Chapter 13: Biodiversity and Conservation Long Questions | biology Class 12 CBSE

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Chapter 13: Biodiversity and Conservation Long Questions | biology Class 12 CBSE | ByteNotes.in

Long Answer

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Question 1

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Analyse the three hypotheses proposed to explain why the tropics show the greatest levels of species richness.

The speciation-time hypothesis states that unlike temperate regions subjected to frequent glaciations, tropical latitudes have remained relatively undisturbed for millions of years, providing a longer evolutionary time for species diversification.
The environmental constancy hypothesis argues that tropical environments are less seasonal, more constant and predictable than temperate ones, promoting niche specialisation and thereby supporting greater species diversity.
The productivity hypothesis proposes that more solar energy is available in the tropics, contributing to higher primary productivity, which in turn indirectly supports greater species diversity at higher trophic levels.
These three hypotheses are not mutually exclusive; all three factors — time, environmental stability and energy — likely work together to produce and maintain the extraordinarily high biodiversity seen in tropical regions.
The Amazonian rainforest exemplifies this richness: it hosts over 40,000 plant species, 3,000 fish species and more than 1,25,000 invertebrate species, illustrating the combined outcome of these evolutionary and ecological processes.

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Question 2

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Compare and contrast in situ and ex situ conservation strategies with suitable examples from India.

In situ conservation protects species within their natural habitats, preserving not just individual species but entire ecosystems and all ecological interactions; India achieves this through 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries.
Biodiversity hotspots — regions of high species richness and endemism — are prioritised for in situ conservation; India's three hotspots are the Western Ghats and Sri Lanka, Indo-Burma and the Himalaya.
Sacred groves represent culturally embedded in situ conservation, found in Meghalaya, Rajasthan, Karnataka, Maharashtra and Madhya Pradesh, often protecting rare and threatened plants as the last refuges.
Ex situ conservation removes threatened organisms from nature for protection in zoological parks, botanical gardens or wildlife safari parks; modern methods include cryopreservation of gametes, in vitro fertilisation, tissue culture of plants and seed banks.
In situ conservation is preferred as it maintains natural processes, but ex situ is indispensable when a species faces imminent wild extinction; ideally, both strategies should complement each other.

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Hard

Question 3

Long Form

Discuss the four causes of biodiversity loss known as the 'Evil Quartet' with examples.

Habitat loss and fragmentation is the most critical cause; tropical rainforests once covered 14 per cent of Earth's land area but now cover only 6 per cent, with the Amazon being cleared for soya and beef cattle, destroying millions of species' homes.
Over-exploitation occurs when human greed replaces need; species such as Steller's sea cow and the passenger pigeon were hunted to extinction, and many marine fish populations are currently over-harvested beyond sustainable limits.
Alien species invasions involve introduced species turning invasive; Nile perch in Lake Victoria eliminated over 200 cichlid fish species, while Parthenium, Lantana, water hyacinth and the African catfish Clarias gariepinus threaten native species in India.
Co-extinctions occur through obligatory interdependencies; when a host fish species becomes extinct, its associated parasites disappear, and in coevolved plant-pollinator mutualisms, extinction of one invariably leads to extinction of the other.
These four causes interact and amplify each other — habitat loss weakens populations making them more vulnerable to exploitation and invasions, while co-extinctions cascade through food webs, multiplying the actual number of species lost.

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Question 4

Long Form

Explain the three arguments for biodiversity conservation and assess their relative importance.

