Practice question

Sea urchin sperm activation and chemotaxis involve dramatic intracellular ion fluxes coordinating motility. Egg jelly peptides like resact bind receptor guanylate cyclase localized on flagellar membrane, raising cGMP that opens K+ selective channels hyperpolarizing membrane, then Na+/H+ exchanger SLC9C1 raises intracellular pH activating dynein motor. Crucially Ca2+ influx through CatSper-associated channels in flagellum triggers increased asymmetric beating and acrosome reaction exocytosis. Intracellular Ca2+ oscillations also regulate turning behavior during chemotactic navigation toward egg. While K+, Na+, Mg2+ modulate excitability, Ca2+ acts as central second messenger orchestrating flagellar beat changes and secretory events.