For example, it initiates the Cortical reaction and this leads to the formation of a membrane that basically is impermeable to sperm cells. So no other sperm cell can actually make its way into that xcel. Now the influx of calcium ions also initiates other metabolic processes such as protein synthesis. And eventually this leads to the process of mitosis. So the zygote begins to divide following, shortly afterwards, the process of fertilization. Now why would the zygote actually want to or need to divide?