1: The Life Cycle of Plasmodium). The vegetative, reproducing, feeding form of a protozoan is called a trophozoite (def). Under certain conditions, some protozoa produce a protective form called a cyst (def) that enable them to survive harsh environments.Cysts allow some pathogens to survive outside their host.rotozoa are unicellular eukaryotic microorganisms lacking a cell wall and belonging to the Kingdom Protista. Although there are nearly 20,000 species of protozoa, relatively few cause disease. Most inhabit soil and water.