Pollen grain represents one of the following

Explanation

Process of double fertilization :
1) At the time of fertilization there will bw a total of 7 cells arranged in three groups in a mature embryo sac.
2) They are one egg (female gamet) two synergids, one central cell (secondary or polar nucleus) and three antipodals.
3) While all the cells are in haploid (n) condition only the polar nucleus is diploid (2n). This is due to the fusion of two nuclei.
4) The synergids are also known as helper cells.
5) After pollination pollen grain received by stigma, germinate and give rise to pollen tubes. The pollen tube has two male nuclei.
6) Usually the pollen tube enters the ovule through microphyle and discharges the two male gametes into the embryo sac.
7) One male nucleus (gamet) approaches the egg and fuse with it to form diploid (2n) zygote this is called first fertilization.
8) The other male nucleus reaches the secondary nucleus (2n) (polar nucleus) and fuses with it to form endosperm nucleus which will be triploid. This is second fertilization. Thus double fertilizatio occurs in embryosac.
Changes after double fertilization :
9) After double fertilization, the ovule increases in size rapidly as a result of formation of endosperm tissue by mitosis and the development of new embryo.
10) The embryo consists of cotyledons as epicotyl and a hypocotyl. The cotyledons become greatly enlarged because of stored food for the seedling.
11) The zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is converted into a seed. The ovary grows to form a fruit.