So fertilization takes place within this section. Now following fertilization we have an influx of calcium ions into the cytoplasm of that form zygote. And what the influx of calcium ions does is it initiates a set of metabolic processes. 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.