Why must bacterial cells be first made ‘competent’ in r-DNA technology ? How is process carried ?

Question

(a) Why must bacterial cells be first made ‘competent’ in r-DNA technology ? How is process carried ?
(b) Name the method by which an alien DNA can be made to enter (i) plant cell; (ii) animal cell

Answer 1

(a) Since DNA is hydrophillic , it cannot pass through cell membrane hence bacterial
cells are made competent  by treatment with a specific concentration of a divalent cation,such as Ca++ which increases efficiency of entry of DNA through the pores of cell wall 
(b) i) plant cells - biolistic/ gene guns 
ii) animal cells- Micro injection