Sexual Reproduction in Flowering plants Handwritten Notes

Description

• female gametes resulting in the formation of seeds.
• Key Structures: Flowers are the reproductive structures of angiosperms.

2. Structure of a Flower

• Parts of a Flower:
  • Calyx: Composed of sepals; protects the flower bud.
  • Corolla: Composed of petals; attracts pollinators.
  • Androecium: Male reproductive part; consists of stamens.
    • Stamen: Filament and anther (produces pollen grains).
  • Gynoecium: Female reproductive part; consists of carpels (pistils).
    • Carpel: Stigma, style, and ovary (contains ovules).

3. Development of Male Gametophyte

• Microsporogenesis:
  • Occurs in the anthers.
  • Microsporangium: Pollen sacs where microspore mother cells (microsporocytes) undergo meiosis to form microspores.
• Microspore Development:
  • Each microspore develops into a pollen grain.
  • Pollen grain: Consists of two cells (generative cell and vegetative cell).
  • Pollen Tube Formation: Upon germination, pollen tube carries the male gametes to the ovule.

4. Development of Female Gametophyte

• Megasporogenesis:
  • Occurs in the ovary.
  • Megasporangium: Ovule where megaspore mother cell (megasporocyte) undergoes meiosis to form four megaspores.
• Megaspore Development:
  • Typically, one megaspore develops into the embryo sac (female gametophyte).
  • Embryo sac: Contains seven cells and eight nuclei, including one egg cell, two synergids, three antipodal cells, and two polar nuclei.

5. Pollination

• Definition: Transfer of pollen grains from the anther to the stigma.
• Types of Pollination:
  • Self-Pollination (Autogamy): Pollen from the same flower or another flower on the same plant.
  • Cross-Pollination (Xenogamy): Pollen from a flower on a different plant.
• Agents of Pollination:
  • Biotic Agents: Insects, birds, bats, etc.
  • Abiotic Agents: Wind, water.

  • Fertilization

    • Process:
      • Pollen grain lands on stigma and germinates.
      • Pollen tube grows through the style to the ovary.
      • Double Fertilization: Unique to angiosperms; involves two fertilization events.
        • One sperm nucleus fuses with the egg cell to form the zygote (2n).
        • Another sperm nucleus fuses with the two polar nuclei to form the triploid endosperm (3n).

    7. Post-Fertilization Events

    • Formation of Seed:
      • Zygote: Develops into the embryo.
      • Endosperm: Provides nourishment to the developing embryo.
      • Ovule: Develops into the seed.
    • Formation of Fruit:
      • Ovary: Develops into the fruit.
      • Pericarp: The wall of the fruit, which may be fleshy or dry.

    8. Seed and Fruit Dispersal

    • Importance: Prevents overcrowding and promotes colonization.
    • Methods:
      • Wind Dispersal: Lightweight seeds with wings or hairs.
      • Water Dispersal: Seeds with buoyant structures.
      • Animal Dispersal: Seeds with hooks or edible fruits.

    9. Significance of Sexual Reproduction

    • Genetic Variation: Promotes genetic diversity.
    • Adaptation: Enhances the ability of plants to adapt to changing environments.
    • Survival: Ensures the continuation of species through seed formation.