What is meant by "competent cells" in bacterial transformation?

• A. Bacterial cells that are able to growth on non-selective media.
• B. Bacterial cells treated to increase their ability to take up foreign DNA, via chemical treatment or electroporation.
• C. Bacteria that have active restriction-modification systems.
• D. Bacteria that are naturally competent.

Answer: (B)

Competence is the ability of bacterial cells to take up extracellular DNA, which is what transformation relies on. In the laboratory, this ability is typically induced by making the cells temporarily permeable to DNA through chemical treatment or by using electroporation. Chemical methods, like treating cells with certain ions and then a heat shock, create conditions that allow DNA to cross the cell membrane. Electroporation uses a brief, high-voltage pulse to form pores in the membrane, letting DNA enter.

This option is the best because it directly describes how cells are prepared to acquire foreign DNA during transformation experiments. The other ideas don’t define competence in this context: growing on non-selective media is about growth conditions, not DNA uptake; active restriction-modification systems would actually defend against foreign DNA rather than enable uptake; and naturally competent bacteria can take up DNA without treatment, but the standard lab usage of “competent cells” refers to cells made competent by chemical or electrical methods.