Central Topic: Sexual Reproduction in Flowering Plants

Sexual Reproduction in Flowering Plants
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├── FLOWER STRUCTURE
│   ├── Calyx (sepals) — protective
│   ├── Corolla (petals) — attractive
│   ├── Androecium (stamens) — male
│   │   ├── Filament (stalk)
│   │   └── Anther $\frac{4 pollen sacs}{microsporangia}$
│   └── Gynoecium (pistils) — female
│       ├── Stigma (receives pollen)
│       ├── Style (pollen tube grows here)
│       └── Ovary (contains ovules)
│
├── MALE GAMETOPHYTE (Pollen)
│   ├── Microsporogenesis: PMC (2n) → meiosis → tetrad (n)
│   ├── Pollen grain: vegetative cell + generative cell
│   ├── Pollen wall: Exine (sporopollenin) + Intine (cellulose)
│   └── Germ pores: no sporopollenin; pollen tube emerges here
│
├── FEMALE GAMETOPHYTE (Embryo Sac)
│   ├── Megasporogenesis: MMC (2n) → meiosis → 4 megaspores (3 degenerate)
│   ├── Embryo sac development: 1 megaspore → 3 mitoses → 7 cells, 8 nuclei
│   ├── Micropylar end: egg (n) + 2 synergids (n each)
│   ├── Central: central cell (2 polar nuclei, each n)
│   └── Chalazal end: 3 antipodals (n each)
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├── POLLINATION
│   ├── Autogamy (same flower) — no variation
│   ├── Geitonogamy (same plant) — genetically self; ecologically cross
│   ├── Xenogamy (different plants) — true cross-pollination; variation
│   ├── Outbreeding Devices
│   │   ├── Self-incompatibility
│   │   ├── Dicliny (unisexual flowers)
│   │   └── Dichogamy (different maturation times)
│   └── Pollination Agents
│       ├── Wind (anemophily) — light pollen, feathery stigma
│       ├── Insects (entomophily) — sticky pollen, bright petals, nectar
│       ├── Water (hydrophily) — mucilaginous pollen
│       ├── Birds (ornithophily) — bright red/orange, copious nectar
│       └── Bats (chiropterophily) — nocturnal, strong scent
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├── DOUBLE FERTILIZATION (unique to angiosperms)
│   ├── Syngamy: sperm + egg → zygote (2n)
│   └── Triple fusion: sperm + 2 polar nuclei → PEN (3n)
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├── POST-FERTILIZATION
│   ├── Zygote → embryo (2n): globular → heart → torpedo → mature
│   ├── PEN → endosperm (3n): nutritive tissue
│   ├── Ovule → seed
│   ├── Integuments → seed coat (testa + tegmen)
│   ├── Ovary → fruit
│   └── Ovary wall → pericarp
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└── SPECIAL REPRODUCTION MODES
    ├── Apomixis: seeds without fertilization (clones)
    ├── Parthenocarpy: seedless fruit without fertilization
    └── Polyembryony: multiple embryos in one seed (Citrus)