If an eight-cell sea urchin embryo is bisected horizontally,relative to its animal-vegetal axis,
A) both halves will develop into normal,but small,sea urchins.
B) the top half will not develop,while the bottom half will produce a small sea urchin.
C) the top half will not develop,while the bottom half will produce an abnormal half sea urchin.
D) the bottom half will not develop,while the top half will produce an abnormal sea urchin.
E) the bottom half will not develop,while the top half will produce a small,but normal,sea urchin.

Question

Quizplus · Accepted Answer

Sea urchin embryos have a pattern of embryonic development called radial cleavage, which means that cell divisions are symmetrical and occur at right angles to the animal-vegetal axis. If the embryo is bisected horizontally, the top half contains only animal cells, while the bottom half contains animal and vegetal cells. Since the vegetal cells have more cytoplasm and yolk than the animal cells, they will develop into a normal, but small sea urchin. The top half, lacking vegetal cells and yolk, will not develop. Therefore, only the bottom half will produce a small sea urchin.

If an Eight-Cell Sea Urchin Embryo Is Bisected Horizontally,relative to Its