Lecture Notes: Reproductive Strategies of Plants

Introduction

• Alternation of Generations: A reproductive strategy developed by early plants, still used by nonvascular plants today.
  • Sporophyte: Diploid cells with two sets of chromosomes.
  • Gametophyte: Haploid cells with one set of chromosomes.
• Vascular plants have evolved the alternation of generations model, with significant differences from nonvascular plants.

Nonvascular Plants

• Gametophyte Dominance: Mosses, hornworts, and liverworts.
  • Gametophytes produce sperm/eggs.
  • Sperm swims to egg if conditions are moist.
  • Fertilized egg grows into sporophyte, which produces spores.

Vascular Plants

• Sporophyte Dominance: Ferns, pine trees, morning glories.
  • Fungi produce spores that grow into gametophytes.
  • Gametophytes have male and female reproductive organs.
• Reproduction of Ferns:
  • Spores develop into small gametophytes.
  • Moist conditions allow sperm to fertilize eggs.
  • Produces visible sporophyte (fern).

Gymnosperms

• Evolutionary Change: Transition from spores to seeds.
  • Seeds bypass the gametophyte stage.
  • Allows reproduction without water.
• Types: Conifers, gingkos, cycads.
  • Reproductive structures are cones.
  • Male cones produce pollen; female cones contain ovules.
  • Fertilized ovules develop into seeds.
• Special Adaptations:
  • Lodgepole Pine: Seeds released only after exposure to fire.

Angiosperms

• Characteristics: Have seeds and flowers.
  • Flowers attract animals for pollination (mutualism).
• Reproductive Process:
  • Flowers contain gametophytes.
  • Pollination occurs with help from animals.
  • Fertilized ovules become seeds; ovary develops into fruit.
• Fruit Definition: Anything that develops from the ovary and contains seeds.

Fruit and Not a Fruit

• Examples:
  • Sandspur (Fruit) vs. Carrot (Not Fruit)
  • Dandelion Fluff (Fruit) vs. Celery (Not Fruit)
  • Zucchini (Fruit) vs. Strawberry (Not Fruit, seeds outside)

Importance of Fruits

• Helps with seed dispersal, reducing competition with parent plants.

Conclusion

• Vascular plants have complex reproductive strategies crucial for their survival and propagation.
• Angiosperms are particularly successful due to their advanced mechanisms for pollination and seed dispersal.