Question

In which of the following embryonic stages does the implantation take place?

• A.

B.

C.

D.

Answer 1

Hint:-we have to resolve this as the developmental change occurs in zygote after fertilization inside the female reproductive system.it is hinted that first of all after 72 hours of fertilization implantation occurs then morulation, blastulation etc are followed.

Complete Answer:-after intercourse fertilization takes place, overall at 72 hours later means after 3 days cleavage of zygote starts.
As a result unicellular zygotes change into multicellular structures. then it follows respectively,
(I)-morula, as a result of segmentation or cleavage activity .In the later stage of cleavage, clusters of sticky, cohering, protruding blastomeres are produced, which look like mulberry. This stage is termed as a moral stage.
The mitotic division starts as the zygote moves through the isthmus of the oviduct called cleavage towards the uterus and forms 2,4,8,16 daughter cells called blastomeres .The embryo with 8 to 16 blastomeres is called a morula.
(II)-blastula, the morula continues to divide and transform into a blastocyst.
                     BLASTOCYST, blastula of eutherian and metatherian mammals is called a blastocyst because blastula is in the form of a cyst.
The blastomere in the blastocyst is arranged into an outer layer called trophoblast and an inner group of the cell attached to the trophoblast and inner cell mass. The trophoblast layer then gets attached to the endometrium and inner cell mass gets differentiated as an embryo.
In humans, the site of implantation is generally the mid-dorsal /fundus part of the uterus .Iplantation of blastocyst takes about 7-8 days after fertilization.
According to the option, A having more than 16 cells stage and also having trophoblast indicate blastula stage. But B, C and D having 4,8and 16 cell stage i.e. indicate morula Stage

So A is the correct option.

Note:- As in option figures of all stages are provided so we have to view it properly and count the cell number in every stage so that we can differentiate between all stage and got the proper stage of implations.e. after blastula stage which having trophoblast layer.