity in detail.
25. Describe the three levels of biodiversity and the global and Indian diversity of species.(5)
OR
Describe the loss of biodiversity: its consequences, the rate of extinction and the international efforts for conservation.
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CBSE · NCERT
BIOLOGY – CHAPTER 13 : COMPLETE SOLUTIONS
Biodiversity and Conservation · Answer Key with Step-by-Step Explanations
Q.1 Quick Answer Key (MCQ)20 × 1 = 20
| i | (b) | ii | (d) | iii | (a) | iv | (c) | v | (b) |
| vi | (a) | vii | (d) | viii | (c) | ix | (b) | x | (a) |
| xi | (c) | xii | (d) | xiii | (a) | xiv | (b) | xv | (c) |
| xvi | (d) | xvii | (a) | xviii | (b) | xix | (c) | xx | (d) |
Q.1 Solutions with Explanation
(i) Ans. (b) Edward Wilson
Edward Wilson popularised the term; it includes the diversity at all levels of the biological hierarchy – genes, species and ecosystems.
(ii) Ans. (d) Genetic diversity
Variation within a species (here the medicinal plant) is genetic diversity; India has over 50,000 genetically different strains of rice and 1,000 varieties of mango.
(iii) Ans. (a) The Amazonian rainforest
The Amazonian rainforest in South America has the greatest biodiversity: more than 40,000 species of plants, 3,000 of fishes, 1,300 of birds, 427 of mammals and 427 of amphibians.
(iv) Ans. (c) 1.5 million
Slightly more than 1.5 million species have been described; Robert May's global estimate is about 7 million.
(v) Ans. (b) 0.1 to 0.2
Z lies in the range 0.1–0.2 regardless of the taxonomic group or the region; for very large areas (whole continents) it is 0.6–1.2.
(vi) Ans. (a) Alexander von Humboldt
Alexander von Humboldt observed that within a region species richness increases with increasing explored area, but only up to a limit.
(vii) Ans. (d) Afforestation using native species
The Evil Quartet is: habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinctions.
(viii) Ans. (c) More than 200 species of cichlid fish
It caused the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake.
(ix) Ans. (b) Mauritius
The dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia) and three subspecies of tiger (Bali, Javan, Caspian) are the examples of recent extinctions.
(x) Ans. (a) Russia
Steller's sea cow was a marine mammal of Russia (Bering Sea region), hunted to extinction.
(xi) Ans. (c) Co-extinction
Co-extinction – when a species becomes extinct, the plants and animals associated with it in an obligatory way also become extinct (e.g. a coevolved plant–pollinator mutualism).
(xii) Ans. (d) Very high species richness and a high degree of endemism
Initially 25 hotspots were identified, now 34; they are also regions of accelerated habitat loss.
(xiii) Ans. (a) Thar Desert
The three hotspots covering India are the Western Ghats and Sri Lanka, Indo-Burma and the Himalaya.
(xiv) Ans. (b) Khasi and Jaintia hills
Sacred groves are tracts of forest set aside, with all the trees and wildlife within them protected; 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.
(xv) Ans. (c) Botanical garden
Ex situ – outside the natural habitat: zoological parks, botanical gardens, wildlife safari parks, cryopreservation, seed banks, in vitro fertilisation and tissue culture.
(xvi) Ans. (d) Rio de Janeiro
The Convention on Biological Diversity was held at Rio de Janeiro in 1992; the World Summit on Sustainable Development (2002) was held at Johannesburg, South Africa.
(xvii) Ans. (a) Paul Ehrlich
Ehrlich compared the ecosystem to an airplane where each species is a rivet; losing a few rivets may not matter at first, but losing key rivets leads to a crash.
(xviii) Ans. (b) Less year-to-year variation in total biomass and higher productivity
Increased diversity contributed to higher productivity and greater stability of the community.
(xix) Ans. (c) 100 to 1,000
Humans are mainly responsible for this rapid loss, the so-called sixth extinction.
