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Biology · 2023 · 5 marks
CBSE 2023 · Region 1 · Set 2 · Q31
(a) (i) When and how does foetal ejection reflex begin? (ii) Pituitary gland and uterine muscles play an important role during parturition. Explain.…
(i)
When and how does foetal ejection reflex begin ?
(ii)
Pituitary gland and uterine muscles play an important role during parturition. Explain.
(iii)
A functional mammary gland is a characteristic of all female mammals. Given below is a diagrammatic sectional view of a mammary gland. Identify the parts $\displaystyle 1$, $\displaystyle 2$ and $\displaystyle 3$, and mention one function of each of them.
(i)
How are the characteristic features of pollen, anther and stigma of a maize plant suited for pollination by wind?
(ii)
How do you justify that:
(1)
Pollen grains are recovered from fossils?
(2)
Micropyle remains as a small pore in the seed coat of a fully developed seed?
Marking-scheme solution
(a) (i) • When foetus is fully mature/ after completion of gestation periods / after
completion of pregnancy
mild uterine contractions originate in response to the signal from a fully developed foetus and placenta
(ii) Foetal ejection reflex triggers a release of oxytocin from the maternal pituitary,
oxytocin acts on uterine muscles and causes contractions and expulsion of baby out of the uterus.(iii) $\displaystyle 1$- Mammary lobes, has clusters of cells called alveoli.
2 - Mammary alveolus, secrete milk.
$\displaystyle 3$-Lactiferous duct, through this milk is sucked out.
OR
(b) (i) • Pollen- light / non-sticky, to travel easily through air
// produce in enormous amount, to compensate the wastage during pollination
• Anther – well exposed, pollen easily dispersed into wind current
• Stigma – Large / often feathery, to easily trap air-borne pollen grains
(ii) ($\displaystyle 1$) Pollen grains have hard outer layer exine made up of sporopollenin, which is one of the most resistant organic material known / no enzyme can degrade sporopollenin.
($\displaystyle 2$) It allows the entry of water, oxygen into the seed at the time of germination.
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CBSE Class 12 Biology past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.