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Biodiversity and Conservation — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYBiodiversity and Conservation4 Marks
Question
Explain loss of biodiversity.
✓

Answer

→ The biological wealth of our planet has been declining rapidly and the accusing finger is clearly pointing to human activities.
→ 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 (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
→Some examples of recent extinctions include the
→ Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller's Sea Cow (Russia) and three subspecies (Bali, Javan, Caspian) of tiger.
→ The last twenty years alone have witnessed the disappearance of 27 species.
→ Careful analysis of records shows that extinctions across taxa are not random; some groups like amphibians appear to be more vulnerable to extinction.
→ Adding to the grim scenario of extinctions is the fact that more than 15,500 species world- wide are facing the threat of extinction.
→ Presently, 12 per cent of all bird species, 23 per cent of all mammal species, 32 per cent of all amphibian species and 31per cent of all gymnosperm species in the world face the threat of extinction.
→ From a study of the history of life on earth through fossil records, shows 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 long the period (> 3 billion years) since the origin and diversification of life on earth there were five episodes of mass extinction of species.
→ 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.

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Restriction endonuclease was isolated for the first ti me by W. Arb er in 1962 in bacteria. Restriction endonucleases cut the DNA duplex at specific points therefore they are also called as molecular scissors or biological scissors. Three types of restriction endonucleases are Type I, Type II and Type III but only Type II restriction endonucleases are used in recombinant DNA technology. Restriction endonuclease EcoR I recognises the base sequence GAATTC in DNA duplex and cut strands between G and A.

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  1. $\ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  2. $ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  3. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \uparrow$

  4. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

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