A totipotent embryonic cell has the most cell potency. Which of the following is most likely to be totipotent?
(A) 8-cell zygote
(B) Inner cell mass
(C) Mesoderm
(D) Digestive tract

Embryogenesis is a carefully timed and well-organized process. As a single-celled zygote divides and grows into hundreds and thousands of cells, a process called differentiation occurs wherein certain areas of the embryo become specialized to become different types of tissue. As differentiation continues, the level of specificity increases, and the cell potency decreases until highly specialized unique tissues and organs develop. The figure below shows 12 stages of development of human embryos.

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1 fertilized 6 polar 2 body 10 blastomere O ectoderm egg zona hatching 3 8-cell zygote cell adhesion 7 8 invades uterine wall 11 mesoderm endoderm mesoderm forms o 4 mesoderm spreads 16-cell morula cell mass differentiates -epiblast trophoblast- 5 inner cell mass 12 hypoblast trophoblast 9 blastocyst bilaminar disc forms amniotic sac grows