Membrane
No, it is not a preposition. The word surrounds is a verb form.
she has an embryo.
There are no perfect rhymes for the word embryo.
the word embryo has 3 syllables. em-bry-o
embryophyte embryo=seed phyte=group
embryo
One would think it's embryo but a zygote is not a embryo yet, it is the early stage of what will become a embryo. Zygote is the word used and you can use the word cell since a zygote is the initial cell formed after a sperm and egg have joined. After 1 week it has transformed into a embryo.
Embryo is a noun and can be used as such in an almost infinite number of sentences. One such sentence might be "An embryo is a developing, growing, multicellular organism."
pregnant
the epidermis, it surrounds the toenail and fingernail
Wall
Zygote is pre-embryonic and a fetus is post-embryonic however I don't know a perfect synonym for embryo.