Explain parasitism and co-evolution with the help of one example of each.

Hint: Symbiosis is the term, which is used to describe the relation or interaction between the two dissimilar organisms in the ecosystem. Generally, there are five types of relations, which include mutualism, parasitism, predation, commensalism and competition.

Complete answer:
Parasitism: In the ecosystem, parasitism is the symbiotic relationship between the two organisms, where one is the host and the other is the parasite, in this relation parasite may cause harm to the host.

Generally, a parasite is of two types, they are:
> Ectoparasite: where parasite lives on the surface of the host, most of the Ectoparasites does not cause unnecessary harm, but sometimes these also have chance to cause or to spread diseases, example for the ectoparasite is Louse which lives on the head of humans, where they feed on human blood, most of them won’t cause any deadly disease.
Endoparasite: where the parasite lives inside the host organism, and they in turn classified as intracellular and intercellular endoparasites, one of the examples for endoparasite is Plasmodium vivax it is the bacterial parasite which usually spread by the mosquito where inside the mosquito it does not cause any effect, while it enters the human blood, it feeds on the human and it undergoes its life cycle in the human but in return, it causes the fever, infection and other side effects to the humans.

> Coevolution: It is the process where there are reciprocal evolutionary changes in the pair of species or the group of species that interact with each other, in this process the habit of species may show the selective interactive pressure on other species.
The relation that comes under the co-evolution is mutualism, predator-prey, host-parasite.

Examples for this are flowers and the pollinators like insects, birds, etc. Usually, insects feed on flowers for nectar, whereas the flowers use the insects for pollination by attaching the pollen grains to the body of insects so that if they feed on other plants, pollination takes place, in these process, flowers are evolving to attract the insects like having bright color flowers, strips and releasing certain scents, etc. While the insects and birds are adapting to have the pollen in certain parts and easily accessible for pollination in other parts, this is the classic example of the co-evolution.

Note: In the case of parasitism, the host gets harmed by the parasite and the parasite gets benefits from the host, whereas in the co-evolution, in the prospect of mutualism, both are adapted and develops some special features and evolves to the new things.