The element is a clause if there is a subject and a verb, and it is a phrase if both of these parts of speech are not present. What comes after the introductory element is always an independent clause, or complete sentence, on its own, and the introductory element gives meaning to it.
A parasite is an organism that lives on or in a host organism and gets its food from or at the expense of its host. There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.
The third main type of symbiosis is parasitism. This is when one species benefits from the interaction and the other species is harmed. A parasite is an organism that lives on or within a host species. The host provides food and shelter to the parasite, but at a cost to the host itself.