NCERT Exemplar: Biodiversity & its Conservation - 2 | Biology Class 12 - NEET PDF Download

SHORT ANSWER TYPE QUESTIONS

Q.1. How is the presently occurring species extinction different from the earlier mass extinctions?
Ans. Species extinction occurring at present is due to anthropogenic causes where as the earlier extinction was due to natural causes.

Q.2. Of the four major causes for the loss of biodiversity (Alien species invasion, habitat loss and fragmentation, over-exploitation and co-extinctions which according to you is the major cause for the loss of biodiversity? Give reasons in support.
Ans. Habitat loss and fragmentation is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests. Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent. They are being destroyed fast. By the time you finish reading this chapter, 1000 more hectares of rain forest would have been lost. The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’) harbouring probably millions of species is being cut and cleared for cultivating soyabeans or for conversion to grasslands for raising beef cattle.

Q.3. Discuss one example, based on your day-to-day observations, showing how loss of one species may lead to the extinction of another.
Ans. In case a species (x) becomes extinct, the plant and animal species (M, N, O, Z) associated within an obligatory way also become extinct. For example.
(i) When a fish species which is a host for a number of parasites becomes extinct the parasite species which are uniquely dependent on the host fish will also become extinct.
(ii) The insects may be polyphagous (feed on more than one plant species) or monophagous (feed on only one particular plant species) in nature. The monophagous insect species are valuable and may become extinct if the plant species upon which it feeds becomes extinct.

Q.4. A species-area curve is drawn by plotting the number of species against the area. How is it that when a very large area is considered the slope is steeper than that for smaller areas?
Ans. Ecologists have discovered that the value of Z (slope of the line) lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region (whether it is the plants in Britain, birds in California or molluscs in New York state, the slopes of the regression line are amazingly similar). But, if you analyse the species-area relationships among very large areas like the entire continents, you will find that the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2). For example, for frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents, the slope is found to be 1.15.

Q.5. Is it possible that productivity and diversity of a natural community remain constant over a time period of, say one hundred years?
Ans. Yes, productivity and diversity of a natural climax community remain constant over a time period.

Q.6. There is greater biodiversity in tropical /subtropical regions than in temperate region. Explain.
Ans. 
(a) Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification.
(b) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
(c) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.

Q.7. Why are the conventional methods not suitable for the assessment of biodiversity of bacteria?
Ans. Many bacteria are not culturable under normal conditions in the laboratory. This becomes a problem in studying their morphological, biochemical and other characterizations which are useful for their assessment.

Q.8. What criteria should one use in categorizing a species as threatened?
Ans. 
(i) Extinction risk : Number of the individuals of the species are declining at an alarming pace.
(ii) Predation pressure
(iii) Habitat loss and fragmentation

Q.9. What could be the possible explanation for greater vulnerability of amphibians to extinction as compared to other animal groups?
Ans. Amphibians live in terrestrial habitat but for sexual reproduction they depend on aquatic habitat. Habitat loss affects the amphibians more greatly than other animal groups because it requires both the habitat for its survival.

Q.10. How do scientists extrapolate the total number of species on Earth?
Ans. Scientists make a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the total number of species on earth.

Q.11. Humans benefit from diversity of life. Give two examples.
Ans. Humans derive countless direct economic benefits from nature. For example:

1. Food (cereals, pulses, fruits)
2. Firewood
3. Fibre
4. Construction material .
5. Industrial products (tannins, lubricants, dyes, resins, perfumes)
6. Products of medicinal importance.

Q.12. List any two major causes other than anthropogenic causes of the loss of biodiversity.
Ans. 
(i) Volcanic storms
(ii) Co-extinctions

Q.13. What is an endangered species? Give an example of an endangered plant and animal species each?
Ans. Endangered (ER): It is facing a high risk of extinction in the wild in the near future if conservation measures are not promptly taken.
Example: Red panda (Ailurus fulgens), Drosera indica.

Q.14. What are sacred groves and their role in biodiversity conservation?
Ans. In many cultures, tracts of forest were set aside, and all the trees and wildlife within were venerated and given total protection. Such sacred groves are found in Khasi and Jaintia Hills in Meghalaya, Aravalli Hills of Rajasthan, Western Ghat regions of Karnataka and Maharashtra and the Sarguja. Chanda and Bastar areas of Madhya Pradesh. In Meghalaya, the sacred groves are the last refuges for a large number of rare and threatened plants.

Q.15. Suggest a place where one can go to study coral reefs, mangrove vegetation and estuaries.
Ans. Coral reefs—Andaman and Nicobar Mangrove vegetation—West Bengal Estuaries—Kerala, Karnataka, Tamil Nadu

Q.16. Is it true that there is more solar energy available in the tropics? Explain briefly.
Ans. As one moves from the equator to the polar regions, the length of the day decreases and the length of the night increases. The length of day and night are the same at the equator.

