Answer
· Commensalism
is
an interaction between two animal or plant species that habitually live together
in which one species (the commensal) benefits from the
association while the other is not significantly affected. For example, the
burrows of many marine worms contain commensals that
take advantage of the shelter provided but do not affect the
worm.
· Mutualism
is
an interaction between two species in which both species benefit. A well-known
example of mutualism is the association between termites and the specialized
protozoans that inhibit their guts. The protozoans, unlike the termites, are able to digest the
cellulose of the wood that the termites eat and release sugars that the termites
absorb. The termites benefit by being able to use the wood as a foodstuff, while
the protozoans are supplied with food and a suitable
environment.
Parasitism
is
an association in which one organism (the parasite) lives on (ectoparasitism) or in (endoparasitism) the body of another (the host), from which
it obtains its nutrients. Some parasites inflict comparatively little damage on
their host, but many cause characteristic diseases (these are, however, never
immediately fatal, as killing the host would destroy the parasite’s source of
food). Parasites are usually highly specialized for their way of life, which may
involve one host or several. The typically produce vast numbers of eggs, very
few of which survive to find their way to another suitable host. Obligate
parasites can only survive and reproduce as parasites; facultative parasites can
also live as saprotrophs. The parasites of human
include fleas and lice (which are ectoparasites),
various bacteria, protozoans, and fungi (endoparasites causing characteristic diseases), and
tapeworms, which lives in the gut.
Assignment submitted by S.M., Kang, E.S., Ong, T.W., Tan, K.Y., Ho. X.H., Wong 2011/2012 (IBM)
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