(a) (i) Explain how does double fertilisation take place in a flowering plant. (ii) Write the fate of the products of double fertilization in these…

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).

Primary endosperm cell (PEC) and develops into the endosperm, while the zygote develops into an embryo.

• 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.

− GnRH acts at the anterior pituitary gland, and stimulates secretion of (two) gonadotropins,

− luteinising hormone (LH)

− follicle stimulating hormone (FSH).