CBSE 2025 · Region 2 · Set 1 · Q31 · 5 marks
Student to attempt either option (A) or (B).(A)Describe the process of megasporogenesis in an angiosperm.(ii)Draw a diagram of a mature embryo sac of an angiosperm. Label its any four parts.The reproductive cycle in the female primates is called menstrual cycle. The first menstruation begins at puberty. Answer the following questions :(i)Name the four phases of menstrual cycle in a proper sequence.(ii)How long does the menstrual phase last in a menstrual cycle ?(iii)When and why hormones estrogen and progesterone reach their peak levels respectively, in the menstrual cycle?(iv)Give the significance of LH surge.
Student to attempt either option (A) or (B).
(A)
Describe the process of megasporogenesis in an angiosperm.
(ii)
Draw a diagram of a mature embryo sac of an angiosperm. Label its any four parts.
The reproductive cycle in the female primates is called menstrual cycle. The first menstruation begins at puberty. Answer the following questions :
(i)
Name the four phases of menstrual cycle in a proper sequence.
(ii)
How long does the menstrual phase last in a menstrual cycle ?
(iii)
When and why hormones estrogen and progesterone reach their peak levels respectively, in the menstrual cycle?
(iv)
Give the significance of LH surge.
Marking-scheme solution
(i)
( Meiosis)
Megaspore mother cell
Tetrad
(2n) (n)
$\displaystyle 3$ Mitosis without cell wall formation / Degeneration of $\displaystyle 3$ cells
Free Nuclear division (one functional megaspore left)
(n)
(Cell wall formation)
$\displaystyle 8$ nuclear stage Embryo sac ($\displaystyle 7$ celled $\displaystyle 8$ nucleated stage)
(ii)
(i)
Menstrual phase → proliferative / follicular phase → ovulatory
phase → luteal / secretory phase.
(ii)
$\displaystyle 3$ – $\displaystyle 5$ days.
(iii)
Estrogen reaches its peak during proliferative phase just before ovulation, because it is secreted by the growing follicles.
Progesterone reaches its peak during luteal phase or secretory phase, it is because progesterone is secreted by corpus luteum.
(iv)
LH surge induces rupture of Graafian follicle / the release of ovum /ovulation.
Human ReproductionMenstrual CycleApplylong_answermedium
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CBSE Class 12 Biology past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.