51) Implantation of the blastocyst on the uterine lining takes about
A) 1 week.
B) 2 weeks.
C) 3 weeks.
D) 4 weeks.
52) Fertilization is to zygote as
A) egg is to sperm.
B) oocyte is to ovary.
C) cleavage is to morula.
D) birth is to parturition.
53) In human embryos, the yolk sac is important because it
A) stores yolk.
B) gives rise to earliest blood cells and blood vessels.
C) stores nitrogenous wastes.
D) allows for gas exchange through the placenta.
54) The body's axis of development is determined by the
A) blastomeres.
B) epiblast.
C) notochord.
D) primitive streak.
55) Most organ systems are fully formed and ready to function in the fetus by the sixth month. Which of the following systems is the exception to this generalization because it takes longer to finish development?
A) the circulatory system
B) the respiratory system
C) the urinary system
D) the integumentary system
56) The urinary bladder is derived from which embryonic layer?
A) ectoderm
B) mesoderm
C) endoderm
D) neural crest
57) A teratogen is
A) a deformed baby.
B) a specific sedative used in the 1950s in Europe.
C) a chemical agent, infectious agent or environmental factor that causes birth defects.
D) a stage of development in the mid-fetal period.
58) The primary germ layer that ultimately produces the hair, fingernails, and toenails is
A) ectoderm.
B) mesoderm.
C) endoderm.
D) neural crest.
59) The primary germ layer that ultimately forms the serous membranes of the peritoneum is
A) ectoderm.
B) mesoderm.
C) endoderm.
D) neural crest.
60) The neural tube of the embryo develops into the
A) spinal cord.
B) neural crest.
C) sensory neurons.
D) dorsal skin.