Final answer:
The posterior marginal zone in chick embryos is crucial for establishing the antero-posterior axis which differentiates the body into anterior (motor functions) and posterior (sensory functions) regions, contributing to the overall body plan.
Step-by-step explanation:
The student's question concerns the developmental biology of chick embryos, particularly the role of the posterior marginal zone in specifying the posterior end of the antero-posterior axis. This axis is one of the three main axes formed during the development of vertebrates, including the lateral-medial (left-right), dorsal-ventral (back-belly), and antero-posterior (head-feet) axes. In one of the key experiments in developmental biology by Spemann and Mangold, they demonstrated that the position of cells in the embryo can influence the development of the organism's body plan. Further research identified many genes responsible for the axis formation. In the context of the chick embryo, the posterior marginal zone plays a critical role in establishing the antero-posterior axis, which affects the positioning of the neural tube and the differentiation of the nervous system into anterior regions associated with motor functions and posterior regions responsible for sensory functions.