Practice question

Microsporidia are obligate intracellular parasites unable to grow outside host cytoplasm, depending entirely on host ATP and metabolites due to extreme genome compaction lacking tricarboxylic acid cycle genes and electron transport chain components. Spores injected via polar tube into host cells develop as meronts proliferating and sporonts forming spores. Free-living saprotrophs and photosynthetic fungi nonexistent in this phylum; facultative parasites can grow independently, which microsporidia cannot due to loss. They infect wide range hosts from protists insects to vertebrates causing chronic diseases especially in immunocompromised humans. Obligate intracellular lifestyle defines niche.