The specific mechanisms that underlie variousphysiological processes are often quite similar. Explain in detail how the movement of sodium (Na+) down its concentrationgradient is involved in four very different biological processes: sea urchin fertilization, kidneyfunction, action potentials in neurons, and muscle contraction. Then select ONE of these processes, and explain how the movement of calcium ions (Ca+) down their concentration gradient is involved in acontinuation of that physiological process.