Seedless Plants I Notes

q111Land Plant Origins

  • Derived from Archaeplastida: Chlorophytes and Charophytes.

  • Streptophytes include Charophytes, Embryophytes (Land Plants), Tracheophytes (Vascular Plants), Euphyllophytes, and Spermatophytes (Seed Plants).

  • Charophytes are multicellular, photoautotrophic protists, the closest living relatives to land plants, living in freshwater environments.

Challenges of Terrestrial Life

  • Desiccation:

    • Waxy cuticle: Impermeable to water but limits gas exchange.

    • Stomata: Openings for gas exchange.

    • Mycorrhizal associations: Symbiotic relationship with fungi for nutrient availability.

  • Transport:

    • Xylem: Movement of water.

    • Phloem: Movement of food and hormones.

  • UV Radiation:

    • Minimize mutation effects via diploidy; plants tend to have large, polyploid genomes.

Haplodiplontic Life Cycle

  • Both diploid and haploid life stages undergo mitosis.

    • Sporophyte: Diploid, produces spores via meiosis.

    • Gametophyte: Haploid, produces gametes via mitosis.

    • Sporangia: Spore-producing cells.

    • Gametangia: Gamete-forming cells.

  • Reduction of gametophyte stage correlated with increased terrestrial specialization.

Bryophytes

  • Dominant gametophyte generation, earliest land plants.

    1. Tied to water, limited ability to regulate internal water, tolerate desiccation.

    2. Limited nutrient transport through cells (no vascular tissue).

    3. Photosynthetic gametophytes, sporophytes directly attached to gametophytes.

Three Main Groups of Bryophytes

  1. Liverworts (Phylum Hepaticophyta)

    • Flattened gametophytes with liver-like lobes.

    • Rhizoid: Root-like structures aid in absorption, anchors to substrate.

    • Air chambers for gas exchange (not stomata; cannot close).

  2. Mosses (Phylum Bryophyta)

    • Leaf-like gametophytes with rhizoid and midrib (stem-like axis).

    • "Leaf": One cell thick, photosynthetic.

    • Capsule: Sporangia with stoma; spores.

    • Gametophyte is dominant life stage; sporophyte is not photosynthetic, attached to gametophyte.

    • Archegonia: Female gametophyte.

    • Antheridia: Male gametophyte.

    • Sperm is flagellated and swims to egg in water for fertilization.

    • Archegonium: Single haploid egg via mitosis.

    • Antheridium: Many haploid sperm via mitosis.

    • Fertilized zygote develops within archegonium and forms sporophyte.

  3. Hornworts (Phylum Anthocerotophyta)

    • Sister-group to tracheophytes (vascular plants), has stomata for gas exchange.

    • Morphologically similar to liverworts, but sporophyte is a photosynthetic horn.

    • Sporophyte has hornwort stoma.