In the embryo versus zygote distinction, which option correctly describes the embryo?

• A. An unfertilized egg
• B. The fertilized egg prior to implantation
• C. The developing organism from about two weeks after fertilization through the second month
• D. The final stage of fetal development

Answer: (C)

The point being tested is how developmental stages are named in relation to fertilization and implantation. The zygote is the fertilized egg and covers the early, pre-implantation period. The embryo, by standard usage, is the developing organism from about two weeks after fertilization up to the end of the eighth week (the second month). This window includes critical events like formation of the basic body plan and early organ development, but it is still before the period where growth and maturation are the main focus, which is labeled the fetal stage.

So the description of the developing organism from roughly two weeks after fertilization through the second month fits the embryonic stage precisely. It excludes the unfertilized egg (not fertilized) and the fertilized egg prior to implantation (the zygote), and it also excludes the later fetal period, which begins after the embryonic stage.