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Biology · 2025 · 5 marks
Biotechnology and its ApplicationsBiotechnological Applications in Agriculture5 marksUnderstandlong answer
CBSE 2025 · Region 5 · Set 2 · Q32
(a) (i) Explain why the insecticidal protein producing by Bacillus thuringiensis does not kill the bacteria itself. (ii) How has man exploited this…
(i)
Explain why the insecticidal protein producing by Bacillus thuringiensis does not kill the bacteria itself.
(ii)
How has man exploited this protein to produce cotton bollworm resistant Bt cotton plant?
(i)
Identify the selectable markers labelled as 'a' and 'b' in the given diagram of E. coli vector.
(ii)
How is coding sequence of enzyme $\displaystyle \beta$-galactosidase considered a better marker than the ones identified by you in the diagram ? Explain.
(iii)
List any two uses of cloning vector in biotechnology.
Marking-scheme solution
(i)
Bacillus thuringiensis produces protein crystals during a particular phase of their
growth, which contain a toxic insecticidal protein, Bt toxin protein exist as inactive protoxins, to get it activated alkaline pH is not available in the bacteria.
(ii)
The proteins encoded by genes Cry IAc and Cry IIAb controls the cotton bollworms,
these specific Bt genes were isolated from Bacillus thuringiensis and incorporated into the cotton plants.
(i)
‘a’ - ampR and ‘b’ - tetR
(ii)
Enzyme β-galactosidase helps to differentiate recombinants from non-recombinants on
the basis of their ability to produce colours in the presence of chromogenic substrate
Selection of recombinants due to inactivation of antibiotic resistance is cumbersome
because it involves simultaneous plating of two plates having different antibiotics.
(iii)
Cloning vectors are used to make multiple copies of the desired DNA / gene
They are used to transfer gene of interest to the host cell
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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.