Final answer:
The opening where gastrulation occurs is called the blastopore, which eventually becomes either the anus or the mouth, depending on whether the organism is a deuterostome or a protostome. This is a key event in the formation of the digestive system and the primary body plan of an organism.
Step-by-step explanation:
The opening where gastrulation occurs is called the blastopore. During the process of gastrulation, the blastopore is the initial indent that forms on the surface of the embryo. It deepens and becomes the anus in the case of deuterostomes, or the mouth in protostomes, thereby determining the organism's digestive system orientation. This process is significant as it leads to the formation of the embryonic germ layers and the subsequent development of the body plan and organ systems in an organism. After the blastopore forms, gastrulation proceeds with the further folding and rearrangement of cells within the blastula. This development forms three germ layers known as the ectoderm, mesoderm, and endoderm, collectively responsible for differentiating into various tissues, organs, and organ systems during organogenesis. The formation of these germ layers marks the transition from a simple blastula to a more complex gastrula, setting the stage for the next phases of embryonic development, including neurulation and the establishment of the body's overall structure.