Q.Name the two parts into which a blastocyst differentiates.

Morula, blastula and gastrula are three successive stages of early embryonic development, each marking a key structural transformation.

After fertilisation, the zygote develops through a defined sequence of stages as it travels down the fallopian tube and implants in the uterus:

1. Morula: formed by repeated mitotic (cleavage) divisions of the zygote. It is a solid, compact ball of cells (blastomeres), resembling a mulberry (hence the name, from Latin "morus" = mulberry), typically reaching this stage around the 16-cell mark.

2. Blastula (Blastocyst in humans): as the morula continues dividing and moves further down the tube, a fluid-filled cavity (blastocoel/blastocystic cavity) forms inside it, converting the solid ball into a hollow sphere. In humans this stage is called the blastocyst, differentiated into an outer layer, the trophoblast (which later forms the placenta), and an inner cell mass (which develops into the embryo proper).

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