CBSE 2025 · Region 4 · Set 1 · Q31 · 5 marks
(i)Explain how does double fertilisation take place in a flowering plant.(ii)Write the fate of the products of double fertilization in these plants.(i)Explain the structure of testicular lobules in human male reproductive system. Name the two types of cells present in the seminiferous tubules and state their role.(ii)Describe the role of hypothalamic hormone GnRH in spermatogenesis.
(i)
Explain how does double fertilisation take place in a flowering plant.
(ii)
Write the fate of the products of double fertilization in these plants.
(i)
Explain the structure of testicular lobules in human male reproductive system. Name the two types of cells present in the seminiferous tubules and state their role.
(ii)
Describe the role of hypothalamic hormone GnRH in spermatogenesis.
Marking-scheme solution
(i)
After entering one of the synergids the pollen tube releases the two male gametes into the cytoplasm of the synergid, one of the male gametes moves towards the egg cell and fuses with its nucleus thus completing the syngamy to form zygote, the other male gamete moves towards the two polar nuclei located in the central cell and fuses with it causing triple fusion to form Primary endosperm nucleus (PEN) or
Primary endosperm cell (PEC).
(ii)
Primary endosperm cell (PEC) and develops into the endosperm, while the zygote develops into an embryo.
(i)
• Each testicular lobule consists of $\displaystyle 1$-$\displaystyle 3$ highly coiled seminiferous
tubules, in which sperms are produced.
• Two types of cells
− Male germ cells/ spermatogonia, undergo meiotic divisions finally leading to sperm formation
− Sertoli cells, provide nutrition to the germ cells.
(ii)
− GnRH acts at the anterior pituitary gland, and stimulates secretion of (two) gonadotropins,
− luteinising hormone (LH)
− follicle stimulating hormone (FSH).
Sexual Reproduction in Flowering PlantsDouble FertilisationUnderstandlong_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.