Bacterial cells have the capability of incorporating foreign naked DNA or deoxyribonucleic acid fragments from the environment or the exterior of the cell to the interior of the cell. This process is known as Transformation.
The bacterial cells which are able to undergo transformation are called Competent bacterial cells.
Some of the bacterial cells are naturally competent like<em> Bacillus subtilis, Streptocossus pneumoniae</em> while others like <em>Escherishia coli </em>need to be chemically treated to make them artificially competent.
In natural competence, the foreign DNA from the cell exterior is incorporated into the cell interior through specific protein complexes present in the plasma membrane of the bacterial cells.
In artificial competence, the negative charge on foreign DNA is masked by positively charged calcium ions (so that it is not repelled by the negative charge of the lipid bilayer of the bacterial cell plasma membrane) and then small pores are created in the lipid bilayer of the plasma membrane of the bacterial cells by giving a heat shock to the cells. This results in the uptake of the DNA by the bacterial cells.
Assume as what happens in a pot of water as it get heats.. hot becomes less dense, rises and cools, becoming more dense then sinks- that's called CONVECTION So D- is the right answer
