Page 4 - 11-Bio-6 Kingdom prokaryotae

6. Kingdom prokaryotae(Monera) eLearn.Punjab

STRUCTURE OF BACTERIA

All bacterial cells invariably have a cell membrane, cytoplasm, ribosome, and chromatin bodies.
The majority have a cell wall, which gives shape to the bacterial cell. Specific structures like capsule,
slime, flagella, pili, fimbriae and granules are not found in all bacteria (refer to Fig. 4.17).

Size

Bacteria range in size from about 0.1 to 600 nm over a single dimension. Bacteria vary in size

as much as in shape. The smallest (e.g., some members of Recently a huge bacterium has been

the genus Mycoplasma) are about 100 to 200 nm in diameter, discovered in the intestine of the brown
surgeonfish, Acanthurus nigrofuscus.
approximately the size of the largest viruses (poxviruses) Epulopiscium fishelsoni grows as large as

Escherichia coli, a bacillus of about average size, is 1.1 to 1.5 600 nm by 80 nm, a little smaller than a
printed hyphen. It is now clear that a few
nm wide by 2.0 to 6.0 nm long. Some spirochetes occasionally bacteria are much larger than the average

reach 500 nm in length whereas Staphylococci and Streptococci eukaryotic cell.

are 0.75 - 1.25n in diameter.

Shape of Bacteria

On the basis of general shape, bacteria are classified into three categories. These shapes are known
as cocci, bacilli and spiral .Although most of the bacterial species have fairly constant characteristic
cell shape, yet some cells are pleomorphic and they can exist in a variety of shapes.

Exceptions to the above shapes are
trichome forming, sheathed, stalked,
square, starshaped, spindle-shaped,
lobed and filamentous bacteria.

4 V: 1.1