All GRE Subject Test: Biology Resources
Example Question #1 : Understanding Organogenesis
Which germ layer gives rise to the digestive tract?
The three primary germ layers are the ectoderm, mesoderm, and endoderm. There are some general structures that can be attributed to the germ layers during development. The ectoderm gives rise to the outer coverings of the body, such as the skin, and to the central nervous system. The ectoderm produces the notochord and primitive neural structures very early in development. The mesoderm gives rise to the muscles and bones. Finally, the endoderm gives rise to the digestive tract and the liver.
Example Question #41 : Biology
Formation of the primitive streak occurs during what stage of embryogenesis?
The primitive streak forms in the blastula stage and establishes symmetry (left-right and cranial-caudal body axes). This spatial differentiation determines the site of gastrulation and initiates formation of the three germ layers. The epiblast (precursor to the ectoderm) invaginates to form the primitive streak. Cells from the primitive streak give rise to the mesoderm and the endoderm. Formation of the primitive streak marks the beginning of gastrulation.
Example Question #2 : Understanding Organogenesis
The inner cell mass (or embryoblast) of the blastocyst gives rise to all of the following layers except __________.
the primitive endoderm
The blastula, or blastocyst, is made up of blastomere cells and a fluid-filled cavity called the blastocoel.
There are two regions of the blastocyst: the inner cell mass and the trophoblast. The inner cell mass gives rise to the primitive endoderm and the epiblast, which later gives rise to the three germ layers during gastrulation. The trophoblast is the layer of cells forming the outer ring of the blastocyst. It secretes factors to make the blastocoel and is kept separate from the inner cell mass. All fetal structures eventually develop from the inner cell mass, while the trophoblast helps maintain the fetal environment and placenta.