(xx) Ans. (d) Lantana camara
Alien species such as carrot grass (Parthenium), Lantana and water hyacinth (Eichhornia) have caused environmental damage and the decline of indigenous species.
Q.2 Fill in the blanks5 × 1 = 5
(i) Genetic
(ii) 0.1 to 0.2
(iii) Victoria
(iv) Biodiversity hotspots
(v) In situ
Q.3 True / False5 × 1 = 5
(i) True.
Tropical areas harbour more species than temperate or polar areas.
(ii) False.
It increases with area but only up to a limit; the curve becomes a plateau.
(iii) True.
It is one of the recent extinctions.
(iv) False.
They are an ex situ conservation method.
(v) True.
All the trees and wildlife within them are traditionally protected.
Q.4 Matching5 × 1 = 5
(i) – (b) · (ii) – (e) · (iii) – (d) · (iv) – (a) · (v) – (c)
Dodo – Mauritius; quagga – Africa; thylacine – Australia; Steller’s sea cow – Russia; Nile perch – introduced in Lake Victoria.
Q.5 Assertion – Reason5 × 1 = 5
(i) Ans. (a)
Both true; these factors promote niche specialisation and hence greater species diversity.
(ii) Ans. (b)
Both true; R is an example (a fact) that supports the cause, but it does not by itself explain A.
(iii) Ans. (c)
A is true. R is false: Z is 0.1–0.2 for smaller areas; 0.6–1.2 only for very large areas such as whole continents.
(iv) Ans. (d)
A is false (there are hotspots in many countries; three cover India). R is true.
(v) Ans. (a)
Both true; such species are taken out and placed in special settings (zoological parks, botanical gardens, gene banks) where they can be protected.
SECTION – B (2 Marks each)
6. Ans.
Biodiversity is the sum total of the diversity of all living organisms on Earth, at all levels of the biological hierarchy from genes to ecosystems. [1] Levels: genetic diversity, species diversity and ecological diversity. [1]
7. Ans.
Within a region, species richness increases with increasing explored area, but only up to a limit (Alexander von Humboldt). [1] The relationship on a logarithmic scale is a straight line: log S = log C + Z log A, where S = species richness, A = area, Z = slope of the line (regression coefficient) and C = Y-intercept. [1]
8. Ans.
‘The Evil Quartet’ is the term used by Jared Diamond for the four major causes of biodiversity losses. [1] They are: (i) habitat loss and fragmentation; (ii) over-exploitation; (iii) alien species invasions; (iv) co-extinctions. [1]
9. Ans.
When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. [1] Example: when a host fish species becomes extinct, the parasites exclusive to it also become extinct; the coevolved plant–pollinator mutualism. [1]
10. Ans.
Biodiversity hotspots are regions with very high levels of species richness and a high degree of endemism (also regions of accelerated habitat loss). [1] The three hotspots covering India are: Western Ghats and Sri Lanka, Indo-Burma and the Himalaya. [1]
11. Ans.
Sacred groves are tracts of forest set aside in many cultures, where all the trees and wildlife within are venerated and given total protection. [1] They are found in the Khasi and Jaintia Hills (Meghalaya), the Aravalli Hills (Rajasthan), the Western Ghats and other areas, and conserve rare, threatened species and often endemic plants. [1]
12. Ans.
Nile perch introduced into Lake Victoria caused the extinction of more than 200 species of cichlid fish. [1] Water hyacinth (Eichhornia), Lantana and carrot grass (Parthenium) are invasive weeds that harm native species; the African catfish Clarias gariepinus threatens the indigenous catfishes of Indian rivers. (Any two) [1]
13. Ans.
In situ conservation: protection of the species in its natural habitat (biosphere reserves, national parks, sanctuaries, sacred groves). [1] Ex situ conservation: threatened species are taken out of their habitat and placed in special settings, e.g. zoological parks, botanical gardens, gene banks/seed banks. [1]
SECTION – C (3 Marks each)
