Bacteria consist of
single cells. They are much smaller than animal or plant cells.
These cells have several similarities with cells of (green) plants and animals, but lots of differences, which is why they are put into a
kingdom of their own.
On the outside of the cell is a cell wall, but it is
not usually made of cellulose.
Inside this is a membrane enclosing the cytoplasm.
The genetic material is
not enclosed in a nuclear membrane like
higher plants and animals. The main genetic material is DNA, in a
diffuse blob, loose in the cytoplasm. Also in the cytoplasm there may be other loops of DNA which are called plasmids. This plasmid DNA is likely to contain
genes for other characteristics.
There are no mitochondria in bacterial cells. In fact they are about the same size as one another.
Likewise, there are no
chloroplasts in bacterial cells.
Bacterial cells do contain ribosomes, but they are slightly smaller than ribosomes in animal and plant cells.
Approximate sizes:
in micrometres (µm)
also known as microns
[1µm = 0.001mm = 0.000001m (10
-6m)]
| cell/component |
size / µm |
| E. coli cell length |
2 |
| E. coli cell width |
0.5 |
| Staphylococcus aureus cell diameter |
0.6 (600nm) |
| bacterial ribosome |
0.020 (20nm) |
Going down another 1000 ×
Another unit - the
nanometer - is often used to describe lengths of structures seen with the electron microscope.
[1nm = 0.001 µm = 0.000001mm = 0.000000001m (10
-9m)]
What you should know
A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall;
the genes are not in a distinct nucleus;
some of the genes are located in circular structures called plasmids.
Notes on words:
Bacterium is singular, bacteria plural.
Bacterial is an adjective, meaning to do with bacteria.
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