Describe briefly the process of double fertilization in angiosperms.
Answers
Double Fertilization
Double fertilization is the process found in angiosperms in which out of the two male gametes released inside the embryo sac, one fuses with the egg cell (syngamy) and another fuses with secondary nucleus (triple fusion).
Release of Male gametes inside embryo sac→
The pollen tube passes through the style and enters the ovule through the micropyle (porogamy). It penetrates the nucellus and enters the embryo sac.
It enters into one synergid through filiform apparatus. The synergid provides moisture to the tip of the pollen tube due to which it bursts open, thereby releasing the male gametes inside the embryo sac.
The synergids direct one male gamete to the egg cell and another male gamete to the secondary nucleus. The synergids degenerate later.
Syngamy (First fertilization)
Out of the two male gametes, one unites with the egg cell(n) to form a diploid zygote(2n). This is called syngamy or first fertilization.
Triple fusion (Second fertilization)
The second male gamete (n) unites with the secondary nucleus (2n) to form a triploid (3n) primary endosperm nucleus (PEN).
Syngamy and triple fusion together represent double fertilization which is a characteristic feature seen in angiosperms.
Double fertilization is a complex fertilization mechanism of flowering plants (angiosperms). This process involves the joining of a female gametophyte (megagametophyte, also called the embryo sac) with two male gametes (sperm). It begins when a pollen grain adheres to the stigma of the carpel, the female reproductive structure of a flower. The pollen grain then takes in moisture and begins to germinate, forming a pollen tube that extends down toward the ovary through the style. The tip of the pollen tube then enters the ovary and penetrates through the micropyle opening in the ovule. The pollen tube proceeds to release the two sperm in the megagametophyte.