Most micro-organisms are harmless and many play an essential role in recycling nutrients in the environment (e.g. nitrogen and carboncycle). Some can cause diseases (pathogens); others are useful (produce antibodies)
A pathogen is a disease causing micro-organisms
Examples are:
Bacteria
Viruses
Fungi
Bacteria
It is believed that some bacteria are the oldest forms of life
A bacteria cell contains cytoplasm, cell membrane and cell wall
Nonucleus, only a stand of circular DNA
Bacteria reproduce by dividing in two or form clones
Viruses
Viruses are smaller than bacteria
They contain a protein coatsurrounding a number of genes
They can only reproduce in a host cell
Producing new viruses destroys the host cell as the new viruses are free to attack other cells
Communicable diseases
This means by which bacteria, viruses and fungi can be spread are as follows:
