Explain the concept of parasitism with various examples.

(N/A) Parasitism is a mode of life that ensures free lodging and meals,so it is not surprising that parasitism has evolved in so many taxonomic groups from plants to higher vertebrates.
Many parasites have evolved to be host-specific (they parasitize only a single species of host). In such cases,both host and parasite tend to co-evolve; that is,if the host evolves special mechanisms for rejecting or resisting the parasite,the parasite has to evolve mechanisms to counteract and neutralize them,in order to be successful with the same host species.
In accordance with their lifestyles,parasites have evolved special adaptations such as the loss of unnecessary sense organs,the presence of adhesive organs or suckers to cling to the host,loss of the digestive system,and high reproductive capacity. The life cycles of parasites are often complex,involving one or two intermediate hosts or vectors to facilitate parasitization of their primary host.
For example,the human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle. The malaria parasite needs a vector (mosquito) to spread to other hosts. The majority of parasites harm the host; they may reduce the survival,growth,and reproduction of the host and reduce its population density.
They might render the host physically weak,making them more vulnerable to predation. Do you believe that an ideal parasite should be able to thrive without harming its host?
Parasites that feed on the external surface of the host organism are called ectoparasites. The most familiar examples are lice on humans and ticks on dogs. Many marine fish are infested with ectoparasitic copepods. Cuscuta,a parasitic plant that is commonly found growing on hedge plants,has lost its chlorophyll and leaves in the course of evolution. It derives its nutrition from the host plant which it parasitizes. Female mosquitoes are not considered parasites,although they need our blood for reproduction.
In contrast,endoparasites are those that live inside the host's body at different sites (liver,kidney,lungs,red blood cells,etc.). The life cycles of endoparasites are more complex because of their extreme specialization. Their morphological and anatomical features are greatly simplified while emphasizing their reproductive potential.
Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them. During the course of evolution,the eggs of the parasitic bird have evolved to resemble the host's eggs in size and color to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest. Observe the cuckoo (koel) in your garden during the breeding season (spring to summer) and watch the process of brood parasitism.