Plant Reproduction Notes

Plant Reproduction

Plant Life Cycle

  • Basic structure:

    • Gametes (pollen and embryos) meet.
    • Fertilization occurs, leading to embryo development.
    • Embryo grows into a seed (embryo + protective structure).
    • Seed germinates into a seedling.
    • Seedling grows into a plant (vegetative and reproductive stages).
    • Some plants (wheat) do this once, others (canola) repeatedly, perennials (apple trees) for decades.

  • Alternation of generations:

    • Sexual reproduction involves fertilization and meiosis (diploid to haploid, then back).
    • Plants undergo mitosis after meiosis, creating multicellular haploid structures.
    • Diploid stage: sporophyte (makes spores).
    • Haploid stage: gametophyte (makes gametes).

Flower Structures

  • Complete flowers have petals, sepals, stamen (male), and carpals (female).
    • Stamen: anther (holds pollen) + filament.
    • Carpels: ovary (with ovules), style, and stigma.
  • Incomplete flowers lack parts (e.g., eucalyptus without petals).
  • Perfect flowers: have both male and female parts.
  • Imperfect flowers: only male or female parts.
  • Monoecious: male and female flowers on the same plant (e.g., zucchini).
  • Dioecious: male and female flowers on separate plants (e.g., cannabis).
  • Grasses:
    • Inflorescence with spikelets containing florets (equivalent to flowers).
      • Number of florets determines grain yield.
    • Protective layers: glumes, palea, and lemma.

Pollination and Fertilization

  • Pollen:
    • Contains male gametes (sperm cells).
    • Structure varies by plant.
  • Ovules:
    • In the ovary and contain female gametes (egg cells).
  • Pollen lands on the sticky stigma, germinates, and grows pollen tubes down the style.
  • Double fertilization (angiosperms):
    • Two sperm cells travel down the pollen tube.
    • One fertilizes the egg cell (zygote).
    • The other fertilizes the central cell (endosperm - food source for the seed).

Seeds and Germination

  • Seeds develop from ovules.
    • Functions: protection, food reserves (endosperm), dispersal, dormancy.
  • Seed structure: embryo, seed coat (tester), cotyledons (embryonic leaves), radicle (embryonic root).
  • Fruits: enlarged ovaries, aid in dispersal (wind, water, animals).
  • Germination: seed grows into a plant when conditions are suitable (water, oxygen, temperature, light).
    • First, the root emerges and grows down.
    • Then the cotyledons emerge.
    • Epigeal germination: cotyledons emerge above ground.
    • Hypogeal germination: cotyledons remain below ground.
  • Cotyledons: nourish the developing plant.

Dormancy

  • Mechanism to prevent germination in unsuitable conditions.
    • Ensures seeds don't all germinate at once.
    • Can last days, weeks, months, or years.
    • Dormant seeds are hard to kill; need to be germinating for herbicides to work.