Final answer:
During the prenatal stage, the fertilized egg is called a zygote. It undergoes rapid cell division and transforms into a blastocyst before implanting in the uterus and becoming an embryo. The embryonic stage lasts until the end of the 8th week after fertilization.
Step-by-step explanation:
The fertilized egg is called a zygote. It is the result of the fusion of a sperm and egg during conception. The zygote then undergoes rapid cell division and travels down the fallopian tube towards the uterus. After several days, it reaches the uterus and forms a hollow ball of cells called a blastocyst. As the blastocyst implants in the uterus, its internal cell mass, known as the embryoblast, transforms into an embryo. The embryonic stage lasts until the end of the 8th week after fertilization, after which the embryo is called a fetus.