Page 116 - Biology_F5

Comparative studies of natural groups of organisms

of one bacterium into two bacteria (Figure Sexual reproduction in bacteria
3.10). In this process, the dividing cell Sexual reproduction in bacteria is primitive
elongates and if the cell is spherical, the in the sense that it does not involve union
elongation is very much restricted. A rod- of gametes as commonly seen in other
shaped bacterium elongates to almost organisms, particularly the eukaryotes.
double its size. Then, the protoplasmic
FOR ONLINE READING ONLY
mass divides into two equal halves by a The reproduction simply involves
transverse wall or constriction. The cell combination of genetic material by the
division is preceded by the replication of process called genetic recombination.
DNA. The two daughter cells soon grow This process involves the primitive form
to maturity and divide further. of sexual reproduction called conjugation
(the transfer of DNA between two cells,
Cytoplasm which are in direct contact). One of the
Parental cell with its circular DNA two cells (male) donates while the other
DNA
Cell wall (female) receives genetic material. The
Cell replicates its DNA
ability to donate the genetic material is
The cytoplasm elongates, controlled by the bacterial gene found
separating the daughter DNA in a special type of plasmid called sex
molecules
Cross wall start to be formed factor, which also codes for the formation
of a small tubular structure called pilus,

Cross wall completely formed connecting the two bacterial cells.
Through this pilus, the genetic material is
Two daughter cells are injected into one or more recipient(s) at a
formed time. This kind of exchange is essential,
especially during unfavorable condition,

Figure 3.10: Bacterial reproduction by binary and they produce more resistant cells
fission (Figure 3.11).

Donor Recipient
Pilus

1. Formation of pilus 2. Pilus connects cells

4. Fragment of donor DNA 3. Donor DNA replicated by rolling
incorporated into recipient DNA cycle method and transferred
Figure 3.11: Sexual reproductions in bacteria

Form Five Student’s Book
109