The narrowly utilitarian argument emphasises direct economic benefits: food, firewood, fibre, industrial products (tannins, dyes, resins, perfumes) and medicines — over 25 per cent of global drugs are plant-derived, and 25,000 plant species contribute to traditional medicines worldwide.
The broadly utilitarian argument covers ecosystem services: the Amazon produces 20 per cent of atmospheric oxygen; pollinators enable fruit and seed production; biodiversity supports flood control, pest regulation, climate moderation and aesthetic pleasures whose monetary value is immeasurable.
Bioprospecting extends the utilitarian case further — exploring biodiversity for economically important molecules and genes promises enormous economic returns for biodiverse nations, particularly from tropical rainforests yet to be fully explored.
The ethical argument transcends economics: every species has intrinsic value irrespective of usefulness to humans; we share this planet with millions of organisms and bear a moral duty to care for them and pass our biological legacy to future generations.
While all three arguments are important, the ethical argument may be the most foundational — it provides a reason to conserve even those species with no known economic value, ensuring comprehensive rather than selective conservation.

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Question 5

Long Form

Explain the species-area relationship discovered by Alexander von Humboldt and discuss the significance of different Z values.

Alexander von Humboldt observed during his explorations in South American jungles that species richness increased with increasing explored area, but only up to a limit, forming a rectangular hyperbola relationship.
On a logarithmic scale, the relationship is a straight line described by: log S = log C + Z log A, where S is species richness, A is area, Z is the regression coefficient (slope) and C is the y-intercept.
For smaller, regional areas, Z values lie in the range of 0.1 to 0.2 regardless of taxonomic group or region — whether plants in Britain, birds in California or molluscs in New York — showing remarkable consistency.
For very large areas such as entire continents, Z values range from 0.6 to 1.2; for frugivorous birds and mammals in tropical forests of different continents, the slope is 1.15, indicating species richness increases much more steeply with area at continental scales.
The steeper slope at continental scales implies that large-scale habitat destruction eliminates proportionally far more species than small-scale habitat loss, underlining why preserving large intact habitats is critical for biodiversity conservation.

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Question 6

Long Form

Evaluate the role of biodiversity in ecosystem functioning using David Tilman's findings and Paul Ehrlich's analogy.

David Tilman's long-term outdoor plot experiments demonstrated that plots with more species showed less year-to-year variation in total biomass, indicating greater ecosystem stability with higher species richness.
Tilman also showed that increased species diversity contributed to higher productivity, providing empirical evidence for the positive relationship between biodiversity and ecosystem function.
A stable ecosystem must not show excessive variation in productivity, must be resilient to natural and human disturbances, and must resist invasion by alien species — all attributes promoted by high species richness.
Paul Ehrlich's rivet popper hypothesis uses the analogy of an airplane (ecosystem) held together by rivets (species); passengers removing rivets (humans causing extinctions) progressively weaken the structure, with loss of wing rivets (keystone species) being most catastrophic.
Together, these perspectives show that biodiversity underpins ecosystem health and human survival — rich biodiversity is not just aesthetically pleasing but is functionally imperative for maintaining the services on which all life depends.

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Medium

Question 7

Long Form

Discuss the current state of global and Indian biodiversity loss, including key statistics on threatened species and the rate of extinction.

The IUCN Red List (2004) documents the extinction of 784 species in the last 500 years, including 338 vertebrates, 359 invertebrates and 87 plants; examples include the dodo, quagga, thylacine and Steller's Sea Cow.
Currently, more than 15,500 species worldwide face the threat of extinction; 12 per cent of bird species, 23 per cent of mammal species, 32 per cent of amphibian species and 31 per cent of gymnosperm species are threatened.
Current extinction rates are estimated to be 100 to 1,000 times faster than pre-human (natural) rates, constituting the 'sixth mass extinction' — the first five were caused by natural events over geological time.
India is particularly affected: over 650 species from India are among those currently threatened; the colonisation of tropical Pacific Islands by humans led to the extinction of more than 2,000 native bird species, illustrating human impact.
If present trends continue, ecologists warn that nearly half of all species on Earth could be wiped out within the next 100 years, making urgent conservation action a biological and ethical imperative.

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Hard

Question 8

Long Form

How do ecologists estimate global species richness? Discuss the limitations of current estimates and India's undiscovered species.

