Lesson 06: Angiosperm Reproduction

Lecture Notes

1. Describe the Structure of a Complete Flower

• Floral Organ Evolution: Derived from modified leaves.

• Four Whorls of a Flower:

  • Calyx – Outermost, protects the flower bud.

  • Corolla – Petals attract pollinators.

  • Androecium – Male reproductive structures (stamens: filament + anther).

  • Gynoecium – Female reproductive structures (carpels: ovary, style, stigma).

• Floral Modifications & Evolution:

  • Fusion and reduction of floral parts.

  • Bilateral symmetry (e.g., orchids) more advanced than radial symmetry.

2. Distinguish Between Microgametophytes and Megagametophytes

• Alternation of Generations:

  • Sporophyte Generation – Dominant, includes the flower.

  • Gametophyte Generation – Small, contained within sporophyte.

• Types:

  • Microgametophytes (Male Gametophytes):

    • Pollen grains

    • Develops from microspore

    • Located inside the anther

    • Produces sperm cells for fertilization

    • Pollen grain: Tube cell and generative cell

  • Megagametophytes (Female Gametophytes): Embryo sac within the ovule.

    • Develops from megaspore

    • Located inside the ovule

    • Houses the egg and supports fertilization

• Pollen is the land plant innovation that allows sperm to travel to the egg without swimming in water.

3. Describe the Co-Evolution Between Flowers and Pollinators

• Mutualism: Flowers provide food (nectar, pollen), pollinators aid reproduction.

• Adaptations for Pollinators:

  • Bees – Attracted to yellow/blue flowers, guided by shape.

  • Hummingbirds – Prefer red, tubular flowers.

  • Butterflies – Use proboscis for tiny tubular flowers.

  • Moths & Bats – Nocturnal, attracted to light-colored flowers.

• Wind Pollination: No need for showy petals, common in trees like birch.

4. Discuss the Advantages and Disadvantages of Selfing vs. Outcrossing

• Pollen transfer to the stigma is defined as pollination

• Self-Pollination (Selfing):

  • Advantages:

    • Ensures reproduction when pollinators are scarce.

    • Genetically similar offspring thrive in stable environments.

  • Disadvantages:

    • Reduces genetic diversity.

• Cross-Pollination (Outcrossing):

  • Advantages:

    • Increases genetic variation, promotes adaptation.

  • Mechanisms Promoting Outcrossing:

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

    • Dioecious species – Male and female flowers on different plants.

    • Dichogamy – Male and female structures mature at different times.

    • Self-Incompatibility – Pollen tube growth blocked if genetically related.

5. Describe the Unique Features of Double Fertilization

• Double Fertilization: Fertilization of the egg to form a diploid zygote and union of the second sperm with the polar nuclei to form triploid endosperm.

• Unique to Angiosperms.

• Two Sperm Involved:

  • 1 sperm + egg → Zygote (diploid embryo).

  • 1 sperm + polar nuclei → Endosperm (triploid, nutrient tissue).

• Pollen Tube Formation: Tube cell grows down the style to the ovule.

6. Describe the Development of the Ovule into a Seed

• Zygote Development:

  • Undergoes mitosis, forms embryo.

  • Suspensor links embryo to nutrient supply.

• Seed Components:

  • Food Reserves: Starches, lipids, proteins.

  • Seed Coat: Protective covering from ovule tissues.

• Dormancy: Ensures survival until favorable conditions arise.

7. Describe the Development of the Ovary into the Fruit and Features of the Pericarp That Aid in Dispersal

• Fruit = Mature Ovary/Carpel.

• Pericarp Layers (Influence Fruit Type):

  • Fleshy Fruits: Tomato (entire pericarp fleshy), peach (skin, flesh, pit).

  • Dry Fruits: Legumes, samaras.

  • Aggregate Fruits: Strawberry (from multiple ovaries of one flower).

  • Multiple Fruits: Pineapple (from fused ovaries of multiple flowers).

• Dispersal Mechanisms:

  • Animal Ingestion – Red/black fruits, seeds excreted far away.

  • Attachment to Animals – Burrs, spines stick to fur.

  • Wind Dispersal – Dandelion parachutes, winged samaras.

  • Water Dispersal – Coconut floats to new islands.

• The food supply is critical to embryo survival because the development of photosynthetic tissue is triggered by light and it's not functional immediately after germination.

• Food reserves: starches, lipids, and proteins

• Fruit development is coordinated with seed maturation by the hormone auxin

• When seeds are mature, the hormone ethylene will trigger ripening of fleshy fruits.

8. Describe Asexual Reproduction and Provide Examples

• Apomixis: Asexual seed production (genetically identical offspring).

• Vegetative Reproduction: from vegetative tissues

  • Runners & Rhizomes – Horizontal stems giving rise to new plants.

  • Suckers – Root sprouts forming new plants.

  • Adventitious Plantlets – Form on leaves, fall off, and root.

• Somatic Embryogenesis: Embryo development from non-reproductive tissue.

Review:

• Double fertilization

• mega vs. Micro gametophytes (concept; what is it?)

• This figure from the HW

  

Class Notes

Sexual Reproduction

• A complete flower has both male and female parts

• Angiosperm reproduction

  • Sporophyte—>pollen grows into the microgametophyte “pollen tube”

  • Pollen tube + embryo sac = Gametophyte

Pollination

• Types:

  • Wind

  • Animals

• Attraction

  • Smell—flies

  • Sweet odor— bees

  • Color

  • Pattern —(U.V reflection)

  • Shape

Seed Dispersal

• Animals—> eat fruit

  • Scatterm hoarding

• By sea

Figures