Angiosperm Reproduction and Biotechnology Notes

Angiosperm Reproduction and Biotechnology

Chapter 38 Overview

  • Angiosperms, or flowering plants, are a key group in terrestrial ecosystems and crucial for agriculture.
  • Artificial selection and genetic engineering have allowed humans to modify angiosperms into important crop species.

CONCEPT 38.1: Flowers, Double Fertilization, and Fruits

  • Angiosperm life cycles feature alternation between sporophyte (2n) and gametophyte (n) generations.
  • Sporophytes produce haploid spores via meiosis; spores develop into gametophytes through mitosis.
  • Gametophytes produce gametes (sperm and eggs) via mitosis.
  • In angiosperms, the sporophyte generation is dominant.
  • The angiosperm lifecycle is characterized by flowers, double fertilization, and fruits (the three Fs).

Flower Structure and Function

  • Flowers are reproductive shoots attached to the stem via the receptacle.
  • Floral organs: carpels, stamens, petals, and sepals.
  • Stamens and carpels are sporophylls (specialized leaves for reproduction), while sepals and petals are modified sterile leaves.
  • Color and odor attract pollinators.

Methods of Pollination

  • Pollination is the transfer of pollen from anthers to stigma.
  • Occurs via wind (20%), water, or animals (bees 65%, moths, butterflies, flies, bats, birds).
  • Wind-pollinated species release large quantities of small pollen grains.
  • Many angiosperms rely on animals for pollen transfer.

The Angiosperm Life Cycle: An Overview

  • Gametophyte development.
  • Sperm delivery via pollen tubes.
  • Double fertilization.
  • Seed development.

Double Fertilization

  • Fertilization occurs after two sperm reach the female gametophyte.
  • One sperm fertilizes the egg, forming a zygote (2n).
  • The other sperm fuses with two polar nuclei, creating a triploid (3n) endosperm (food-storage tissue).
  • This ensures endosperm develops only in fertilized ovules.

Seed Development

  • After double fertilization, each ovule becomes a seed while the ovary develops into a fruit assisting in dispersal.
  • A germinating seed leads to a new sporophyte.
  • A mature seed contains a dormant embryo, stored food, and protective layers.

Fruit Structure and Function

  • The fruit is the mature ovary.
  • It protects enclosed seeds and aids in dispersal.
  • Fruit development is triggered by hormonal changes after fertilization.
  • The ovary wall can dry out or remain fleshy.

Fruit Classification

  • Simple fruits: Develop from a single carpel or fused carpels.
  • Aggregate fruits: Develop from a single flower with multiple separate carpels.
  • Multiple fruits: Develop from a group of flowers (inflorescence).
  • Accessory fruits: Contain other floral parts besides the ovary.
  • Ripening typically coincides with seed development completion.
  • Dry fruits undergo tissue aging and drying.
  • Fleshy fruits change color and produce sugars to attract animal dispersers.
  • Seed dispersal reduces competition with the parent plant.

CONCEPT 38.2: Sexual vs. Asexual Reproduction

  • Asexual reproduction: Offspring from a single parent, resulting in a clone (genetically identical).
  • Common in angiosperms.

Mechanisms of Asexual Reproduction

  • Fragmentation: Separation of parent plant parts that develop into new plants.
  • Adventitious shoots: Root systems giving rise to separate shoot systems.
  • Apomixis: Asexual production of seeds from a diploid cell (e.g., dandelions), allowing for cloning and seed dispersal.

Advantages and Disadvantages of Asexual and Sexual Reproduction

  • Asexual reproduction doesn't require pollinators or other individuals.
  • Asexual progeny are genetically identical to the parent, advantageous in stable environments.
  • Vegetative reproduction: Asexual progeny arise from mature fragments, making them resilient.
  • Large seed production compensates for low individual survival rates.
  • Lack of genetic variation in asexual reproduction makes plants vulnerable to environmental changes.
  • Sexual reproduction generates genetic variation, enabling evolutionary adaptation.
  • Seed production aids in long-distance dispersal.

Self-Fertilization Prevention

  • Some plants self-fertilize, reducing genetic diversity.
  • Many plants have mechanisms to prevent selfing, such as:
    • Separate staminate (lacking carpels) and carpellate (lacking stamens) flowers on different plants.
    • Stamens and carpels maturing at different times.
    • Spatial arrangement preventing contact between stamens and stigma.

Self-Incompatibility

  • Self-incompatibility: Plant rejects its own pollen or pollen from close relatives.
  • Analogous to animal immune response (rejection of self).
  • Recognition of