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Biology · 2023 · 5 marks
Biotechnology : Principles and ProcessesProcesses of Recombinant DNA Technology5 marksUnderstandlong answer
CBSE 2023 · Region 3 · Set 1 · Q31
(a) Answer the following questions with respect to recombinant DNA technology: (i) Why is plasmid considered to be an important tool in rDNA…
Answer the following questions with respect to recombinant DNA technology :
(i)
Why is plasmid considered to be an important tool in rDNA technology ? From where can plasmids be isolated ? (Any two sources)
(ii)
Explain the role of 'ori' and selectable marker in a cloning vector.
(iii)
"r-DNA technology cannot proceed without restriction endonuclease." Justify.
Answer the following questions based on Bt-crops :
(i)
Why do farmers prefer to grow Bt cotton crop than genetically unmodified cotton crops ?
(ii)
Name any two insects that are killed by Bt toxin.
(iii)
Explain the mechanism by which Bt toxin kills the insects but not the bacterium which possesses the toxin.
Marking-scheme solution
(i)
Can act as vector/can self-replicate to form multiple copies/ have selectable markers/ small in size will facilitate insertion / presence of 'Ori'
E. coli, Agrobacterium tumefaciens, Salmonella typhi, Bacteria
(ii)
'Ori' - this is a sequence from where replication starts / any piece of DNA when linked to this sequence can be made to replicate with in the host cells controls copy number of linked DNA.
Selectable marker helps in identifying and eliminating non-transformants, and selectively permitting the growth of transformants during recombinant DNA technology.
(iii)
Restriction endonuclease identifies a specific palindromic sequence of DNA and cut the DNA at the specific sites in both the host as well in desired/foreign DNA, thereby creates "sticky ends" facilitating ligation to form a recombinant DNA.
(i)
Bt cotton crop is pest resistant/Insect resistant/ with increase productivity
(ii)
Cotton bollworms/corn borer/tobacco budworm/army worm/coleopterans (beetles)/dipterans (flies, mosquitoes)
(iii)
BT toxin protein exists as an inactive protoxin in the bacterium, but once the insect ingests this toxin it is converted into an active form, due to the alkaline pH of the gut, which solubilizes inactive crystals of toxic insecticide the activated toxin binds to the surface of the midgut epithelial cells of the insect, creates pores, that cause cell swelling and lysis and eventually the death of the insect.
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CBSE Class 12 Biology past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.