after the zygote begins to divide, a fluid-filled ball of cells, called a(n) attaches to the uterine wall.

After the zygote begins to divide, a fluid-filled ball of cells, called blastocyst attaches to the uterine wall.
It is the stage of implantation during the prenatal development. The blastocyst consists of an inner cell mass and the outer layer -the trophoblast. Trophoblast surrounds the inner cell mass and a fluid-filled cavity - blastocoele. Inner cell mass will form embryo and trophoblast gives rise to the placenta.

The basic building blocks of dna and rna are nucleotides

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