Final answer:
After 8 weeks, an embryo is referred to as a fetus, marking the transition from the embryonic stage of development to the fetal stage, which continues until birth.
Step-by-step explanation:
After 8 weeks, an embryo is called a fetus. The embryonic stage includes profound changes where the organism grows in size, its organs start to form and begin to function, and it undergoes cell division, migration, and differentiation. By the end of the 8th week after fertilization, the embryo transforms into a fetus, which lasts from the beginning of the 9th week up until birth at around 38 weeks after fertilization.
The distinction is significant because the terms embryo and fetus denote specific periods in the prenatal development of a human being. An embryo is referred to as such from the time of implantation until the end of the 8th week. The term fetus is used from the start of the 9th week when the developing organism takes on a more recognizable human shape as the 'tail' begins to disappear and continues to develop its organ systems further.