Different results are achieved when an eight-cell sea urchin embryo is bisected horizontally as opposed to when it is bisected vertically.This observation supports which statement?
A) Cellular determinants are equally distributed in the embryo.
B) Differentiation has occurred by the eight-cell stage.
C) Inducers have determined cell fate by the eight-cell stage.
D) Polarity exists in the embryo by the eight-cell stage.
E) All cells of the eight-cell stage are totipotent.

Question

Quizplus · Accepted Answer

The observation that different results are achieved when an eight-cell sea urchin embryo is bisected horizontally as opposed to when it is bisected vertically suggests that there is polarity in the embryo by the eight-cell stage. This means that the cells of the embryo are already differentiating and have distinct orientations or directions, indicating that cell fate is partially determined.

Different Results Are Achieved When an Eight-Cell Sea Urchin Embryo