Final answer:
The name for a fertilized egg between 3-8 weeks is an embryo, which is a crucial physiological stage for development into a fetus.
Step-by-step explanation:
The name given to the fertilized egg between 3-8 weeks is an embryo. Following fertilization, the zygote undergoes cell division and reaches the uterus as a morula, which then develops into a blastocyst. Once the blastocyst implants in the uterus, which typically occurs a week after fertilization, it enters the embryonic stage of development. This stage is characterized by rapid growth and differentiation, where the basic structures begin to form into areas that will become the head, chest, and abdomen of the human organism.
By the end of the eighth week, most organs have started forming, and the heart begins to beat. This developmental phase is crucial as it lays the groundwork for all remaining stages of life. After the eighth week and until birth, the organism is referred to as a fetus.