In what life cycle stage is Trophozoite the only morphological form present?

The trophozoite stage is characterized by the active, motile form of certain protozoa. In the case of Pentatrichomonas hominis, the trophozoite is indeed the only morphological form present throughout its life cycle. This organism does not form cysts, which are dormant stages seen in some other protozoa, meaning that it exists only in its active form in the host's intestines.

For other organisms in the choices, they utilize different life stages. For example, Giardia lamblia can exist as both trophozoite and cyst forms, where the cyst provides a resistant structure for survival outside the host. Similarly, Entamoeba histolytica exists as trophozoites in the human intestine but forms cysts when passing through the gastrointestinal tract to survive external conditions. Trichomonas vaginalis is also a trophozoite but does not differentiate into a cystic form like other protozoa.

Thus, Pentatrichomonas hominis specifically showcases the trophozoite as its sole form, making it unique among these options.