Lesson 6: Angiosperm Reproduction

  • Reproduction Importance: Essential for species perpetuation.

  • Learning Objectives: Review objectives prior to lessons.

  • Floral Evolution:

    • Floral organs evolved from leaves.

    • Modern angiosperms have four distinct whorls:

    • A complete flower has all four whorls.

    • An incomplete flower lacks one or more whorls.

    • Floral modifications are enhanced by natural selection for pollination traits.

  • Floral Parts:

    • Calyx: Outermost whorl; protects flower bud.

    • Corolla: Attracts pollinators.

    • Androecium: Male structures, collective term for stamens (stalk or filament and anther containing microspore mother cells).

    • Gynoecium: Female parts; consists of one or more carpels containing ovules.

    • Style connects to pollen-receptive stigma.

  • Floral Trends:

    • Trends include fusion of flower parts and reduction in number of parts.

    • Bilateral symmetry is more advanced than radial symmetry.

    • Example: Orchids (bilateral symmetry, fused petals) vs. wild geraniums (five petals, ten stamens).

  • Alternation of Generations:

    • Characteristics of all plants; lifecycle includes sporophyte (flower) and small gametophytes.

    • Micro gametophytes: Pollen grains (male).

    • Mega gametophytes: Embryo sac (female).

  • Pollen Formation:

    • Inside anther: Microspore mother cells undergo meiosis to form microspores.

    • Microspores develop into pollen grains (tube cell + generative cell, which forms two sperm).

  • Embryo Sac Formation:

    • Inside ovule: Megaspore mother cell undergoes meiosis, resulting in four megaspores (three disintegrate).

    • Surviving megaspore forms a seven-celled, eight-nucleate embryo sac.

  • Pollination:

    • Transfer of pollen to stigma; types include self-pollination and cross-pollination.

    • Self-Pollination: Pollen from same flower/plant; promotes genetic similarity.

    • Cross-Pollination: Involves different individuals; promotes genetic variation.

    • Monoecious: Separate male/female flowers on the same plant.

    • Dioecious: Male and female flowers on different plants.

    • Self-Incompatibility: Blocks pollen tube growth to promote outcrossing.

  • Co-evolution of Pollinators and Flowers:

    • Specialized flowers attract specific pollinators, creating mutual relationships.

  • Double Fertilization:

    • Unique to angiosperms; results in a diploid zygote and triploid endosperm after fertilization.

    • Pollen tube grows down style to ovary for fertilization.

  • Seed and Fruit Development:

    • Seed coat forms from ovule's outer coverings.

    • Ovary develops into fruit, aiding seed dispersal.

    • Fruit types based on pericarp characteristics (fleshy vs dry).

  • Dispersal Strategies:

    • Methods including ingestion by animals, attachment to fur, wind dispersal, and water dispersal.

  • Asexual Reproduction:

    • Mechanism for producing genetically identical offspring, advantageous in harsh conditions.

    • Includes apomixes and vegetative reproduction via runners, rhizomes, or root sprouts.