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Biology · 2025 · 5 marks
Biotechnology and its ApplicationsBiotechnological Applications in Agriculture5 marksUnderstandlong answer
CBSE 2025 · Region 6 · Set 1 · Q31
(a) (i) Explain how some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans but do not kill the…
(a)(i)
Explain how some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans but do not kill the Bacillus.
(ii)
How is the above mechanism exploited for the production of Bt cotton plant by biotechnologists ?
OR
(b)(i)
Explain how the amplification of gene of interest is done using PCR.
(ii)
State two applications of the desired amplified fragment of DNA.
Marking-scheme solution
(i)
Bacillus thuringiensis forms Bt toxin protein which exist as inactive
protoxins hence bacteria are not killed
-once the insect ingests inactive protoxin, it gets converted to its active form due to
alkaline pH of the gut of larva which solubilise the crystals, activated toxin binds to surface of midgut epithelial cells, cause cell swelling and lysis and eventually death of insect
(ii)
Specific Bt toxin genes were isolated from Bacillus thuringiensis, and
expressed in cotton, when the cotton bollworm ingests plant part, it will not survive
(i)
– Denaturation, two strands of DNA are separated at high heat or temperature
Annealing of primer, two set of Primer binds to DNA
-Extension, Enzyme Taq polymerase extend the primer using the nucleotide
provided in the reaction and the genomic DNA as template
(ii)
The amplified fragments can now be used to ligate with a vector for further
cloning/ DNA fingerprinting, recombinant protein synthesis/ Diagnosis of diseases
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.