Dioecious: Separate sexes (e.g., humans, papaya).

2. Sexual Reproduction in Flowering Plants

Flower: Reproductive unit.
- Androecium (Male): Stamens (Filament + Anther). Anther has microsporangia.
- Gynoecium (Female): Pistil/Carpel (Stigma + Style + Ovary). Ovary has ovules.
Pre-fertilisation:
- Microsporangium & Pollen Grain:
  - Microsporangium (pollen sac) contains sporogenous tissue $\to$ Microspore Mother Cells (MMC) $\to$ Meiosis $\to$ Microspores (pollen tetrad) $\to$ Pollen Grains.
  - Pollen grain: Two-layered wall (Exine - sporopollenin, Intine - pectin & cellulose). Two cells: Vegetative cell (large), Generative cell (small).
- Megasporangium (Ovule) & Embryo Sac:
  - Ovule attached to placenta by funicle. Contains nucellus (nutritive).
  - Megaspore Mother Cell (MMC) in nucellus $\to$ Meiosis $\to$ 4 megaspores (usually 1 functional).
  - Functional megaspore $\to$ 3 mitotic divisions $\to$ 8-nucleate, 7-celled Embryo Sac (Female Gametophyte).
  - Structure of Embryo Sac: Egg apparatus (1 egg cell, 2 synergids), 3 antipodal cells, 1 central cell (2 polar nuclei).
- Pollination: Transfer of pollen grains from anther to stigma.
  - Self-pollination (Autogamy, Geitonogamy).
  - Cross-pollination (Xenogamy).
  - Agents: Wind (Anemophily), Water (Hydrophily), Animals (Zoophily - insects, birds, bats).
- Pollen-Pistil Interaction: Chemical dialogue leading to pollen germination on stigma. Pollen tube grows through style to ovule.
Fertilisation: (Double Fertilisation - unique to angiosperms)
- Pollen tube releases 2 male gametes into embryo sac.
- Syngamy: One male gamete + Egg cell $\to$ Zygote ($2n$).
- Triple Fusion: Other male gamete + 2 polar nuclei $\to$ Primary Endosperm Nucleus (PEN, $3n$).
Post-fertilisation:
- Zygote $\to$ Embryo.
- PEN $\to$ Endosperm (nutritive tissue).
- Ovule $\to$ Seed.
- Ovary $\to$ Fruit.
- Ovary wall $\to$ Pericarp (fruit wall).
Seed: Contains embryo and food reserves. Non-albuminous (no residual endosperm, e.g., pea, groundnut) or Albuminous (endosperm present, e.g., wheat, maize).
Apomixis: Seed formation without fertilisation (e.g., citrus, mango).
Polyembryony: Occurrence of more than one embryo in a seed (e.g., citrus).

3. Human Reproduction

Male Reproductive System:
- Primary sex organ: Testes (produce sperm & testosterone).
- Accessory ducts: Rete testis, Vasa efferentia, Epididymis, Vas deferens, Ejaculatory duct, Urethra.
- Accessory glands: Seminal vesicles, Prostate gland, Bulbourethral glands (produce seminal plasma).
- External genitalia: Penis, Scrotum.
Female Reproductive System:
- Primary sex organ: Ovaries (produce ova & female hormones).
- Accessory ducts: Oviducts (fallopian tubes), Uterus (womb), Vagina.
- External genitalia: Mons pubis, Labia majora, Labia minora, Hymen, Clitoris (Vulva).
- Mammary glands: For lactation.
Gametogenesis: