Bacteria are microscopic, prokaryotic organisms that lack nuclei in their cells. They vary in size from 0.2-2 micrometers in diameter and 0.5-5 micrometers in length, though some large bacteria can be seen with the naked eye. Bacteria come in four basic shapes - bacillus (rod-like), coccus (spherical or ovoid), vibrio (comma-shaped), and spirilla (spiral or helical). They can exist as single cells or in various arrangements like chains or clusters depending on how they divide and remain attached after division. Their small size gives bacteria a large surface area to volume ratio, allowing for rapid nutrient absorption and waste removal.

1. STRUCTURE OF BACTERIAL CELL
ANKIT ALANKAR
CHANAKYA EDUCATION HUB

2. BACTERIA
 Bacteria (eubacteria) are microscopic , relatively simple,
prokaryotic organisms whose cells lack a nucleus.
Prokaryotes can be distinguished from eukaryotes in terms of
their cell structure & molecular make up.
Prokaryotic cells are morphologically simpler then eukaryotes
cells.
Many structure are common to both cell types , some are unique
to prokaryotes .
Most prokaryotes lack extensive , complex , internal membrane
systems.

3. SIZE OF BACTERIAL CELL
 Bacteria range in size from 0.2 – 2 micrometers in diameters
& 0.5 – 5 micrometers in length.
A few species for example ,
1. Thiomargarita namibiensis
2. Epulopiscium fishelsoni
are very large and visible to the unaided eye .
The rod shape E. fishelsoni is about 600 micrometers in length
& 75 micrometers in diameters .
The smallest known bacteria are members of the genus
Mycoplasma (about 0.3 micrometers in diameter).

4.  Most bacteria are very small size . Because of their small size ,
bacteria have a large surface area -to- volume ratio.
The large surface area -to- volume ratio of bacteria also means
that no internal part of the cell is very far from the surface & the
nutrients can easily and quickly reach all parts of the cell. It allow
rapid uptake and intercellular distribution of nutrients and
excretion of wastes . At low surface area-to-volume ratio, the
diffusion of nutrients and waste products across the cell
membrane limit the rate at which microbial metabolism occurs,
making the cell less evolutionarily fit.

5. SHAPE OF BACTERIAL CELLS
 The four basic shape of bacteria are :-
1. bacillus (rod like)
2. coccus (spherical or ovoid)
3. vibrio (comma shaped)
4. spirilla (spiral or helical shaped)
the term ‘Bacillus’ has two meaning . Bacillus refers to a bacterial
shape as well as genus . when capitalized and italicized , it refers to
a specific genus. For example , bacillus anthracis, the causative
agent of anthrax.

6. ARRANGEMENT OF BACTERIAL CELLS
 When cocci divide, cell can remain attached to one another .
Cocci that remain in pairs after dividing are called diplococci,
those that divide and remain attached in chain like patterns are
called streptococci .
Some cocci divided in two planes and remain in groups of four
, forming squares are knows as tetrads.
Those that divided in three planes and remain attached in
cubelike group of eight are called sarcinae.
Those that divided in multiple planes and from grapelike
clusters are called staphlylococci.

7.  Most bacilli appear as single rods.
Diplobacilli appear in pairs after division , and strptobacilli occur in
chains .
Bacteria that look like curved rods are called vibrios.
Spirilla have a helical shape and fairly rigid bodies. Another group of
spirals are helical and flexible ; they called spirochetes.
Most bacteria maintain a single shape (monomorphic ).
Some bacteria like Corynobacterium, have many shapes , and lack a
single , characteristic shape . These bacteria are called pleomorphic .
 The modern definition of pleomorphism in the references of
bacteriology is based on variation of shape of the cell, rather than a
change of shape.