CBSE 2026 · Region 1 · Set 1 · Q31 · 5 marks
Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site where fertilization takes place.(b)Case studies of some couples are given below. They were not able to have kids even though the parents were not taking any precautions. They also do not wish to adopt a child or take the help of donors. Study these cases and suggest an appropriate Assisted Reproductive Technology that could help them. Case I – Female – Normal ReportsMale – Normal sperms but no connection between epididymis and vas deferens.Case II – Female – Normal eggs but Fallopian tube blocked.Male – Normal sperms. Male reports are normal.Case III – Female – Normal Reports.Male – Low sperm count with less motility.(ii)Copper releasing intrauterine devices are very effective and popular contraceptive devices. Name any two copper releasing IUDs. Write two reasons that make them effective contraceptives.
Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site where fertilization takes place.
(b)
Case studies of some couples are given below. They were not able to have kids even though the parents were not taking any precautions. They also do not wish to adopt a child or take the help of donors. Study these cases and suggest an appropriate Assisted Reproductive Technology that could help them.
Case I – Female – Normal Reports
Male – Normal sperms but no connection between epididymis and vas deferens.
Case II – Female – Normal eggs but Fallopian tube blocked.
Male – Normal sperms. Male reports are normal.
Case III – Female – Normal Reports.
Male – Low sperm count with less motility.
(ii)
Copper releasing intrauterine devices are very effective and popular contraceptive devices. Name any two copper releasing IUDs. Write two reasons that make them effective contraceptives.
Marking-scheme solution
After the entry of sperm into female gamete, it undergoes meiotic division II, to produce haploid ovum ie ootid, then the nucleus of sperm and ootid fuse together to form zygote, zygote moves through the isthmus of oviduct towards uterus and it undergoes mitotic division or cleavage to form blastomeres, the embryo with $\displaystyle 8$ to $\displaystyle 16$ blastomere is called morula and it further divides and transforms into
Blastocyst, blastocyst have outer layer trophoblast and inner cell mass and the trophoblast layer of blastocyst gets attached to endometrium,
Uterine wall divide rapidly and covers blastocyst and this it gets embedded in the endometrium of uterus this is called implantation.
• The site of fertilization is-
ampullary region of fallopian tube /isthmus ampullary junction of fallopian tube.
(b)
Case I
In vitro fertilization followed by zygote intra fallopian transfer or ZIFT /
In vitro fertilization followed by Intra uterine transfer or IUT /
Intra Uterine insemination or IUI / Artificial insemination or AI .
Case II -
Invitro fertilization followed by IUT
Case III -
Intra Cytoplasmic Sperm Injection or ICSI / Artificial insemination or
AI / Intra Uterine insemination or IUI.
(ii)
The copper releasing IUD’s are CUT, Cu7, Multiload $\displaystyle 375$ (Any two)
Copper releasing IUD’s increases phagocytosis of sperms within the uterus,
Cu ions released suppress sperm motility and the fertilising capacity of sperms.
Human ReproductionFertilisation and ImplantationApplylong_answermedium
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CBSE Class 12 Biology past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.