Q.17. What is co-extinction? Explain with a suitable example?
Ans. When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of a coevolved plant-pollinator mutualism where extinction of one invariably leads to the extinction of the other.

LONG ANSWER QUESTIONS

Q.1. Elaborate how invasion by an alien species reduces the species diversity of an area.
Ans. Some possible explanations are that the alien species may be:

1. Vigorously growing and compete with the natural plants for minerals, water etc. The less vigorous local species may be eliminated.
2. Natural pests and predators of the alien species may not be present in the introduced area-leading to proliferation in their number.
3. The introduced species may harm the local species by production of chemicals (Amensalism).
4. The alien species by proliferation may make conditions unfavourable for the growth of local native plants. (Example: Eichhomia)

Q.2. How can you, as an individual, prevent the loss of biodiversity?
Ans. The loss of biodiversity can be prevented by: 

1.  Practise of recycling waste paper etc.
2. Judicious exploitation of medicinal and commercial plants and animals.
3.  Generating awareness among the public on the importance of biodiversity, conversation through skits, screening of films, lectures etc.

Teaching people how to reduce green house gases emissions, through alternate eco friendly green technologies like use of solar energy, wind energy, biogas, vermicompost, organic farming etc.

Q.3. Can you think of a scientific explanation, besides analogy used by Paul Ehrlich, for the direct relationship between diversity and stability of an ecosystem?
Ans. David Tilman’s long-term ecosystem experiments using outdoor plots provide some tentative answers. Tilman found that plots with more species showed less year-to-year variation in total biomass. He also showed that in his experiments, increased diversity contributed to higher productivity. Although, we may not understand completely how species richness contributes to the well-being of an ecosystem, we know enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet.

Q.4. Though the conflict between humans and wildlife started with the evolution of man, the intensity of conflict has increased due to the activities of modern man. Justify your answer with suitable examples.
Ans.  From a study of the history of life on earth through fossil records, we leam that large-scale loss of species like the one we are currently witnessing have also happened earlier, even before humans appeared on the scene. During the long period (> 3 billion years) since the origin and diversification of life on earth there were five episodes of mass extinction of species. How is the ‘ Sixth Extinction’ presently in progress different from the previous episodes? The difference is in the rates; the current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times and our activities are responsible for the faster rates. Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years. The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than 2,000 species of native birds. The IUCN Red List (2004) documents the extinction of 784 species. The last twenty years alone have witnessed the disappearance of 27 species.

Q.5. What is an ecosystem service? List any four important ecosystem services provided by the natural ecosystems. Are you in favour or against levying a charge on the service provided by the ecosystem?
Ans. The products of ecosystem processes are named as ecosystem services, for example, healthy forest ecosystems purify air and water, mitigate droughts and floods, cycle nutrients, generate fertile soils, provide wildlife habitat, maintain biodiversity, pollinate crops, provide storage site for carbon and also provide aesthetic, cultural and spiritual values. Though value of such services of biodiversity is difficult to determine, it seems reasonable to think that biodiversity should carry a hefty price tag. Robert Constanza and his colleagues have very recently tried to put price tags on nature’s life-support services. Researchers have put an average price tag of US $ 33 trillion a year on these fundamental ecosystems services, which are largely taken for granted because they are free. This is nearly twice the value of the global gross national product GNP which is (US $ 18 trillion).

Q.6. Describe the consumptive use value of biodiversity as food, drugs and medicines, fuel and fiber with suitable examples.
Ans. The direct use values where the biodiversity products can be harvested and consumed directly are called consumptive use value of biodiversity, 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 currently sold in the market worldwide are derived from plants and 25,000 species of plants contribute to the traditional medicines used by native peoples around the world.

Q.7. Species diversity decreases as we move away from the equator towards the poles. What could be the possible reasons?
Ans. In general, species diversity decreases as we move away from the equator towards the poles. The possible reason could be as follows:

1. Temperature decreases as we move away from the equator towards the poles.
2. The intensity of sun light decreases as we move away from the equator towards the poles and hence productivity.
3. In polar regions the temperature is very low so most of the organisms cannot survive in that habitat.

Q.8. Explain briefly the ‘rivet popper hypothesis’ of Paul Ehrlich.
Ans. Paul Ehrlich proposed Rivet popper hypothesis to show the effect of biodiversity loss on the ecosystem. An airplane (ecosystem) has thousands of rivets. Popping of rivets (causing a species to become extinct) by passenger may not affect flight safety (Proper functioning of the ecosystem) in the beginning but the plane will become dangerously weak over a period of time. Removal of a rivet of a critical part like wing (key species that derive major ecosystem functions) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or window inside the plane.

Q.9. The relation between species richness and area for a wide variety of taxa turns out to be a rectangular hyperbola. Give a brief explanation.
Ans. During his pioneering and extensive explorations in the wilderness of South American jungles, the great German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola.