How is sperm able to fertilize an egg

The sperm plasma combines with the egg plasma then the flagellum separates from the head of the sperm then the two combined move up into the fallopian tube to plant itself into the uterus to make a baby

A women's body sheds the thick lining of the uterus, and her period starts. If one sperm does make its way into the fallopian tube and burrows into the egg, it fertilizes the egg. The egg changes so that no other sperm can get in. At the instant of fertilization, the baby's genes and sex are set.