There is no point in discussing when a fetus or embryo becomes a human.
There is no answer, anyone who asserts and answer is just stating their opinion.

This is a paradigmatic example of the “paradox of the Heap”
http://en.wikipedia.org/wiki/Paradox_of_the_heap

Everyone agrees that a fetus the day b4 birth is a human, and
Everyone agrees that a zygote (the first cell egg+sperm) isn’t a human
So when does it become a human?
Never, there is no point when it does. But it does.
It’s a paradox, philosophers have looked at this for a long time.
So have scientists. There is no biological indicator of being “human”