Part (a) comprises a schematic representation of conjugation. Bacterial cells in blue are represented by a blue oval surrounded by a brown cell wall. Chromosomal DNA is represented as a purple squiggle. Plasmid DNA is represented as a green ring. The first part of the diagram shows two separate bacterial cells labelled donor and recipient. Both cells contain chromosomal DNA but only the donor contains the plasmid. In the next image the donor and recipient cells are connected by a tube which is coloured blue and surrounded by a brown cell wall. The tube is labelled pilus. The next images shows the plasmid DNA passing through the pilus. The final image shows the two bacterial cells still linked via a pilus however now both the donor and recipient cells contain plasmid DNA. Part (b) shows a scanning electron micrograph of two orange bacterial cells on a dark background. The cells are joined by two orange pili.

 2.2 Conjugation