Question

The human embryo, with 8 to 16 blastomere is called:
A. Morula
B. Blastula
C. Gastrula
D. Fetus

Answer 1

Hint: Blastomeres or cells are formed during the first stage of embryonic development whenever the fertilized egg divides into two cells, four cells, eight cells, and sixteen (via cell division).

Complete Step by Step Answer:
The mammalian zygote begins the cleavage process shortly after fertilization, which refers to the process through which the zygote quickly divides without growing to become multicellular. Cleavage replicates the genome and then divides the cells in half, however, unlike ordinary mitosis, there isn't a growth phase between divisions during cleavage.
The first division takes place about a day after fertilization, and successive divisions take place every 12 to 24 hours. The zygote divides multiple times to form a morula, an embryonic stage composed of a solid, compact mass of 16 or more cells. The morula is the first embryonic stage in which mammalian cells can be classified as internal or external. Whenever the mammalian morula attains the 64-cell stage, the external and internal cells detach into separate lineages. Morula is the embryo that consists of 8-16 blastomeres.
The morula stage is then differentiated into the blastula stage, which occurs after the egg has divided into 200-300 cells. The rapid division of cells that occurs in the zygote is referred to as cleavage. The blastula contains a fluid-filled cavity known as the blastocoel. The blastula can then undergo either meroblastic or holoblastic cleavage based on the quantity of yolk required by the embryo. The blastula reconfigures itself and forms folds that result in the embryo's three germ layers. The gastrula stage is the name given to this stage. Such germ layers then inevitably lead to the developing embryo's organs and body system.
Therefore the correct option is A.

Note: A fetus is an unborn child derived from an embryo. The fetal stage begins nine weeks after fertilization in humans. Morula develops into the blastula in a process called blastulation whereas gastrulation is the process by which the blastula develops into the gastrula.