14. Ans.
Species diversity decreases from the equator towards the poles; with very few exceptions, tropics harbour more species than temperate or polar areas. [1] Examples: Colombia (near the equator) has nearly 1,400 species of birds, New York (41° N) has 105, Greenland (71° N) has 56 and India (23°N) has 1,200. [1] The tropical Amazonian rainforest has the greatest biodiversity (over 40,000 plant species, 3,000 fish species, 1,300 birds, 427 mammals and 427 amphibians). [1]
OR
Alexander von Humboldt observed that within a region species richness increases with increasing explored area but only up to a limit. [1] On a log scale it is a straight line: log S = log C + Z log A (S – species richness, A – area, Z – slope, C – Y-intercept). [1] The value of Z is 0.1–0.2 regardless of the taxonomic group or region, but for very large areas, e.g. analysis of species–area relationships among very large areas like the entire continents, the slope is much steeper (Z = 0.6–1.2). [1]
15. Ans.
(i) Temperate regions were subjected to frequent glaciations in the past, whereas tropical latitudes have remained relatively undisturbed for millions of years, so a long evolutionary time was available for species diversification. [1] (ii) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable; this promotes niche specialisation and greater species diversity. [1] (iii) There is more solar energy available in the tropics, which contributes to higher productivity, and indirectly greater diversity. [1]
OR
Tilman's experiments: plots with more species showed less year-to-year variation in total biomass and, in general, higher productivity; thus diversity brings stability. [1½] Rivet popper hypothesis (Paul Ehrlich): in an airplane (ecosystem) all parts are joined together by rivets (species); loss of a rivet may not affect the flight initially, but removal of the key rivets (key species) causes a crash; a species may play a key role in the functioning of the ecosystem. [1½]
16. Ans.
Habitat loss and fragmentation is the most important cause of the extinction of animals and plants: the tropical rainforests that once covered more than 14 per cent of the land surface now cover no more than 6 per cent; the Amazon rainforest is being cut for cultivating soya beans or for conversion into grasslands for beef cattle. [1½] Pollution adds to the degradation of habitats; when large habitats are broken into small fragments, the animals requiring large territories (migratory birds, mammals) and those with a particular need are badly affected. [½] Over-exploitation: humans have always depended on nature for food and shelter, but when the ‘need’ turns to ‘greed’, it leads to over-exploitation of natural resources; the passenger pigeon was hunted to extinction, and many marine fish stocks are declining. [1]
OR
Alien species invasions: when alien species are introduced unintentionally or deliberately, some of them turn invasive and cause the decline or extinction of indigenous species. [1] Examples: the Nile perch in Lake Victoria; invasive weeds like carrot grass (Parthenium), Lantana and water hyacinth; the illegal introduction of the African catfish Clarias gariepinus for aquaculture is posing a threat to the indigenous catfishes in Indian rivers. [1] Co-extinctions: when a species becomes extinct, the plants and animals associated with it in an obligatory way also become extinct; e.g. the extinction of a host fish species leads to the extinction of its parasites. [1]
17. Ans.
In situ conservation – the conservation of species in its natural habitat; the biodiversity-rich areas are protected as biosphere reserves, national parks and sanctuaries. [1] Biodiversity hotspots – regions with very high species richness and endemism; 34 in the world, three of which (Western Ghats and Sri Lanka, Indo-Burma, Himalaya) cover India. [1] Sacred groves – forest tracts protected by religious and cultural traditions, in Meghalaya, Rajasthan, Karnataka, Maharashtra, etc. [1]
OR
Ex situ conservation – the threatened animals and plants are taken out of their natural habitat and placed in special settings where they can be protected and given special care. [1] Examples: zoological parks, botanical gardens and wildlife safari parks. [1] Gametes of threatened species can be preserved in viable and fertile condition for long periods by cryopreservation; eggs can be fertilised in vitro, and plants can be propagated through tissue culture; seeds of different genetic strains of commercially important plants can be kept in seed banks. [1]
