Angiosperm Reproduction and Development Notes

Angiosperm Reproduction
  • Flower Structure
    • Parts of an Idealized Flower:
    • Stamen: Male reproductive part; consists of
      • Anther: Produces microspores that become pollen grains.
      • Filament: Supports the anther.
    • Carpel: Female reproductive part; includes
      • Stigma: Receives the pollen.
      • Style: Connects stigma to ovary.
      • Ovary: Contains ovules, which develop into seeds after fertilization.
    • Other Parts:
    • Petal: Attracts pollinators.
    • Sepal: Protects the flower bud.
    • Receptacle: Attachment point for flower parts.
Angiosperm Life Cycle
  • Key Lifecycle Stages:
    • Sporophyte (2n): The mature plant.
    • Gametophyte Development:
    • Microspore Mother Cell (2n): Located in pollen sacs of anthers.
    • Undergoes meiosis to produce a pollen tetrad of 4 microspores (n).
    • Each microspore undergoes mitosis, forming a pollen grain with a tube cell and a generative cell.
      • Tube Cell: Forms the pollen tube.
      • Generative Cell: Forms 2 sperm cells, making a total of 3 cells in male gametophyte.
    • Ovule Development:
      • Each ovule contains a megaspore mother cell (2n) that undergoes meiosis to produce 4 megaspores (n).
      • Only one megaspore is functional; it undergoes mitosis, forming the embryo sac.
        • Embryo Sac Includes:
        • 1 Egg
        • 1 Central Cell with 2 Polar Nuclei
        • 5 Other Cells
        • Total: 7 cells, 8 nuclei (female gametophyte).
Fertilization Process
  • Germination of Pollen:
    • Pollen grain germinates on the stigma, forming a pollen tube.
    • Sperm cells travel down the tube.
    • Fertilization:
      • One sperm fertilizes the egg, forming a zygote that becomes the embryo.
      • The other sperm joins with the two polar nuclei, forming a triploid endosperm (3n), which serves as a food source for the developing embryo.
    • The ovule becomes a seed (composed of the embryo, endosperm, and seed coat), while the ovary develops into fruit.
Flower Anatomy
  • Receptacle: Form of stem attachment for the flower.
  • Calyx: Collective term for sepals.
  • Corolla: Collective term for petals.
  • Stamens: Male reproductive parts; include anther and filament.
  • Carpels: Female reproductive parts; consist of stigma, style, and ovary (megasporangium).
Fruit Development
  • Definition: Mature ovary.
  • Ovary Wall: AKA pericarp, consists of:
    • Exocarp: Skin of the fruit.
    • Mesocarp: Middle part, often fleshy.
    • Endocarp: Surrounds seeds, aids in protection and dispersal.
  • Types of Fruit:
    • Simple Fruits: Develop from one ovary.
    • Compound Fruits: Develop from several ovaries.
    • Aggregate Fruits: Formed from a single flower with multiple ovaries (e.g., blackberries).
    • Multiple Fruits: Formed from the fusion of ovaries from several flowers (e.g., pineapples).
Examples of Fruits
  • Apple (Pome):
    • Structure: Endocarp, exocarp, mesocarp.
  • Tomato (Berry):
  • Strawberry (Achene): Aggregate-accessory fruit formed from an enlarged receptacle.
  • Peach (Drupe): A fleshy fruit with a stony endocarp.
  • Peanut (Legume): Grows from a flowering plant, pegs develop into pods containing seeds.
  • Maple (Samara): Winged fruit for wind dispersal.
  • Acorn (Nut): A hard-shelled fruit.
  • Corn (Grain): Seed (kernel) surrounded by a husk, part of the inflorescence in maize.
Key Terms
  • Haploid (n): Cells with one set of chromosomes.
  • Diploid (2n): Cells with two sets of chromosomes.
  • Zygote (2n): Fertilized egg that develops into an embryo.