The blastopore is a structure that first becomes evident during
a. the eight-cell stage of the embryo.
b. coelom formation.
c. fertilization.
d. cleavage.
e. gastrulation.
I think that it is (e). But I am kinda thinking that it could be (d) too. PLEASE HELP!
e. gastrulation is correct.
To determine the correct answer, let's go through the options and the process of embryonic development.
a. The eight-cell stage of the embryo: At this stage, the embryo is still in the early cleavage stage, where the fertilized egg undergoes multiple rounds of cell division. The blastopore is not evident yet, so (a) is incorrect.
b. Coelom formation: Coelom formation refers to the development of the body cavity, which occurs later in embryonic development. The blastopore is not directly related to coelom formation, so (b) is incorrect.
c. Fertilization: Fertilization is the process in which the sperm and egg unite, resulting in the formation of a zygote. The blastopore is not formed during fertilization, so (c) is incorrect.
d. Cleavage: Cleavage is the series of rapid cell divisions that follow fertilization, resulting in the formation of a multicellular embryo. The blastopore becomes evident after the cleavage stage, during a process called gastrulation. So, (d) is incorrect.
e. Gastrulation: Gastrulation is the process through which the three primary germ layers (ectoderm, mesoderm, and endoderm) are formed, and the cells rearrange to form the three basic tissue layers of the embryo. It is during gastrulation that the blastopore becomes apparent. This makes (e) the correct answer.
Therefore, the correct answer is (e) gastrulation.