Q.4. What is adaptation? Explain with reference to the structure and life history of Fasciola hepatica.
Or
Describe parasitic adaptations of Fasciola hepatica.
Ans.4. Parasitism
It is an intimate relationship between organisms of two different species in which one benefits and the other is harmed.
Parasitic Adaptations in Fasciola
Parasitic Adaptations
The parasitic adaptations in the organisation and life-history of a parasite can be defined as the profound changes and modifications occurring in pursuit of successful parasitism so that the parasite is fully adapted inside the body of the host. Fasciola (liver-fluke) is an endoparasite in the liver of sheep. It has undergone modifications under the stress of the parasitic mode of life which can be discussed under the following heads :
A. Morphological Adaptations
1. Thin, flattened and somewhat triangular body enables liver fluke to live in narrow bile passages and minimizes the danger of injury.
2. Oral or anterior sucker and ventral or posterior sucker are organs for attachment to the host.
3. External organisation is very simple with no distinction into head, trunk and tail without any appendages, since these might prove harmful in the endoparasitic mode.
B. Anatomical Modifications
1. Body is devoid of cilia in adult stage but is protected by a thick layer of cuticle to save it from the effect of chemicals from host body. For the same purpose the skin is supplemented by spicules.
2. The thickening of cuticle in the oral and ventral regions leads to the formation of two suckers.
3. The locomotory organs are absent in the adult Fasciola because it need not search for food and safety.
4. The digestive system is incomplete. The pharynx is muscular and suctorial, adapted to suck the nutrient.
5. The intestine is highly branched to distribute the digested food to various parts of the body. Thus it has taken over the work of circulatory system.
6. Since plenty of readymade and pre-digested food is available to the animal, the anus is absent.
7. The circulatory system and the organs of respiration are absent. The respiration is of anaerobic type, a remarkable adaptation to endoparasitic mode of existence, as no free oxygen is available in host body.
8. To compensate the loss of circulatory system, excretory system is highly developed. It consists of extensively branched system of excretory ducts, ending into flame cells. This facilitates the collection of excretory products from the interior of body.
9. Nervous system is poorly developed and sense organs are lacking since the parasite does not react with the external environment, and there are least changes inside the body of host.
10 Reproductive organs are extensively developed. The highly branched ovary and testes are capable of producing large number of gametes. Bisexuality offers full chances of fertilisation.
C. Physiological Adaptations
1. Parasite is well adapted to osmotic concentration of the bile in which it lives.
2. Osmoregulation is not needed because the osmotic concentration of body fluids of Fasciola is equal to that of host’s bile.
D. Modifications in Life-History
1. Production of very large number of eggs (about 10 million) to overcome the risk during dispersal.
2. Eggs are shelled and operculated so that they cannot be easily destroyed.
3. Introduction of a secondary host in the life-history to ensure the dispersal of race.
4. Multiplication of the larval forms by paedogenesis (asexual multiplication of larvae from the germ cells of larvae).
5. Miracidium is a free-swimming and ciliated larva as it is to search for a new host. The cercaria gets encysted when out of the body of the secondary host which ensures protection from external effects.
BSc 1st Year Lower Non-chordates Fasciola Hepatica Sample Model Practice Question Answer Papers
BSc 1st Year Sample Model Practice Mock Test Question Answer Papers