The archenteron develops intoa. the mesoderm.b. the endoderm.c. the placenta.d. the lumen of the digestive tract.

During the development of most animals, cleavage leads to __________.

Which of the following correctly lists the embryonic stages in the order that they develop?

The cortical reaction of sea urchin eggs functions directly ina. the formation of a fertilization envelope.b. the production of a fast block to polyspermy.c. the generation of an electrical impulse by the egg.d. the fusion of egg and sperm nuclei.

Which of the following is common to the development of both birds and mammals?a. holoblastic cleavageb. epiblast and hypoblastc. trophoblastd. gray crescent

What structural adaptation in chickens allows them to lay their eggs in arid environments rather than in water?a. extraembryonic membranesb. yolkc. cleavaged. gastrulation

If an egg cell were treated with EDTA, a chemical that binds calcium and magnesium ions,a. the acrosomal reaction would be blocked.b. the fusion of sperm and egg nuclei would be blocked.c. the fast block to polyspermy would not occur.d. the fertilization envelope would not form.

In humans, identical twins are possible becausea. extraembryonic cells interact with the zygote nucleus.b. convergent extension occurs.c. early blastomeres can form a complete embryo if isolated.d. the gray crescent divides the dorsal-ventral axis into new cells.

Cells transplanted from the neural tube of a frog embryo to the ventral part of another embryo develop into nervous system tissues. This result indicates that the transplanted cells werea. totipotent.b. determined.c. differentiated.d. mesenchymal.