Angiosperm Life Cycle Overview and Flower Structure

Life Cycle Stages

• Adult Mature Sporophyte: Dominant phase.
• Flower Production: For sexual reproduction.
• Gametophytes: Produced on flowers, facilitating pollination and fertilization.
• Post-Fertilization: Formation of diploid zygote, development into diploid embryo, seed maturation, and dispersal.

Flowering and Genetic Expression

• Flower Formation: Derived from modified leaves (sporophylls).
• Gene Expression: Changes in gene expression lead to flower development.
• Environmental Cues: Temperature and sunlight influence flowering timing.
• Developmental Stage: Flowering occurs when plant resources can support reproduction.
• Hormonal Triggers: Hormones initiate the development of flowers from leaves.

Floral Structure

• Four Floral Organs (Whorls):
  • Calyx: Outermost whorl.
  • Corolla: Inside calyx.
  • Androecium: Inside corolla.
  • Gynoecium: Center-most part.
• Variation and Functionality: Designed for specific pollinators, may have fused or reduced parts.

Flower Types and Symmetry

• Perfect Flowers: Contain both stamens and carpels (hermaphroditic).
• Imperfect Flowers: Contain either stamens or carpels.
  • Monoecious: Both male and female flowers on the same plant.
  • Dioecious: Male and female flowers on separate plants.
• Symmetry:
  • Radial Symmetry: Uniform appearance.
  • Bilateral Symmetry: Distinct sides, evolutionary trend towards increased bilateral symmetry for potential functional benefits.

Inflorescences

• Single Flower: One flower per stem attachment.
• Inflorescence: Multiple flowers grouped to appear as one (e.g., sunflowers, daisies).
  • Disc Flowers: Central, no petals.
  • Ray Flowers: Peripheral, produce petals.

Gametophyte Formation

• Female Side (Carpel):

  • Ovary: Contains chambers with ovules and megasporangia.
  • Megasporocytes: Undergo meiosis to produce megaspores.
  • Megagametophyte (Embryo Sac):
    • Develops from surviving megaspore.
    • Consists of eight nuclei, seven cells (e.g., central cell with polar nuclei, egg cell).

• Male Side (Stamen):

  • Anther: Contains microsporangia with microsporocytes.
  • Microgametophyte (Pollen Grain):
    • Develops from microspores.
    • Two cells: generative (produces sperm) and tube (grows pollen tube).

Upcoming Topics

• In-depth exploration of pollination and fertilization processes in the next session.