Video Transcript
The figure shows the stages of development that occur after fertilization. What is the name of structure X?
The diagram depicts the fertilization process and the early development of the zygote and the embryo. In the first image, we can see two sex cells, which are still separated. The sperm cell is smaller than the egg cell, and it has a tail for motility. Enzymes released from the sperm cell’s head interact with the layers surrounding the egg cell, allowing it to penetrate through to the cell membrane. The membranes will then fuse together, combining the cell contents. At this point, the egg cell is fertilized and the two haploid nuclei combine to form a diploid zygote with 46 chromosomes. Now that the egg cell is fertilized, it can begin to mature. The first cleavage occurs, which means that the fertilized egg divides.
At this point in the maturation process, the cell has begun making its journey down the Fallopian tube toward the uterus. Each of the two new cells, which are called blastomeres, divide again into two new cells. This is called the four-cell stage of an embryo. The cells of the embryo continue to multiply in this way. When the embryo has eight to 32 blastomeres, it is called a morula. The blastomeres of the morula continue to divide, and the morula enters the uterus. At this stage, it transforms into a blastocyst. Now, the blastocyst hatches out of the layer that originally surrounded the egg cell and attaches itself to the lining of the uterus, where it’ll start to develop into a fetus.
Now we can answer our question. The final image in the diagram labeled X is a blastocyst.
