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Seedless Plants Lecture Review

Intro / Context

  • Lecture delivered informally (instructor notes sinus issues, heat wave, worm delivery) but content-dense; focus = “Seedless Plants” within a broader Botany unit.

  • Upcoming exam will cover: history of the world, botany, bacteria, viruses, protists → this lecture supplies seedless plant portion.

Ways Plants Can Be Classified (Instructor’s quick list)

  • Seed vs. spore reproduction
    • Seed = embryo + food supply + protective coat
    • Spore = single haploid cell; no food reserve

  • Vascular (can transport water via xylem/phloem) vs. non-vascular (mosses, liverworts). Non-vascular stay low like a “putting green.”

  • Flowering vs. non-flowering
    • Flowers/fruit evolved late; today dominate visible flora outside.

  • Woody vs. herbaceous
    • Woody = trees, shrubs; herbaceous = grasses, daisies, milkweed, etc.

  • Size range (microscopic → giant redwoods).

  • Invasive vs. native
    • Native = historically present in NY; invasive = introduced & aggressive (e.g., dandelion, Japanese knotweed, hogweed).
    • Personal anecdote: instructor removed ~½ acre of Japanese knotweed; hogweed causes severe burns; poison ivy is native but ubiquitous thanks to bird-dispersed fruit.

Where Did Plants Come From?

  • Evolved from green algae (chlorophyta), specifically charophytes.

  • Land colonization ≈ 475\ \text{million years ago} (Early Ordovician).
    • Motivated by “opportunity” – unoccupied sunlight & atmospheric CO₂.

Problems Faced Moving to Land

  1. Desiccation (drying out).

  2. Gravity (loss of buoyant support).

  3. Reproduction without water (how get sperm to egg?).

Advantages on Land

  • Abundant light, atmospheric \text{CO}_2, mineral nutrients (N, P, K), lack of herbivores & pathogens at first.

Defining Traits That Separate TRUE PLANTS From Other Algae

  1. Alternation of generations (distinct haploid gametophyte & diploid sporophyte).

  2. Spores produced in sporangia (water-tight structures).

  3. Gametes produced in gametangia (♂ antheridia, ♀ archegonia).

  4. Apical meristems – perpetual embryonic tissue at tips of shoots & roots allowing indeterminate growth.

  5. (Add-on) Cuticle – waxy coating to reduce water loss (first appears with bryophytes).

Alternation of Generations – Core Model

  • Haploid (n) Gametophyte ⇒ makes gametes by mitosis.

  • Fertilization (n + n) → diploid (2n) Sporophyte.

  • Sporophyte undergoes meiosis ⇒ haploid spores in sporangia.

  • Spores germinate ⇒ new gametophytes.

  • Memory aid:
    • Gametophyte → Gametes
    • Sporophyte → Spores

Major Evolutionary Milestones / Lineages

(Use instructor’s whiteboard hierarchy.)

  1. Bryophytes – non-vascular, seedless (mosses, liverworts, hornworts).

  2. Seedless Vascular Plants – first vascular tissue (xylem & phloem).
    • Lycophytes (club mosses) + Pterophytes (true ferns, horsetails).

  3. Gymnosperms – vascular, seeds & pollen but no flowers (“naked seeds”).
    • Pines, spruces, firs, cycads, ginkgo.

  4. Angiosperms – vascular, seeds within fruit, flowers to recruit animal pollinators.
    • Dominate modern flora (~90% of extant plant species).

Vascular Tissue Details (first seen in ferns)

  • Xylem: conducts water & minerals upward from roots; composed of lignified, hollow cells (tracheids, vessels).
    • Instructor promises later discussion of cohesion-tension mechanism.

  • Phloem: conducts sugars (“food”) from photosynthetic sources to sinks; mnemonic from Dr. Shipman: “Phloem = Food.”

  • Lignin: strengthens vascular walls; enables tall growth (woody support).

Lineage-Specific Sections

1. Bryophytes (Mosses, Liverworts, Hornworts)

  • Dominant phase = gametophyte (only group where haploid is what you normally see).

  • Sporophyte = stalk + capsule, nutritionally dependent on gametophyte.

  • Require water for sperm to swim → limited to moist habitats (rainforests, temperate zones w/ heavy rain/snow).

  • Structures:
    • Rhizoids = anchoring filaments, not true roots.
    • Cuticle present but thin.

