Practice question

Polar tube represents unique invasion organelle exclusively characteristic of Microsporidia essential for host cell entry. Coiled inside spore in resting state as highly pressurized spring, upon stimuli of pH shift, osmotic pressure and calcium influx, tube rapidly everts reaching up to fifty microns length puncturing host plasma membrane acting as conduit for sporoplasm injection directly into host cytosol, evading extracellular immune surveillance. Consists of polar tube proteins PTP1-3 providing elasticity and tensile strength for eversion. Chytrids possess rhizoids, zygomycetes conjugation structures, basidiomycetes clamp connections. Polar tube ultrastructure diagnostically distinguishes microsporidian spores in clinical biopsy.