Question

How do the cells in a blastocyst change as it becomes an embryo?

Answer 1

cells in blastocyst can be transformed into a fetal's body and be the origin for placenta.

Explanation:

Inter cell mass is a group of cells that by dividing can create (in time) gastroderma, where there will be mesoderm, ectoderm, endoderm, that will be in charge of creating part of embryo's body.
The remaining liquid in blastocyst is connected with creating placenta in the future.