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 of the following statements?
A) Cellular determinants are equally distributed in the embryo.
B) Differentiation has occurred by the eight-cell stage.
C) Inducers have determined cell fate.
D) Polarity exists in the embryo by the eight-cell stage.
E) None of the above

Question

Quizplus · Accepted Answer

The observation that different results are achieved when an eight-cell sea urchin embryo is bisected horizontally as opposed to vertically indicates that polarity exists in the embryo by the eight-cell stage. This is because bisecting the embryo in different orientations results in different cells being exposed to different signaling factors, leading to different developmental outcomes.

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