Read each question carefully. If the statement is false, provide the correct statement. False Sodium influx from the seawater leads to a change in membrane potential that causes the fast block of polyspermy. The cortical reaction leads to a modification of the vitelline membrane or the zona pellucida that prevents additional sperm from fertilizing the egg. False The blastocoel in replaced by the archenteron during frog gastrulation .
Bilateral animals have three axes of symmetry.
Which axis is established first in frog embryos after fertilization. Illustrate the meaning of the term competence by using the example of lens induction as an experimental system. Thus, the head ectoderm is competent to form lens. In contrast, ectopic transplantation of the optic vesicle into the trunk does not lead to the ectopic formation of a lens from trunk ectoderm. Hence, the trunk ectoderm is not competent to form lens.