Question

at the beginning of the third week after conception, the developing fertilized egg is called a(n):
fetus.
zygote.
embryo.
teratogen.

Explanation:

• A zygote is the initial cell formed when a sperm and egg fuse (right after conception).
• A fetus is the developing baby from about 9 weeks after conception until birth.
• A teratogen is an agent that can cause birth defects (not a stage of development).
• The embryonic stage lasts from about 2 - 8 weeks after conception. At the beginning of the third week after conception, it is still in the embryonic stage.

Answer:

embryo.