Plant Reproduction Notes

Parts of a Flowering Plant

• Reproductive Structures:
  • Male (Stamen):
    • Anther: Produces pollen.
    • Filament: Supports the anther.
  • Female (Carpel):
    • Stigma: Receives pollen.
    • Style: Connects the stigma to the ovary.
    • Ovary: Contains ovules.
• Non-reproductive Parts:
  • Petals: Often colorful to attract pollinators.
  • Sepals: Protect the flower bud before it blooms.
  • Receptacle: Supports the flower on the plant.

Pollination

• Self-Pollination: Pollen from the anther lands on the stigma of the same flower or plant.
• Cross-Pollination: Pollen from one plant reaches the stigma of another plant.

Self-Pollination Vs Cross-Pollination

• Diagram illustrating pollen transfer from anther to stigma in both self-pollination and cross-pollination scenarios.

Consequences/Implications of Self-Pollination

• Advantages:
  • Reliable Reproduction: No need for external agents, ensuring consistency.
  • Energy Efficiency: Reduced investment in attracting pollinators.
  • Maintains Genetic Stability: Preserves the parent's genetic makeup.
  • Adaptability in Sparse Populations: Useful when other plants or pollinators are scarce.
• Disadvantages:
  • Reduced Genetic Variation: Offspring are genetically identical, limiting adaptability.
  • Inbreeding Depression: Accumulation of harmful recessive traits.
  • Limited Evolutionary Potential: Reduced ability to adapt over time.

Cross-Pollination Advantages & Disadvantages

• Advantages:
  • Genetic Diversity: Combines genetic material for better adaptation.
  • Healthier Offspring: Promotes hybrid vigor (heterosis) and disease resistance.
  • Evolutionary Benefits: Facilitates natural selection and development of new traits.
• Disadvantages:
  • Dependence on Pollinators: Requires external agents which may be unreliable.
  • Energy-Intensive: Requires resources for attractive flowers and pollen production.
  • Uncertainty in Pollination: Success depends on environmental factors and pollinator availability.
  • Wastage: Significant pollen loss may occur.

Insect vs. Wind Pollination

• Feature Comparison:
  • Flowers:
    • Insect Pollination: Bright, colorful, fragrant, with nectar.
    • Wind Pollination: Small, dull, no scent or nectar.
  • Pollen:
    • Insect Pollination: Sticky and heavy.
    • Wind Pollination: Light and powdery.
  • Pollen Production:
    • Insect Pollination: Moderate amounts.
    • Wind Pollination: Large quantities.
  • Stigma:
    • Insect Pollination: Sticky.
    • Wind Pollination: Large, feathery.

Fertilization

• Definition: Fusion of the male gamete (from pollen) with the female gamete (in the ovule) to form a zygote.

Fertilization Process

• Pollen grain lands on the stigma and germinates.
• A pollen tube grows down through the style towards the ovary.
• The pollen tube reaches the ovule through the micropyle.
• Male gametes (sperm cells) are carried to the embryo sac inside the ovule.
• One male gamete fuses with the egg cell to form a zygote.
• The zygote develops into an embryo.

Post Fertilization

• The zygote develops into an embryo.
• The ovule transforms into a seed.
• The ovary matures into a fruit.
• Other floral parts wither away.

The Seed

• Seed Structure:
  • Embryo: Includes the shoot (plumule) and root (radicle).
  • Food Store: Provides nutrients (e.g., cotyledons or endosperm).
  • Seed Coat (Testa): Protects from damage, dehydration, and disease.

Seed Germination

• Conditions for Germination:
  • Water: Activates enzymes, softens the seed coat, and aids metabolic processes.
  • Oxygen: Required for cellular respiration.
  • Temperature: Must be suitable for enzyme activity.
• Stages of Germination:
  • Absorption of water (imbibition).
  • Enzyme activation and digestion of stored food.
  • Emergence of the root (radicle) and shoot (plumule).

Investigation on Seed Germination

• Description of an experiment involving cress seeds in tubes (A, B, C, and D) with varying conditions (layer of oil, dry cotton wool, moist cotton wool, boiled and cooled water) to investigate the requirements for seed germination.