- Parasitism
s It is a relationship between two living organisms of different species in which one organism called parasite obtains its food
directly from another living organism called host.
s The parasite is smaller as compared to its host. It spends a part or whole of its life on or in the body of the host.
Table: Characteristics of different types of parasite
Type of Parasite Characteristics
(i) (a) Ectoparasite
(b) EndoparasiteLive over the surface of host. e.g., Sucking lice, aphids
Live inside the host’s body, can be intracellular, body fluid parasite, gut parasite, e.g., Ascaris,
Trypanosoma.
(ii) (a) Temporary parasite
(b) Permanent parasiteLive in contact with host for only a part of their life e.g., bed bug, leech.
Live in contact with host throughout their life. They are transferred to new host as egg, cyst or
directly, e.g., Ascaris, Entamoeba, lice.
(iii) (a) Holoparasites(b) HemiparasitesParasites which are completely dependent on the host for all their requirements, e.g., Rafflesia,
Cuscuta.
Parasite which receive only a part of nourishment from the host while the rest is manufactured by
them, e.g., Viscum (Mistletoe).
(iv) Stem and root parasites Parasitic on plants and are in contact with the host plant either in the region of stem (e.g., Cuscuta,
Viscum, stem borer, lac insect) or root (e.g., Rafflesia, root nematodes).
(v) (a) Non-pathogenic
parasite
(b) Pathogenic parasiteParasite may not harm the host either because it deprives the host of only a fraction of food or is
dependent on the host for its dead tissues only, e.g., Entamoeba coli.
Parasites cause diseases in the host, e.g., Vibrio cholerae (cholera) Corynebacterium diphtheriae
(diphtheria).
(vi) Hyperparasite Parasite which lives on another parasite, e.g., some bacteriophages (bacterial viruses), bacterium
e.g., Pasteurella pestis in Xenopsylla cheopsis (Rat Flea) that is an ectoparasite of rat.
(vii) Brood parasitism Parasitic bird lays its eggs in the nest of its host and the host incubates them. During the course of
evolution, the eggs of the parasite bird have evolved to resemble the host’s egg in size and colour
to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest,
e.g., Cuckoo and crow.Anaerobic respiration in internal parasites.
Loss of certain organs (e.g., lice, fleas and bedbugs lack wings, Taenia
loses digestive system,).
Adhesive organs (e.g., suckers in leeches, tapeworms).
Excessive multiplication (parasites produce innumerable young ones).
Resistant cysts and eggs for safe transfer of their progeny to new
hosts.
Well developed and complicated reproductive organs.Adaptations for Parasitic Life- Amensalism
s Amensalism is an interaction between two living individuals
of different species in which an organism does not allow
other organism to grow or live near it.
s Inhibition is achieved through the secretion of chemicals
called allochemics.
s E.g., Pencillium does not allow the growth of Staphylococcus
bacterium. Trichoderma inhibits the growth of fungus
Aspergillus.- Commensalism
s It is the relationship between two living individuals of
different species in which one is benefitted while the other is
neither harmed nor benefitted except to a negligible extent.
s E.g., Sucker fish (Remora, Echeneis) attaches itself to the
under-surface of shark with the help of its dorsal fin which is
modified into holdfast.
s Epiphytes are small green plants which grow perched on
larger plants only for space, e.g., orchid, mosses, some ferns.
They are otherwise nutritionally independent. - Protocooperation
s Protocooperation is interaction between two living organisms
of different species in which both are mutually benefitted
but they can live without each other.