Practice question

Zona pellucida is mammalian extracellular coat synthesized by oocyte and granulosa cells composed of sulfated glycoproteins forming porous matrix. It is evolutionarily and functionally homologous to vitelline envelope surrounding sea urchin and other invertebrate eggs. Both mediate species-restricted sperm binding, stimulate acrosome reaction, and after fertilization undergo cortical granule-induced modifications causing envelope elevation or hardening establishing block to polyspermy. Vitelline envelope can be distinguished from jelly layer external to it, much as zona distinct from cumulus. Analogy underscores conserved fertilization strategy across phyla, reproductive biology and developmental patterning principles.