AP BIOLOGY

Detailed explanation-1: -Gastrulation occurs during week 3 of human development. The process of gastrulation generates the three primary germ layers (ectoderm, endoderm, mesoderm ), which primes the system for organogenesis and is one of the most critical steps of development.

Detailed explanation-2: -Gastrulation is a key phase in embryonic development when pluripotent stem cells differentiate into the three primordial germ layers: ectoderm, mesoderm and endoderm.

Detailed explanation-3: -The endoderm is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. It is the first layer to be developed.

Detailed explanation-4: -In amniotes, gastrulation occurs in the following sequence: (1) the embryo becomes asymmetric; (2) the primitive streak forms; (3) cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers.

Detailed explanation-5: -Cells in each germ layer differentiate into tissues and embryonic organs. The ectoderm gives rise to the nervous system and the epidermis, among other tissues. The mesoderm gives rise to the muscle cells and connective tissue in the body. The endoderm gives rise to the gut and many internal organs.