Question

1. using your lecture notes and the textbook, answer the following questions: a) what is a zygote? what events lead to its formation? b) which structure undergoes mitosis to become the chorion? amnion? yolk sac? c) name two differences between a morula and blastocyst. d) at what point is a developing human called an embryo? e) what structures do the epiblast/hypoblast become in later stages? 3. use textbook figure 28.7 (d) to identify the following structures on the 25 - day and 4 - week embryo models:

Explanation:

a) A zygote is a fertilized egg cell formed when a sperm cell fuses with an egg cell during fertilization.
b) Trophoblast cells undergo mitosis to form the chorion. The amnion and yolk - sac have different developmental origins.
c) A morula is a solid ball of cells, while a blastocyst has a fluid - filled cavity (blastocoel) and distinct cell layers (inner cell mass and trophoblast).
d) A developing human is called an embryo from the time of fertilization until the end of the 8th week of development.
e) The epiblast gives rise to the three germ layers (ectoderm, mesoderm, endoderm) and contributes to the embryo proper. The hypoblast forms part of the yolk - sac.

Answer:

a) A zygote is a fertilized egg formed by sperm - egg fusion.
b) Trophoblast for chorion.
c) Morula is solid; blastocyst has a cavity and distinct layers.
d) From fertilization until 8th week.
e) Epiblast forms germ layers and embryo proper; hypoblast forms part of yolk - sac.