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Biology · 2026 · 5 marks
Sexual Reproduction in Flowering PlantsPre-fertilisation: Structures and Events5 marksApplylong answer
CBSE 2026 · Region 1 · Set 2 · Q31
(a) In angiosperms, the female gametophyte develops from a single cell of megasporangium. (i) Name that cell of megasporangium and describe the…
In angiosperms, the female gametophyte develops from a single cell of megasporangium.
(i)
Name that cell of megasporangium and describe the sequential changes it undergoes to form a mature female gametophyte.
(ii)
Draw a well labelled diagram of mature female gametophyte. Label any four parts.
Given below are certain situations related to birth control. Analyse each situation carefully and suggest appropriate contraceptive method that could be used. Also explain its mode of action. Situation $\displaystyle 1$ - To prevent entry of sperm into cervix. Situation $\displaystyle 2$ - Devices that are inserted by doctors or expert nurses in the vagina. Situation $\displaystyle 3$ - Effective emergency contraceptive. Situation $\displaystyle 4$ - Permanent method for male partner. Situation $\displaystyle 5$ - Surgical method in female to prevent pregnancy.
Marking-scheme solution
(i)
Megaspore mother cell
$\displaystyle \diamond$ Megaspore mother cell undergoes meiotic division forming four megaspores or tetrad
$\displaystyle \diamond$ Three megaspores degenerate and one remain functional .
$\displaystyle \diamond$ Functional megaspore undergoes three sequential mitotic divisions without cell wall formation to form eight nuclei
$\displaystyle \diamond$ Three nuclei arranged at micropylar end and three at chalazal end and two at the centre.
$\displaystyle \diamond$ After $\displaystyle 8$ nucleated stage cell walls are laid down to form seven celled and eight nucleate female gametophyte or embryosac.
(ii)
(Any four labelling)
Situation $\displaystyle 1$ –
Contraceptive used – Condoms by male, Diaphragms or cervical caps or vaults by female.
(any one)
Mode of Action –creates barrier for meeting of sperm and ovum .
Situation $\displaystyle 2$ – Award one mark if attempted
Situation $\displaystyle 3$ –
Contraceptive device –Pills having progestogen or progestogen – estrogen combination / IUDs within $\displaystyle 72$ hours of coitus.
Mode of Action –Pills inhibit ovulation and implantation/Alter the quality of cervical mucus to prevent entry of sperms/ Cu ions from Cu IUD increase phagocytosis of sperms/ suppress sperm motility and fertilizing capacity/ Hormone Releasing IUDs make uterus unsuitable for implantation.
Situation $\displaystyle 4$ –
Device –Vasectomy
Mode of Action –Blocks sperm Transport.
Situation $\displaystyle 5$ –
Device –Tubectomy
Mode of Action –Block gamete transport and prevent conception.
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.