REP-01 — Concise 10-Sentence Overview — Summary

Sexual reproduction in angiosperms begins in the flower's androecium, where pollen mother cells (2n) undergo meiosis to form haploid pollen grains — the male gametophyte.
The pollen grain wall has a sporopollenin-containing exine (outer, resistant) and a cellulose intine (inner, forms pollen tube); germ pores are exine-free zones for tube emergence.
In the gynoecium, the megaspore mother cell (2n) undergoes meiosis to produce four megaspores, of which three degenerate and one develops into the seven-celled, eight-nucleate embryo sac.
The embryo sac contains the egg apparatus (egg + 2 synergids with filiform apparatus) at the micropylar end, the central cell (2 polar nuclei) in the middle, and three antipodals at the chalazal end.
Pollination types are: autogamy (same flower), geitonogamy (same plant — genetically self, no variation), and xenogamy (different plants — genetic variation); outbreeding devices (self-incompatibility, dicliny, dichogamy) promote xenogamy.
After pollination, the pollen tube grows through the style, enters the embryo sac via the micropyle and synergid, and releases two sperm cells.
Double fertilization — unique to angiosperms — involves syngamy (sperm + egg = 2n zygote) and triple fusion (sperm + 2 polar nuclei = 3n PEN) occurring simultaneously.
Post-fertilization: zygote → embryo (2n); PEN → endosperm (3n — triploid, the single most tested fact); ovule → seed; ovary → fruit; integuments → seed coat.
The endosperm is always triploid (3n) in angiosperms — formed by triple fusion — a fact that distinguishes it from the diploid zygote/embryo.
Special reproductive modes include apomixis (seeds without fertilization — agricultural importance for hybrid vigor), parthenocarpy (seedless fruits — banana), and polyembryony (multiple embryos per seed — Citrus).