AP BIOLOGY

Detailed explanation-1: -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. Entamoeba histolytica is a protozoan. A microscope is necessary to view this parasite.

Detailed explanation-2: -Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat. Viruses may be viewed as mobile genetic elements, most probably of cellular origin and characterized by a long co-evolution of virus and host.

Detailed explanation-3: -In contrast, parasites that live inside their hosts are known as endoparasites (Figure 2B).

Detailed explanation-4: -Parasitism is a kind of symbiosis, a close and persistent long-term biological interaction between a parasite and its host. Unlike saprotrophs, parasites feed on living hosts, though some parasitic fungi, for instance, may continue to feed on hosts they have killed.