Final answer:
Embryology studies the embryonic development of an organism, where the correct term for a developing organism shortly after implantation is 'embryo'. This stage lasts until the eighth week post-fertilization, followed by the fetal stage.
Step-by-step explanation:
Embryology is the study of the development of an embryo, which is a stage in the development of a new organism. The correct answer to the question is option 2) embryo. The zygote, which is a fertilized egg produced by the union of a sperm and an egg, undergoes a series of mitotic divisions and developmental stages including the morula and blastocyst stages. After the blastocyst implants itself in the uterine wall, it is referred to as an embryo. This embryonic stage lasts until the end of the eighth week after fertilization, after which the developing organism is known as a fetus. Throughout pregnancy, the amniotic sac, placenta, and umbilical cord develop to support and nourish the growing embryo.