Distinguish obligate parasite from facultative parasites.

Obligate parasite completely depends on the host for survival. E.g. Clamydia is an example of obligate parasite as it depends on the eukaryotic cell for nourishment.

Facultative parasite does not depend on the host throughout its life cycle. E.g. Strongyloides stercoralis is a roundworm that can cause a disease strongyloidiasis but can also be found free-living.