Which of the following methods can be used for making the bacterial cell “competent”?
(a) Treating with a specific concentration of divalent cation (Ca²⁺)
(b) Treating with a specific concentration of monovalent cation (K⁺)
(c ) Heat shock/ electric current of high voltage.

In order to force bacteria to take up the plasmid, the bacterial cells must first be made ‘competent’ to take up DNA. This is done by treating them with a specific concentration of a divalent cation, such as calcium, which increases the efficiency with which DNA enters the bacterium through pores in its cell wall. Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42⁰C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA. Heat shock/ electric current of high voltage can also be used for making bacterial cell competent.