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Multiple Choice
During the embryonic stage, the primary germ layers develop from the:
A
yolk sac
B
inner cell mass of the blastocyst
C
trophoblast
D
chorion
Verified step by step guidance
1
Understand the context: The question is about the embryonic stage of development, specifically the origin of the primary germ layers (ectoderm, mesoderm, and endoderm). These layers are crucial as they give rise to all tissues and organs in the body.
Identify the key structures: The options provided include the yolk sac, inner cell mass of the blastocyst, trophoblast, and chorion. Each of these structures plays a role in embryonic development, but only one is directly responsible for forming the primary germ layers.
Clarify the role of the inner cell mass: The inner cell mass (ICM) of the blastocyst is a group of cells that will develop into the embryo itself. It is from this structure that the primary germ layers are derived during gastrulation.
Eliminate incorrect options: The yolk sac primarily provides nutrients during early development, the trophoblast contributes to the formation of the placenta, and the chorion is an extraembryonic membrane that also supports placental development. None of these directly form the primary germ layers.
Conclude: The primary germ layers (ectoderm, mesoderm, and endoderm) develop from the inner cell mass of the blastocyst during the embryonic stage.