Question

Which one of the following is initiated by the secretion of trophoblast.
(a) Blastulation
(b) Gastrulation
(c) Implantation
(d) Cleavage

Answer 1

Hint: Important process in the development of the embryo that begins on the 6th day after fertilization which is aided by the proteolytic enzymes produced by trophoblast cells.

Complete answer:
After the completion of cleavage or blastulation, the embryo has a central cavity called the blastocoel. Now the embryo has a superficial flat cell layer and an inner cell mass. The cells on the exterior of this early embryo develop into trophectoderm also called trophoblast which is the outer epithelium of blastocyst. A blastocyst is formed while the early embryo passes through the fallopian tubule. The blastocyst hatches out of the envelope by lysing its wall with the help of the enzyme called strypsin. The cells of the trophoblast stick to the walls of the uterine endometrium. This is called Implantation, initiated by trophoblast

Additional Information: - When the number of daughter cells is 16 to 32, the solid ball of cells is called a morula. This undergoes cleavage or blastulation and forms blastocoel in the embryo. This develops into trophoblast which initiates the process of implantation
- This trophoblast attaches to the wall of the uterine endometrium and forms a part of the fetal part of the placenta later. The trophoblast invades the endometrium of the uterus.

So, the correct answer is 'implantation'

Note: In humans, the process of implantation begins on the 6th day after fertilization which is aided by the proteolytic enzymes that are produced by the cells of the trophoblast.
After implantation, an important dynamic process in the development of an early embryo called gastrulation which involves the movement of cell mass to their definite positions in the embryo and forms three germ layers.