Fertilization and implantation
Read the following passage carefully and answer the given questions.
During copulation semen is released by the penis into the vagina. The motile sperms swim rapidly, pass through the cervix, enter into the uterus and finally reach the ampullary region of the fallopian tube. The ovum released by the ovary is also transported to the ampullary region where fertilisation takes place. During fertilization, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. This induces the completion of the meiotic division of the secondary oocyte. The second meiotic division is also unequal and results in the formation of a second polar body and a haploid ovum (ootid). Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote. The zygote undergoes cleavage and forms a blastocyst, which gets implanted in the endometrium of the uterus after about 6-7 days of fertilization. Successful fertilization leads to pregnancy.
Implantation takes place in -
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Endometrium
The blastocyst has an outer layer, the trophoblast, and an inner cell mass. The trophoblast sticks to the endometrium, the inner glandular lining of the uterus. The uterine cells then divide fast and cover the blastocyst, so it becomes embedded in the endometrium. This is implantation, and it leads to pregnancy.
(1) Ovary — Incorrect. The ovary makes and releases the ovum. The embryo does not reach it.
(2) Endometrium — Correct. The blastocyst embeds in it.
(3) Cervix — Incorrect. This is the narrow lower part of the uterus. With the vagina, it forms the birth canal.
(4) Vagina — Incorrect. It receives the semen at copulation and is part of the birth canal.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Fertilisation and Implantation – “… The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus (Figure 2.11 step H). This is called implantation and it leads to pregnancy.”
