Final answer:
During the embryonic stage, which begins two weeks after conception, a developing baby's organs and limbs begin to form. This critical phase of development is when all major organs are essentially formed.
Step-by-step explanation:
A developing baby's organs and limbs begin to form during the embryonic stage of prenatal development, which begins after conception. The embryonic stage starts after the zygote implants itself into the uterus lining, which is typically around two weeks after conception, and lasts for about six weeks.
During this period, the body and internal organ structures of the embryo start to develop, while the neural tube, which will later become the brain and spinal cord, begins to form. By the end of the embryonic stage, all the major organs and limb buds have been essentially formed.
It is important to understand that the continued growth and development of these structures occur during the fetal stage, which begins at 9 weeks post-fertilization and lasts until birth.