Practice question

Parabasalid flagellates including Trichomonas vaginalis and Tritrichomonas foetus possess modified mitochondria adapted to anaerobic environments called hydrogenosomes, so named because they produce molecular hydrogen as metabolic end product. These double-membrane organelles lack genome, cristae, and respiratory chain, synthesizing ATP solely via substrate-level phosphorylation through pyruvate ferredoxin oxidoreductase and hydrogenase converting pyruvate to acetate, carbon dioxide, and hydrogen. Electron microscopy reveals granular matrix. Distinction from mitosomes which are further reduced to iron-sulfur biogenesis highlights progressive mitochondrial reduction along anaerobic gradient within Excavata lineage.