Layer of cells in the blastocyst with potential to give rise to specific tissues

• A. Germ layer
• B. Endoderm
• C. Inner cell mass
• D. Trophoblast

Answer: (A)

Germ layer is the concept being assessed. In early development, the embryo organizes into distinct layers that will each form specific tissues and organs. These primary layers, called germ layers, arise during gastrulation and lead to the major tissue types: ectoderm forms skin and nervous tissue, mesoderm forms muscle, bone, and the circulatory system, and endoderm lines the gut and associated organs. The term describes groups of cells destined to become particular tissues, which is why it’s the best answer for a question about a layer in the early embryo that has the potential to give rise to specific tissues. The inner cell mass inside the blastocyst is a cluster that will become the embryo itself, not a germ layer per se, and the trophoblast contributes to extra-embryonic structures like the placenta. Endoderm is one example of a germ layer, but the general idea the question targets is the germ layer as the category that differentiates into tissues.