18. Ans.
Narrowly utilitarian: humans derive countless direct economic benefits from nature – food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes) and products of medicinal importance (more than 25 per cent of the drugs in the market are derived from plants; bioprospecting). [1] Broadly utilitarian: biodiversity plays a major role in many ecosystem services – the Amazon forest produces, through photosynthesis, 20 per cent of the total oxygen in the Earth's atmosphere; pollination, aesthetic pleasures. [1] Ethical: every species has an intrinsic value, even if it is not of current economic value to us; we have a moral duty to care for their well-being and pass on our biological legacy to future generations. [1]
OR
Over the 3.8 billion years of life on Earth, there have been five episodes of mass extinction; the current extinction (sixth) rate is 100 to 1,000 times faster than in the pre-human times, mainly due to human activities. [1] According to the IUCN Red List (2004), 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) became extinct in the last 500 years. [1] Examples: the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia), and three subspecies of tiger (Bali, Javan, Caspian). [1]
19. Ans.
Biodiversity hotspots are regions with very high levels of species richness and a high degree of endemism (species that are not found anywhere else); they are also regions of accelerated habitat loss. [1½] Originally 25 hotspots were identified for the priority of conservation; now 34 are recognised, together covering less than 2 per cent of the Earth's land area, but their conservation reduces the mass extinction. [1] The three covering India: Western Ghats and Sri Lanka, Indo-Burma and the Himalaya. [½]
OR
In 1992, at the Earth Summit in Rio de Janeiro, the Convention on Biological Diversity was held, in which all nations were called upon to take appropriate measures for conservation of biodiversity and sustainable utilisation of its benefits. [1½] In 2002, at the World Summit on Sustainable Development in Johannesburg (South Africa), 190 countries pledged their commitment to achieve by 2010 a significant reduction in the current rate of biodiversity loss at global, regional and local levels. [1½]
20. Ans.
Genetic diversity: variation in the genes within a species, e.g. the potency and concentration of reserpine in Rauwolfia vomitoria in different Himalayan ranges; India has over 50,000 genetically different strains of rice and 1,000 varieties of mango. [1] Species diversity: the diversity at the species level, e.g. the Western Ghats have a greater amphibian species diversity than the Eastern Ghats. [1] Ecological diversity: at the ecosystem level, e.g. India, with its deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows, has a greater ecosystem diversity than a Scandinavian country like Norway. [1]
OR
According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million. [1] Robert May's global estimate is about 7 million. More than 70 per cent of all species recorded are animals, while plants comprise no more than 22 per cent; among animals, insects are the most species-rich group (about 70 per cent). The number of fungi species in the world is more than the combined total of the species of fishes, amphibians, reptiles and mammals. [1] India has only 2.4 per cent of the world's land area but its share of the global species diversity is an impressive 8.1 per cent – one of the 12 mega diversity countries of the world. [1]
SECTION – D (Case-Based · 4 Marks each)
21. Ans.
(i) Alien species invasion (one of the components of the ‘Evil Quartet’). [1]
(ii) Species that are introduced unintentionally or deliberately into an area where they are not native; some of them become invasive and harm the indigenous species. [1]
(iii) Lantana camara, water hyacinth (Eichhornia) and carrot grass (Parthenium). [1] Measure: strict quarantine/regulation on the introduction of exotic species, and early detection with removal or biological control of invasive species. [1] [2]
22. Ans.
(i) log S = log C + Z log A, where S = species richness, A = area, Z = slope of the line and C = Y-intercept. [1]
(ii) Yes; the range of Z is 0.1–0.2 regardless of the taxonomic group or the region. [1]
(iii) The slope is much steeper, Z = 0.6–1.2. [1] It indicates that, over large areas, species richness increases much faster with increasing area (more habitats, more species) than in smaller areas. [1] [2]
SECTION – E (Long Answer · 5 Marks each)
