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.
There are 3 types of symbiosis: Parasitism is a relationship in which one organism - the host - is the source of food and/or shelter for another organism, the parasite. In this relationship, all of the benefits go to the parasite; the host is harmed by the relationship. An example is a human and a tapeworm living in the intestines.