Embryogenesis and Germ Layer Formation (2C) Practice Test

Researchers label a population of cells in the middle germ layer of a gastrula-stage embryo and later identify labeled descendants within contractile tissue surrounding tubular structures that transport blood. The labeled descendants are organized into elongated, striated cells with abundant mitochondria. Baseline: mesoderm gives rise to muscle and much of the cardiovascular system.

Which structure is most likely derived from the labeled middle-layer cells?

A research vignette describes a chick embryo during gastrulation: cells that move inward and replace the hypoblast form a continuous epithelial sheet that later becomes the lining of the digestive tract. The investigators emphasize that this layer is internal, forms a tube, and is specialized for absorption and secretion. Which structure is most likely derived from this layer?