23. Ans.
Latitudinal gradient: species diversity decreases from the equator to the poles; Colombia 1,400 bird species, New York 105, Greenland 56, India 1,200; Amazon rainforest has the greatest diversity. [1] Causes: tropical regions had a long, undisturbed evolutionary time; a more constant, predictable and less seasonal environment (niche specialisation); more solar energy (higher productivity). [1]
Species–area relationship: Humboldt; richness increases with area up to a limit; log S = log C + Z log A; Z = 0.1–0.2 for small areas and 0.6–1.2 for continents. [1½]
Importance of species diversity: Tilman – more species gives less year-to-year variation in biomass and higher productivity; Ehrlich's rivet popper hypothesis – loss of key species affects ecosystem function. [1½]
Species–area relationship: Humboldt; richness increases with area up to a limit; log S = log C + Z log A; Z = 0.1–0.2 for small areas and 0.6–1.2 for continents. [1½]
Importance of species diversity: Tilman – more species gives less year-to-year variation in biomass and higher productivity; Ehrlich's rivet popper hypothesis – loss of key species affects ecosystem function. [1½]
OR
1. Habitat loss and fragmentation: the most important cause; tropical rainforests reduced from 14% to 6% of the land surface; the Amazon forest is cut for soya beans and cattle; pollution; fragmentation affects animals needing large territories. [1½]
2. Over-exploitation: ‘need’ turns into ‘greed’; the passenger pigeon and Steller's sea cow are extinct; many marine fish stocks are depleted. [1]
3. Alien species invasions: Nile perch (Lake Victoria – over 200 cichlid species lost); Parthenium, Lantana, Eichhornia; African catfish Clarias gariepinus. [1½]
4. Co-extinctions: the extinction of a species causes the extinction of the species associated with it, e.g. host–parasite and plant–pollinator. [1]
2. Over-exploitation: ‘need’ turns into ‘greed’; the passenger pigeon and Steller's sea cow are extinct; many marine fish stocks are depleted. [1]
3. Alien species invasions: Nile perch (Lake Victoria – over 200 cichlid species lost); Parthenium, Lantana, Eichhornia; African catfish Clarias gariepinus. [1½]
4. Co-extinctions: the extinction of a species causes the extinction of the species associated with it, e.g. host–parasite and plant–pollinator. [1]
24. Ans.
Narrowly utilitarian: food, firewood, fibre, construction material, industrial products and medicines (more than 25% of the drugs are plant-derived; bioprospecting). [1½]
Broadly utilitarian: ecosystem services – the Amazon forest provides 20% of the Earth's oxygen; pollination; aesthetic pleasure. [1]
Ethical: every species has an intrinsic value; we have a moral duty to pass on our biological legacy to future generations. [1]
Approaches: in situ (protect in natural habitats) and ex situ (outside the habitat – zoological parks, botanical gardens, gene banks). [1½]
Broadly utilitarian: ecosystem services – the Amazon forest provides 20% of the Earth's oxygen; pollination; aesthetic pleasure. [1]
Ethical: every species has an intrinsic value; we have a moral duty to pass on our biological legacy to future generations. [1]
Approaches: in situ (protect in natural habitats) and ex situ (outside the habitat – zoological parks, botanical gardens, gene banks). [1½]
OR
In situ conservation: conserve the species in its natural habitat. Biodiversity hotspots (34 in the world; Western Ghats and Sri Lanka, Indo-Burma and Himalaya in India) and legally protected areas – biosphere reserves, national parks and sanctuaries; sacred groves (Khasi and Jaintia Hills, Aravalli Hills, Western Ghats, Sarguja, Chanda and Bastar) protected by cultural beliefs. [2½]
Ex situ conservation: threatened species are taken out of the habitat and kept in zoological parks, botanical gardens and wildlife safari parks; gametes are preserved by cryopreservation; in vitro fertilisation, tissue culture propagation; seed banks of different genetic strains of crops. [2½]
Ex situ conservation: threatened species are taken out of the habitat and kept in zoological parks, botanical gardens and wildlife safari parks; gametes are preserved by cryopreservation; in vitro fertilisation, tissue culture propagation; seed banks of different genetic strains of crops. [2½]
