CBSE 2024 · Region 4 · Set 2 · Q31 · 5 marks
(i)Explain the following phases in the menstrual cycle of a human female :(1)Menstruation(2)Follicular phase(3)Luteal phase(ii)'A proper understanding of the menstrual cycle can help immensely in family planning.' Do you agree with the statement ? Provide reasons for your answer.(i)Why does endosperm development precede embryo development in angiosperm seeds ? State the role of endosperm in mature albuminous seeds.(ii)Draw a labelled diagram showing the different embryonic stages of a dicot plant, upto a fully mature embryo.
(i)
Explain the following phases in the menstrual cycle of a human female :
(1)
Menstruation
(2)
Follicular phase
(3)
Luteal phase
(ii)
'A proper understanding of the menstrual cycle can help immensely in family planning.' Do you agree with the statement ? Provide reasons for your answer.
(i)
Why does endosperm development precede embryo development in angiosperm seeds ? State the role of endosperm in mature albuminous seeds.
(ii)
Draw a labelled diagram showing the different embryonic stages of a dicot plant, upto a fully mature embryo.
Marking-scheme solution
(i)
($\displaystyle 1$)Menstruation phase – This flow is due to breakdown of endometrium lining of uterus and blood vessels along with unfertilized ovum continues for $\displaystyle 3$-$\displaystyle 5$ days. This happens when ovum is not fertilized.
(2)
Follicular phase – In this phase follicle develops into mature
Graafian Follicle. This is known as proliferative phase because endometrium lining regenerates. It last for $\displaystyle 10$ days.
(3)
Luteal phase – This phase lasts for about $\displaystyle 10$-$\displaystyle 14$ days. This is also known as secretory phase. In this phase corpus luteum is formed which secretes large amount of progesterone that is required for maintenance of pregnancy.
(ii)
• Yes,
• Chances of fertilization are nil if abstain from Coitus from day
$\displaystyle 10$-17th day of menstrual cycle.
(i)
• The embryo development starts only after a certain amount of
endosperm is developed because it is an adaptation for assured nutrition to the developing embryo thus endosperm development precedes embryonic development
• To provide nutrition to the embryo.
(ii)
Stages in embryo development in a dicot: Zygote → Globular Embryo → Heart-Shaped Embryo (with Suspensor) → Mature embryo (Radicle, Cotyledon, Plumule).
Human ReproductionMenstrual CycleUnderstandlong_answermedium
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CBSE Class 12 Biology past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.