Practice question

Slow block provides long-lasting barrier after momentary electrical block decays. Fertilization triggers phospholipase C activation generating IP3 that opens endoplasmic reticulum calcium channels, creating traveling calcium wave across egg cortex. Elevated calcium drives SNARE-dependent exocytosis of cortical granules releasing proteases that sever bindin receptor EBR1 connections, glycosaminoglycans that osmotically lift envelope, and ovoperoxidase producing dityrosine crosslinks hardening envelope. Resulting fertilization envelope is physically elevated and biochemically unreceptive, preventing late sperm entry. Membrane potential change mediates fast block, seawater calcium influx insufficient, and acrosomal vesicle fusion belongs to sperm not egg.