 The apicoplast organelle in these organisms is believed to have come from an endosymbiotic event in which an ancestral protozoan engulfed an algal cell.These apicoplasts contain plant-like FNRs that the protozoan uses to generate reduced ferredoxin, which is then used as a reductant in essential biosynthetic pathways.FNRs from two major parasites affecting humans, "Plasmodium falciparum", which causes malaria, and "Toxoplasma gondii", which causes toxoplasmosis, have been sequenced.