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Biology · 2026 · 2 marks
Biotechnology : Principles and ProcessesProcesses of Recombinant DNA Technology2 marksUnderstandvery short answer
CBSE 2026 · Region 4 · Set 3 · Q20
Why and how can bacteria be made 'competent'?
Why and how can bacteria be made 'competent'?
Marking-scheme solution
• DNA is a hydrophilic molecule and it cannot pass through the cell
membrane hence the bacterial cell must be made competent to take up
DNA.
• The bacterial cells can be treated with a specific concentration of
divalent cation Ca2+ this increases the efficiency with which DNA enters the bacterium through the pores in the cell wall , followed by placing the cells with recombinant DNA on ice followed by placing them briefly at 420C (heat shock) and then putting them back on ice.
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.