  • Ecological roles: pioneer species, erosion control, water storage, micro-habitat creation, air-quality bioindicators.

Moss Life Cycle Walk-Through

  1. Mature sporophyte (2n) capsule does meiosis ⇒ haploid spores.

  2. Spores dispersed by wind → land, germinate into protonema → leafy gametophyte.

  3. Gametophyte forms antheridia (♂) & archegonia (♀).

  4. Water film allows sperm to swim to egg ⇒ zygote (2n).

  5. Zygote grows (mitosis) into new sporophyte attached to gametophyte.

2. Seedless Vascular Plants (Ferns & Allies)

  • First appearance of true roots, stems, leaves + vascular tissue.

  • Dominant phase = sporophyte; gametophyte tiny, free-living (< pencil eraser).

  • Still water-dependent for fertilization (flagellated sperm).

  • Lycophytes: club moss, spike moss – produce strobili (cone-like spore clusters).

  • Pterophytes: ferns most “advanced.”
    • Sori = clusters of sporangia on leaf underside.
    • Young sporophyte = “fiddlehead.”

Fern Life Cycle Snapshot

  1. Mature sporophyte leaf underside → sori → sporangia → meiosis → spores (n).

  2. Spore germinates → heart-shaped gametophyte (prothallus) with both antheridia & archegonia.

  3. Sperm swims to egg (water required) ⇒ zygote (2n).

  4. Zygote develops into new sporophyte; gametophyte eventually withers.

Gymnosperms – Brief Preview (foreshadowed)

  • Innovations: pollen (airborne male gametophyte) & seed (embryo + food + waterproof coat).

  • “Gymnosperm” = “naked seed”; no fruit enclosure; cones disperse seeds.

Angiosperms – Brief Preview

  • Added flowers (animal-mediated pollination) + fruit (animal-mediated seed dispersal).

  • Explosion of diversity during mid-Cretaceous (~125{-}150\ \text{Mya}).

  • Example: poison ivy success due to bird-dispersed berries.

Ecological / Practical Significance of Seedless Plants

  • Pioneer colonizers on new substrates (sand bars, barren rock).

  • Create soil, retain moisture, provide insect habitat.

  • Fossil record: ancient tree-sized ferns & lycophytes contributed to coal deposits.

  • Modern uses: decorative (ferns, moss gardens), horticulture (peat), environmental monitoring.

Key Terms to Know (Exam Prep)

  • Alternation of generations, gametophyte, sporophyte, spore, gamete, sporangium, gametangium, antheridium, archegonium.

  • Apical meristem, cuticle, xylem, phloem, lignin.

  • Bryophyte, lycophyte, pterophyte, gymnosperm, angiosperm.

  • Sorus/sori, strobilus/strobili, protonema, prothallus.

  • Invasive vs. native species (examples: Japanese knotweed, hogweed, dandelion).

Numerical / Timeline References

  • Land plants emerge \approx 475\,\text{Mya} (bryophytes).

  • Vascular tissue appears \approx 425\,\text{Mya} (ferns).

  • Gymnosperm innovations \approx 360{-}300\,\text{Mya} (late Devonian–Carboniferous).

  • Angiosperm radiation \approx 150{-}125\,\text{Mya} (mid-Cretaceous).

Concept Connections & Real-World Relevance

  • Plant adaptations (cuticle, vascular tissue, seeds, flowers) mirror environmental challenges (water scarcity, gravity, dispersal).

  • Evolutionary cascade: plant colonization enables terrestrial ecosystems → insects, then vertebrates follow.

  • Modern ecological management: invasive species removal (knotweed battle); monitoring air with mosses; dangers of toxic invasives (hogweed burns).

  • Maple syrup = harvest of phloem sap during spring upward flow.

Ethical / Philosophical Notes

  • Human role in spreading invasives; responsibility for ecological restoration.

  • Mutualisms (flowers–pollinators, fruit–seed dispersers) illustrate co-evolutionary interdependence.

Study Tips / Further Resources

  • Re-watch Bozeman Science (Paul Andersen) videos on “Plant Life Cycles” & “Alternation of Generations” for clarity.

  • Practice drawing moss & fern life cycles; label haploid/diploid stages and processes (meiosis, mitosis, fertilization).

  • Visit a moist woodland or garden: locate moss gametophytes & sporophyte stalks, identify sori on fern leaves.

  • Build flashcards for terminology; quiz yourself on which innovations appear in which lineage.