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Notes Name- Sexual Reproductionin Flowering plants
Subject – Biology
Class – 12th
Total Pages: 46 Pages
Total Size: 13 MB
File Format: PDF (Portable Document Format)
Language of the Notes: English
Format: PDF (Portable Document Format)
Notes Type: Handwritten Notes
Description
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.
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