13. Which term is used for the outer cells of the human blastocyst?
Answer: C
The term used for the outer cells of the human blastocyst is trophoblast.
The trophoblast is the layer of cells that forms the outer shell of the blastocyst, playing a crucial role in implantation and providing nourishment to the embryo.
A) Embryonic disk
The embryonic disk is a structure that forms later in development, consisting of the epiblast and hypoblast layers. It is not related to the outer cells of the blastocyst, which are specifically referred to as the trophoblast.
B) Neural plate
The neural plate is a group of cells that will eventually develop into the nervous system during embryonic development. It does not pertain to the outer cells of the blastocyst, making this option incorrect.
C) Trophoblast
The trophoblast is indeed the correct term for the outer cells of the human blastocyst. These cells are essential for the implantation of the blastocyst into the uterine wall and contribute to forming the placenta.
D) Mesenchyme
Mesenchyme refers to a type of loosely organized connective tissue that arises from mesoderm during development. It is not a term used to describe the outer cells of the blastocyst, thus rendering this option incorrect.
Conclusion
The trophoblast is the definitive term for the outer cells of the human blastocyst, as it is specifically responsible for implantation and supporting early embryonic development. Other options, such as the embryonic disk, neural plate, and mesenchyme, refer to different structures or stages in development and do not accurately describe the outer layer of the blastocyst.