A(an) ________ begins as a one-cell structure that is created when a sperm and egg merge.

A) embryo
B) placenta
C) fetus
D) zygote

Zygote

The initial cell formed when a sperm cell fertilizes an egg cell, marking the beginning of a human's genetic development.

Embryo

An early stage of development in multicellular organisms, in humans, it refers to the first eight weeks of development post-conception.

Placenta

A temporary organ that develops in female mammals during pregnancy, connecting the fetus to the uterine wall for nutrient uptake, waste elimination, and gas exchange via the mother's blood supply.