-4. In the diagram below, the stages of development in a frog embryo are NOT arranged in the correctorder. In what order should they be placed to show the normal sequence of development in theembryo? What process is occurring in this diagram?B.DDorsal lip ofblastoporeDorsal lip ofblastoporeDorsal lip ofblastoporeDorsal lipblastopon

Gastrulation is the process where the blastomere cells undergo dramatic movements that leads to change in their position with respect to one another. This cell rearrangement is called gastrulation and at the end of the gastrulation, the embryo contains three germ layers i.e., endoderm, mesoderm, and ectoderm. The above diagram shows the different stages in the gastrulation of the frog embryo. The gastrulation begins at the future dorsal side around the marginal zone. At the end of the gastrulation, three germs layers are visible, with the endoderm inside and surrounded by mesoderm and ectoderm. The correct sequence of order for the given stages of frog gastrulation is as follow : D, C, A, B. Gastrulation in frog initiates on the future dorsal side of the embryo. The future dorsal side is below the equator in the grey crescent region. The cell invaginate and form a slit-like blastopore, thereby leading to the formation of the dorsal lip of the future blastopore. The gastrulation in frogs begins in the marginal zone, the region where animal and vegetal hemispheres meet, it is present in the equator region of the embryo. We can see the initiation of gastrulation in the diagram labeled as D. During the next stage, we can see the start of the archenteron development, where cells of the animal poles spread out leading to the formation of endoderm and mesoderm. This stage is marked as C. The next stage marked the shift in the blastopore and more prominent archenteron development, animal cells undergo epiboly and converge at the blastopore. During this stage, we can see two cavities, one is blastocoel and another archenteron. Endoderm and mesoderm can be clearly seen in the diagram. This stage is marked as A. This is the final stage, archenteron has expanded and destroyed blastocoel. So, we will again see only one cavity i.e., archenteron. Three germ layers are also distinguished at this stage. We can also see the ventral lip of the blastopore and while forming the ventral lip, the endodermal cells are visible in the vegetal surface, this patch of endoderm is called yolk plug. This stage is marked as B. So, the correct sequence in the above diagram is D, C, A, B.