- A Ectoderm, endoderm, and mesoderm, all sometimes thought to derive mainly from the neural crest in typical laboratory settings
- B Ectoderm (skin, nervous system), mesoderm (muscles, bones, circulatory), endoderm (gut lining, lungs, liver)
- C Trophoblast, inner cell mass, and blastocoel, formed before implantation occurs under usual circumstances
- D Mainly two layers form initially - ectoderm and endoderm, with little mesoderm contribution according to most researchers
Correct answer: B. Ectoderm (skin, nervous system), mesoderm (muscles, bones, circulatory), endoderm (gut lining, lungs, liver)
Explanation: Gastrulation: ectoderm forms skin and entire nervous system; mesoderm forms muscles, bones, blood vessels, heart, kidneys, gonads; endoderm forms gut epithelium, liver, pancreas, lungs, thyroid. The development of all organs (organogenesis) follows from these three primary layers.
Concept context
Male and female reproductive systems, gametogenesis, fertilization, implantation, pregnancy, and reproductive health.