Question

What is the ball of cells formed after fertilization called?

Answer 1

In humans, sexual reproduction takes place in which a haploid female egg fuses with the haploid male sperm. During fertilization, the fusion of gametes occurs and the zygote is implanted in the uterus. The fusion of egg and sperm forms a zygote or fertilized human egg.

Complete answer:
After fertilization, the mitotic division occurs in zygote. The zygote divides to form a solid ball of cells which is called morula. It is a spherical structure. The 8-16 blastomeres are present in morula. After five to fourteen days of fertilization, the morula further divides and becomes a hollow bubble like structure and it is called blastocyst.
The cells of the blastocyst can be differentiated into two layers- the inner layer is called inner cell mass and outer layer is called the trophoblast. The embryo is formed from inner cell mass. All tissues of the body are formed from inner cell mass. The outer layer of the blastocyst gets attached to the wall of the uterus. This is called implantation of the embryo. The implantation is completed at the end of the second week after fertilization. The placenta is formed from the outer layer. After the completion of the third week, the three germinal layers can be differentiated in inner cell mass. These are- ectoderm, mesoderm and endoderm. The ectoderm is the outermost layer of the embryo that forms the brain, spinal cord etc. The endoderm is the innermost layer that forms internal organs such as the liver. The mesoderm is the middle layer between ectoderm and endoderm that forms the cardiovascular system, kidney etc.

Hence, the ball of cells that are formed after fertilization is called morula.

Note:
After implantation, finger-like projections start appearing from the trophoblast. The villi and cells of the uterus form placenta that acts as the connection between the mother and the developing foetus. It helps in the supply of nutrients and oxygen to the developing embryo. It also helps in the removal of carbon dioxide and other waste materials produced by developing embryo.