Definition of parasitism
Parasitology is a discipline that describes the relationships
(whatever these may be) between two organisms, i.e. the host organism
and the parasite. However, to define what is a host and what is a
parasite we have to define what exactly is parasitism.
When one organism gives shelter and food to another organism two
totally different situations may exist:
- Without any harm being done, or in the case where some
hosts may benefit from the presence of a parasite, in which case
we normally speak of:
- mutualism: a situation where two organisms live in
some contact and benefit from each others presence. They
exchange food or provide shelter or protection, but may still
be able to live an independent life.
- symbiosis: a situation where two organisms live in
close contact and benefit from each others presence. They have
become dependent upon each others presence and are unable to
survive independently.
- endosymbiosis: bacteria have invaded the cytoplasm
of a eukaryotic host cell. Host cell and bacterium have become
dependent upon each other. In the case large amounts of genetic
material have been moved from the bacterial genome to the
nucleus of the host an irreversible situation is reached which
led to the formation of:
- chloroplasts, photosynthetic organelles
that have originated from photosynthetic cyanobacteria
- mitochondria, organelles involved in
oxidative phosphorylation that have originated from the
alpha subdivision of the proteobacteria.
- With harm being done.
When one organism lives at the expense of its host we can distinct
several situations:
- viral infections
- bacterial infections
- parasitic diseases
NB: Normally a true parasite does not kill its host
Continue
Last updated: 29 September 2000.
created by :Fred
Opperdoes