25. Ans.
Three levels: genetic diversity (variation within a species – 50,000 strains of rice, 1,000 mango varieties; reserpine in Rauwolfia); species diversity (Western Ghats vs Eastern Ghats amphibians); ecological diversity (India vs Norway). [2]
Global diversity: over 1.5 million species described; Robert May – about 7 million; more than 70% are animals (insects about 70% of the animals) and plants about 22%; fungi species outnumber the total of fishes, amphibians, reptiles and mammals together. [1½]
India: 2.4% of the land area but 8.1% of global species diversity; one of the 12 mega-diversity countries. [1]
Patterns: highest in the tropics (Amazon). [½]
Global diversity: over 1.5 million species described; Robert May – about 7 million; more than 70% are animals (insects about 70% of the animals) and plants about 22%; fungi species outnumber the total of fishes, amphibians, reptiles and mammals together. [1½]
India: 2.4% of the land area but 8.1% of global species diversity; one of the 12 mega-diversity countries. [1]
Patterns: highest in the tropics (Amazon). [½]
OR
Extinction: five mass extinctions in the past; the current (sixth) extinction rate is 100–1,000 times faster than in pre-human times; 784 species became extinct in the last 500 years (338 vertebrates, 359 invertebrates, 87 plants) – dodo, quagga, thylacine, Steller's sea cow, three subspecies of tiger. [1½]
Consequences: decline in plant production, lowered resistance to environmental perturbations such as drought, increased variability in ecosystem processes such as plant productivity, water use, pest and disease cycles. [1½]
International efforts: Earth Summit 1992 (Rio de Janeiro, Convention on Biological Diversity); World Summit on Sustainable Development 2002 (Johannesburg) – 190 countries pledged to reduce biodiversity loss by 2010. [2]
Consequences: decline in plant production, lowered resistance to environmental perturbations such as drought, increased variability in ecosystem processes such as plant productivity, water use, pest and disease cycles. [1½]
International efforts: Earth Summit 1992 (Rio de Janeiro, Convention on Biological Diversity); World Summit on Sustainable Development 2002 (Johannesburg) – 190 countries pledged to reduce biodiversity loss by 2010. [2]
QUICK REVISION · HIGH-YIELD POINTS (NEET / CBSE)
- Biodiversity (Edward Wilson): genetic (reserpine in Rauwolfia; 50,000 rice strains), species (Western vs Eastern Ghats amphibians) and ecological diversity (India vs Norway).
- Global: over 1.5 million species described; Robert May – about 7 million; animals over 70% (insects about 70% of animals), plants about 22%. India – 2.4% land area, 8.1% species; one of 12 mega-diversity countries.
- Latitudinal gradient: diversity falls from equator to poles (Colombia 1,400 birds; New York 105; Greenland 56; India 1,200). Reasons: long evolutionary time, constant environment, more solar energy.
- Species–area relationship (Humboldt): log S = log C + Z log A; Z = 0.1–0.2 (small areas), 0.6–1.2 (continents).
- Importance: Tilman – more species, less variation in biomass, higher productivity; Ehrlich's rivet popper hypothesis.
- Loss: 784 extinctions in 500 years – dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller's sea cow (Russia), 3 tiger subspecies; present rate 100–1,000 times faster (sixth extinction).
- Evil Quartet: habitat loss and fragmentation (rainforest 14% to 6%), over-exploitation, alien species invasions (Nile perch, Parthenium, Lantana, Eichhornia, Clarias gariepinus), co-extinctions.
- Reasons to conserve: narrowly utilitarian (drugs, food), broadly utilitarian (Amazon 20% oxygen, pollination), ethical (intrinsic value).
- In situ: 34 hotspots (India – Western Ghats and Sri Lanka, Indo-Burma, Himalaya), biosphere reserves, national parks, sanctuaries, sacred groves. Ex situ: zoos, botanical gardens, cryopreservation, in vitro fertilisation, tissue culture, seed banks.
- Earth Summit, Rio de Janeiro 1992 (Convention on Biological Diversity); Johannesburg 2002 – 190 countries pledged to reduce biodiversity loss by 2010.
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