Ecologists estimate global species richness by statistically comparing the temperate-tropical species richness of exhaustively studied insect groups and extrapolating this ratio to other animal and plant taxa.
Although IUCN records about 1.5 million described species, estimates of total species vary widely from 20–50 million, with Robert May's conservative estimate placing global diversity at approximately 7 million.
A key limitation is that conventional taxonomic methods cannot identify many microbial species, and many prokaryotes cannot be cultured in laboratory conditions; if molecular or biochemical criteria are used, microbial diversity alone might run into millions.
Only about 22 per cent of the total species are estimated to have been recorded so far, leaving about 78 per cent undiscovered; applying this to India, there are likely over 1,00,000 undiscovered plant species and over 3,00,000 undiscovered animal species.
A further complication is that many undiscovered species face extinction before being catalogued — as the chapter states, 'nature's biological library is burning even before we have catalogued all its books', making rapid biodiversity inventories urgent.

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Question 9

Long Form

Analyse why amphibians appear to be more vulnerable to extinction compared to other taxonomic groups, based on the principles of biodiversity loss discussed in the chapter.

Careful analysis of extinction records shows that extinctions are not random across taxa — some groups are more vulnerable; amphibians are a prominent example, with 32 per cent of all amphibian species currently facing extinction threats.
Amphibians are particularly sensitive to habitat loss and fragmentation because they require both aquatic and terrestrial habitats and have limited dispersal ability, making them highly susceptible when habitats are broken up.
Amphibians have permeable skin that makes them vulnerable to pollution, pesticides and chemical contamination of water bodies — indirect consequences of habitat degradation beyond outright destruction.
Climate change alters moisture and temperature regimes, directly threatening amphibian reproduction and survival in ways that affect them more severely than animals with more controlled water-retaining body systems.
Co-extinction vulnerability is also higher for amphibians since many are hosts to unique parasites and in ecological networks with specific predators and prey; their decline cascades into broader biodiversity impacts, demonstrating how the Evil Quartet compounds vulnerability for sensitive taxa.

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Medium

Question 10

Long Form

Discuss the broadly utilitarian argument for biodiversity conservation, with specific examples of ecosystem services.

The broadly utilitarian argument states that biodiversity plays a major role in ecosystem services — functions and benefits provided by natural ecosystems that sustain all life, including human civilisation.
The Amazon forest, through photosynthesis, produces an estimated 20 per cent of the total oxygen in Earth's atmosphere — a service whose economic value can be estimated only by the cost of artificially producing that oxygen.
Pollination is another critical service: pollinators including bees, bumblebees, birds and bats enable plants to produce fruits and seeds; without them, agricultural systems would collapse and food security would be severely threatened.
Biodiversity also provides flood control, pest and disease regulation, climate moderation, and soil formation — intangible services that maintain the conditions necessary for human life but are rarely given economic value in markets.
Beyond measurable services, biodiversity provides aesthetic pleasures — walking through forests, observing wildflowers, listening to birdsong — enriching human lives in ways that cannot be assigned a price, making them no less important.

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Chapter 13: Biodiversity and Conservation | Long Questions

Analyse the three hypotheses proposed to explain why the tropics show the greatest levels of species richness.

Compare and contrast in situ and ex situ conservation strategies with suitable examples from India.

Discuss the four causes of biodiversity loss known as the 'Evil Quartet' with examples.

Explain the three arguments for biodiversity conservation and assess their relative importance.

Explain the species-area relationship discovered by Alexander von Humboldt and discuss the significance of different Z values.

Evaluate the role of biodiversity in ecosystem functioning using David Tilman's findings and Paul Ehrlich's analogy.

Discuss the current state of global and Indian biodiversity loss, including key statistics on threatened species and the rate of extinction.

How do ecologists estimate global species richness? Discuss the limitations of current estimates and India's undiscovered species.

Analyse why amphibians appear to be more vulnerable to extinction compared to other taxonomic groups, based on the principles of biodiversity loss discussed in the chapter.

Discuss the broadly utilitarian argument for biodiversity conservation, with specific examples of ecosystem services.

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