REP-01 — 20 Essential NEET Facts — Summary

A typical angiosperm flower has four whorls (outer to inner): calyx, corolla, androecium, gynoecium.
Pollen grain wall: exine (outer, sporopollenin) and intine (inner, cellulose/pectin).
Sporopollenin is the most resistant biological material — resists heat, strong acids, alkalis, and enzymes.
Germ pores are exine-free regions through which the pollen tube (intine) emerges.
Mature pollen grain: two-celled — vegetative cell (tube nucleus) + generative cell.
PMC (2n) undergoes meiosis → microspore tetrad (each n) → pollen grain.
MMC (2n) undergoes meiosis → 4 megaspores; 3 degenerate, 1 functional survives.
Functional megaspore → 3 free nuclear mitotic divisions → 8 nuclei → 7 cells, 8 nuclei (embryo sac).
Embryo sac composition: egg (1) + synergids (2) at micropylar end; central cell (2 polar nuclei); antipodals (3) at chalazal end.
Synergids have the filiform apparatus — guides pollen tube chemotropically.
Geitonogamy: ecologically cross-pollination, genetically self-pollination — NO genetic variation.
Xenogamy: true cross-pollination between different plants — introduces genetic variation.
Outbreeding devices: self-incompatibility, dicliny (unisexual flowers), dichogamy (different maturation times).
Double fertilization = syngamy (sperm + egg = zygote, 2n) + triple fusion (sperm + 2 polar nuclei = PEN, 3n).
Double fertilization is UNIQUE to angiosperms.
ENDOSPERM IS TRIPLOID (3n) — the single most tested NEET fact in this chapter.
Post-fertilization: ovule → seed; ovary → fruit; integuments → seed coat; PEN → endosperm; zygote → embryo.
Embryo development stages: globular → heart → torpedo → mature.
Apomixis = seeds without fertilization (clone offspring, agricultural value for preserving hybrid vigor).
Parthenocarpy = seedless fruit without fertilization (banana); polyembryony = multiple embryos/seed (Citrus).