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Class 12th Biology 2012 Set1 Outside Delhi Board Paper Solution

Question 28

(a) Taking one example of habitat loss and fragmentation, explain how the two are responsible for biodiversity loss.
(b) Explain two different ways of biodiversity conservation.
(a) What depletes ozone in the stratosphere? How does this affect human life?
(b) Explain biomagnification of DDT in an aquatic food chain. How does it affect the bird population?

(a) Habitat loss and fragmentation is the most common factor for extinction. The example from the habitat loss is the tropical rain forests.6% of the earth land surface now comprises of the tropical rain forests which was earlier 14% and are destroyed very fast. The example for the fragmentation is the Amazon rain forest that leads to extinction of species which is being cut and cleared for soyabeans cultivation or for conversion to grasslands for raising beef cattle. This is the fragmentation of the land which leads to population declines.
(b) The two ways of biodiversity conservation are ex-situ and in-situ conservation.
Ex-situ conservation means literally, "off-site conservation". It is the process of protecting an endangered species of plant or animal outside its natural habitat; for example, by removing part of the population from a threatened habitat and placing it in a new location, which may be a wild area or within the care of humans. These were discovered as ‘biodiversity hotspots’ such as Western Ghats and Sri Lanka, Indo- Burma and Himalaya. In India, these have been conserved as 14 biosphere reserves, 90 national parks and 448 wildlife sanctuaries. In-situ conservation is on-site conservation or the conservation of genetic resources in natural populations of plant or animal species, such as forest genetic resources in natural populations of tree species. It is the process of protecting an endangered plant or animal species in its natural habitat, either by protecting or cleaning up the habitat itself, or by defending the species from predators. Zoological parks, botanical gardens and wildlife safari parks serve this purpose. Seeds of different genetic strains can be kept for long periods in seed banks.
(a) Ozone layer has been disrupted by the chlorofluorocarbons (CFCs).CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. The most likely health effects would be temporary and relatively harmless respiratory discomfort. Exposure to a direct jet of escaping CFC gas could cause local frostbite Encountering a huge amount of CFC's could lead to respiratory distress because they could displace the air in the local environment.
(b)Biomagnification refers to the increase in concentration of the toxic waste at successive tropic levels. Biomagnifications of DDT in an aquatic food chain causes the increase in concentration of DDT at successive tropic levels.
High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.
Fish eating birds (DDT 5ppm)
Large Fish (DDT 2ppm)
Small Fish (DDT 0.5ppm) Zooplankton(DDT 0.04ppm)
Water(DDT 0.003ppb)


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