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Characteristics of Kingdom Plantae
- 1. Multicellular
- 2. Photosynthetic (chloroplasts)
- 3. Cellulose in cell walls
- 4. Starch as a storage polysacharide
- 5. Alternation of generations
- 6. Heterogamy with gametes produced in gametangia
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Nonvascular Plants studied in lab
- Bryophytes:
- Phylum Bryophyta - mosses
- Phylum Hepatophyta - liverworts
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Vascular Plants studied in lab
- Seedless plants:
- Phylum Lycophyta - club mosses
- Phylum Pterophyta - ferns, horsetails, whisk ferns
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Plant Life Cycles
- Alternation of generations: plants alternate between haploid gametophyte generation and a diploid sporophyte generation.
- Diploid sporophyte generation is the dominant generation in all plants except bryophytes.
- Cycle:
- 1. The gametophyte produces gametes inside a jacket of cells forming gametangia.
- 2. Eggs are produced by mitosis in archegonia and sperm are produced in antheridia.
- 3. The gametes fuse by entrance of the sperm into the archegonium, forming a diploid zygote, the first stage of the diploid sporophyte generation.
Plant life cycle produces gametes by mitosis; spores are produced by meiosis.
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Plants less adapted to land
- No vascular tissue (mass).
- No true roots, stems, leaves.
- Sperm swims to egg so water is required for sexual reproduction.
- Gametophyte generation predominates.
- Sporophyte dependent on gametophyte.
- Homospory, one type of spore (all identical).
- Dispersal by spores.
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Plants better adapted to land
- Vascular tissue (xylem, phloem).
- Roots, stem, leaves.
- Water not required for sexual reproduction (sperm nuclei inside pollen grain).
- Sporophyte generation predominates.
- Gametophyte reduced and dependent on sporophyte.
- Heterospory, two kinds of spore (micro [male] and mega [female] spores).
- Dispersal by seeds.
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Spore vs Seed
- Spore:
- A haploid (n) cell inside a dessication resistant coat.
- Germinates to give rise to a multicellular haploid plant-gametophyte.
- Seed:
- A diploid sporophyte embryo plus nutritive material inside a dessication resistant seed coat.
- Germinates to give rise to a multicellular mature diploid plant (sporophyte).
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Nonvascular Plants (Bryophytes)
- Gametophyte is the dominant generation.
- Restricted to moist habitats for their reproductive cycle.
- Remains close to ground enabling the motile sperm to swim from the antheridium to the archegonium and fertilize egg.
- Have a cuticle but lack stomata on the surface of the gametophyte thallus (plant body).
- Stomata is present on the sporophyte in some.
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Bryophyta: Mosses
- Steps of fertilization:
- Sperm swim through a film of water to the archegonium and swim down the neck of the egg.
- The diploid zygote divides by mitosis and develops into an embryonic sporophyte within the archegonium.
- Spores develop by meiosis in the sporangium at the end of the sporophyte. The spores are discharged and in a favolable environment develop into new gametophytes.
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Hepatophyta: liverworts
- Liverworts have a flat thallus.
- Rhizoids; rootlike extensions on the lower surface, that primarily anchor plants.
- Pores; openings that function in gas exchange.
- Gemmae cups; contain flat disks of green tissue called gemmae.
- Gemmae are washed out of the cups when it rains, and they grow into new, genetically identical liverworts.
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Ancestral vs Derived Features of Nonvascular Plants as they relate to Adaptation to Land
- Ancestral:
- Mobile sperm (require water).
- No vascular tissue.
- No roots, stems, leaves.
- Gametophyte dominant.
- Sporophyte depends on gametophyte.
- Derived:
- Cuticle.
- Gameotangia and sporangia.
- Rhizoids.
- Stomata on moss.
- Sporophyte.
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Seedless Vascular Plants
- All have vascular tissue, which is specialized for conducting water, nutrients, and photosynthetic products.
- Sporophyte is the dominant generation.
- Gametophyte usually independent of sporophyte.
- Have well developed leaves, roots, stomata and structural support tissue.
- Retain ancestral feature of motile sperm that require water for fertilization, the gametophyte is small and restricted to moist habitats.
- Lycophyta (club mosses, spike mosses, quillworts) and Pterophyta (ferns, horsetails, whisk ferns).
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Lycophyta: Club mosses
- Usually in moist habitats except Selaginella, the resurrection plant, that inhabits deserts.
- Nonvascular plants and most seedless vascular plants produce one type of spore (homospory).
- Produce two kinds of spores (heterospory), unusual.
- Megaspores; large spores divide by mitosis to produce female gametophyte.
- Microspores; numerous small spores that produce male gametophyte by mitosis.
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Pterophyta: ferns, horsetails and whisk ferns
Psilophytes (whisk ferns) are diminutive, dichotomously branched (Y branches), photosynthetic stems that reproduce sexually by aerial spores.
- Sphenophytes (horsetails) have green jointed stems with occasional clusters of leaves or branches. Their cell walls contain silica that give the stem a rough texture.
- Contain strobili which are clusters of sporangia that produce spores.
- Ferns are the most succesfull occupying deserts to tropical rain forests. They have rhizoids to anchor the plant.
- Contain sori which are clusters of sporangia and leaves called sporophylls.
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Fern Life Cycle
- The haploid spores of ferns fall to the ground and grow into heart-shaped, gametophyte plants.
- All seedless plants depend on an external source of water for a sperm to swim to an egg to effect fertilization and for growth of the resulting sporophyte plant.
- Eggs cells are produced by mitosis in urnlike structures callend archegonia, and sperm cells are produced by mitosis in globular structures callend artheridia.
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Ancestral vs Derived Features of Seedless Vascular Plants as they relate to Adaptation to Land
- Ancestral:
- Sperm requires water for fertilization.
- Reduce gametophyte but usually independent.
- Homospory.
- Derived:
- Vascular Tissue.
- Independent sporophyte.
- Complex stomata.
- Strobili.
- Waxy cuticle.
- Heterospory.
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Features of the Success Land Plants
- Gametangium: protects production of gamtes from drying out.
- Cuticle: prevents dessication of plant body.
- Rhizoid: anchors plant to the ground.
- Motile sperm: liability of land because water is needed for reproduction.
- Vascular tissue: transport and support.
- Gemma cups: production of new haploid plants by asexual reproduction.
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Major difference between the alternation of generations in life cycles
Nonvascular: gametophyte dominate
Seedless: sporophyte dominate
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Structures and Functions
- Antheridium: produce and protect sperm. In gametophyte. Eg. fern, liverwort, mosses.
- Archegonium: produce and protect eggs. In gametophyte. Eg. fern, liverwort, mosses.
- Spore: dispersal. In gametophyte. Eg. fern, liverwort, mosses.
- Gamete: fuse to restore diploid number of chromosomes. In gametophyte. Eg. fern, liverwort, mosses.
- Rhizome: underground stem to anchor the plant. In sporophyte. Only in fern.
- Gemma: asexual reproduction. In gametophyte. Only in liverwort.
- Sporangium: protects spores, site of meiosis. In sporophyte. Eg. moss, fern.
- Strobilus: enhance for dispersal. In sporophyte. Eg. club moss.
- Sorus: enhance for dispersal. In sporophyte. Only in fern.
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