Double fertilization in angiosperms — explain with diagram

After pollination, the pollen tube grows through the style and enters the ovule through the micropyle. The pollen tube carries two male gametes (sperm cells) into the embryo sac.

The embryo sac (female gametophyte) is a 7-celled, 8-nucleate structure containing: 1 egg cell, 2 synergids, 3 antipodal cells, and a large central cell with 2 polar nuclei.

Inside the embryo sac, two separate fusion events happen simultaneously:

Syngamy (first fertilization): One male gamete ($n$) fuses with the egg cell ($n$) to form the zygote ($2n$). This zygote will develop into the embryo.

Triple fusion (second fertilization): The other male gamete ($n$) fuses with the two polar nuclei ($n + n$) in the central cell to form the Primary Endosperm Nucleus (PEN) ($3n$). This triploid nucleus will develop into the endosperm.

Since two fusion events occur in the same embryo sac, the process is called double fertilization. It is unique to angiosperms — no other plant group shows this.

• The zygote ($2n$) undergoes mitotic divisions to form the embryo (with radicle, plumule, and cotyledons).
• The PEN ($3n$) divides repeatedly to form the endosperm — a nutritive tissue that feeds the developing embryo.
• The ovule develops into the seed (seed coat from integuments).
• The ovary develops into the fruit (fruit wall from ovary wall).