Question

explain double fertilization nd trase the post fertilization events tht lead to formation of dicot seed??

Answer 1

Event of double fertilisation start when a small pollen grain from a stamen lands on the stigma of a same or different flower, after which it enters inside and reaches the ovule present inside the ovary.
Ovule consists of a embryo sac that contains seven cells. Among these one cell remains in the middle called central cell with two nuclei and remaining six cells divide into two parts and each part with three cells move to the opposite corners of the sac. The three cells closest to the micropyle (pore) differentiate into one egg cell and two synergids. These three cells together are called “three celled egg apparatus of embryo”. The other three antipodal cells degenerate.
Two pollen nuclei (male gamete) after entering inside the embryo sac fertilise the egg and the central cell. The fertilised egg produces zygote and the fertilised central cell produces endosperm. Due to these two fertilisation events fertilisation of flowering plant is also known as double fertilisation.
After fertilisation the zygote divides mitotically and transform into multicellular embryo. The endosperm also divides and grows in size to provide adequate nutrition to the embryo while developing. As the embryo and endosperm develop, the ovules also increase in size gradually to transform into seeds. The integuments dry up to give protective coating to the seeds known as seed coat. The accessory parts of the flower like petals, sepals etc. get withered and fall off and fertilised ovary develops into a fruit.