Obligate parasites are organisms that are unable to complete their life cycle without a suitable living host. Without a living host, the obligate parasite will fail to reproduce. Obligate parasitism is seen in a wide range of organisms, such as bacteria, viruses, animals, plants, and fungi. Examples of obligate parasitism are
(i) Plasmodium sp.: The genus Plasmodium contains unicellular eukaryotes such as P vivax and P falciparum. The parasite causes malaria in humans. Plasmodium sps. are obligate parasites of mosquitoes and humans.
(ii) Viruses: All the viruses are obligate parasites. Viruses usually lack metabolic machinery to synthesize proteins or energy production. Due to which viruses always depend on host cells to carry out their growth and reproduction.