Why must a cell be made 'competent' in biotechnology experiments?

a) The cell must be made competent in biotechnology experiments because DNA, being a hydrophilic molecule, cannot pass through the cell membrane. Hence, the cell should be made competent to accept the DNA molecule. Calcium ions play an important role in neutralizing the natural negative charges possessed by both DNA and the cell surface to avoid electrostatic repulsion between the two.
b) The biolistic gun has been developed to introduce rDNA into mainly plant cells by using a gene/particle gun. In this method, microscopic particles of gold/tungsten are coated with the DNA of interest and bombarded onto the cells.