The primitive streak of a bird embryo is the functional equivalent of the __________ in a frog.

• A. archenteron
• B. yolk plug
• C. blastocoel
• D. zona pellucida
• E. dorsal blastopore lip

Answer: (E)

Verified step by step guidance

1. Understand the concept of the primitive streak in bird embryos. It is a structure that forms during the early stages of embryonic development and is crucial for gastrulation, where cells begin to move and differentiate.
2. Learn about the dorsal blastopore lip in frog embryos. This structure is also involved in gastrulation and serves as a key organizer for the developing embryo, guiding the formation of different tissues.
3. Compare the functions of the primitive streak in birds and the dorsal blastopore lip in frogs. Both structures play a similar role in organizing the embryo and initiating the process of gastrulation.
4. Recognize that the primitive streak in birds is the functional equivalent of the dorsal blastopore lip in frogs, as both are involved in the same developmental process despite being in different species.
5. Review the other options provided (archenteron, yolk plug, blastocoel, zona pellucida) and understand why they are not equivalent to the primitive streak. The archenteron is a cavity formed during gastrulation, the yolk plug is part of the yolk sac, the blastocoel is a fluid-filled cavity in the blastula, and the zona pellucida is a protective layer around mammalian eggs.