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Plant Evolution Chapter 26
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Beginnings and Endings
Impacts, Issues Video Beginnings and Endings
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Setting the Stage for Plants
Earth’s atmosphere was originally oxygen free Ultraviolet radiation bombarded the surface Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer
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Invading the Land Cyanobacteria were probably the first to spread into and up freshwater streams Later, green algae and fungi made the journey together Every plant is descended from species of green algae
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Evolutionary Tree for Plants
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The Plant Kingdom Nearly all are multicellular Eukaryotic Terrestrial
Vast majority are photoautotrophs Energy from sun Carbon dioxide from air Minerals dissolved in water
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Plant Kingdom Adaptations to land Well developed tissue Cuticle
Stomata Protection of embryo Alternations of generations Sporophyte Diploid Produces spores by meiosis Reproductive structure Develops into new organism without the need to fuse with another reproductive cell
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Plant Kingdom Gametophyte Haploid Produces gametes Egg and sperm
Formed by mitosis Egg and sperm fuse to form zygote Undergoes mitosis Forms sporophyte
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Evolutionary Trend multicelled sporophyte (2n) mitosis zygote (2n)
Diploid Haploid fertilization meiosis gametes (2n) spores (2n) multicelled gametophytes (n) mitosis mitosis
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Haploid to diploid dominance
Evolutionary Trend Haploid to diploid dominance
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zygote only, no sporophyte
sporophyte’s importance gametophyte’s importance green algae bryophytes ferns gymnosperms angiosperms
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4 Major Groups of Plants Nonvascular (Bryophytes) Seedless Vascular
Gymnosperms Angiosperms
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Nonvascular Plants 3 types of plants Hornworts
Symbiotic relationship with cyanobacteria Liverworts Mosses Peat, true and rock Sphagnum Great ability to absorb water
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Peat Mosses
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Marchantia: A Liverwort
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Marchantia: A Liverwort
Female gametophyte Male gametophyte
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Nonvascular Plants Lack specialized means of transporting water, nutrients Do not have true roots, stems or leaves Have root, stem and leaf like structures Rhizoids Threadlike cellular structures Absorb water and nutrients Anchor gametophytes to substrates
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Nonvascular Plants Gametophyte Dominant generation Archegonia
Produces and protects eggs Antheridia Produce flagellated sperm Sperm swims to egg and forms embryo - develops into sporophyte - sporophyte derives nutrition from gametophye - produces spores
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Seedless Vascular Plants
Like bryophytes Live in wet, humid places Require water for fertilization Unlike bryophytes Sporophyte is free-living and has vascular tissues Epiphytes Plants live on trees but are not parasitic
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Seedless Vascular Plants
Vascular tissue Microphylls 1 strand of vascular tissue Club mosses, horse tails, whisk ferns Macrophylls Many strands of vascular tissue Ferns
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Seedless Vascular Plants
Xylem Conducts water and dissolved nutrients upwards from the roots Contain lignin Stronger for support and waterproof Protects from parasites and predators Phloem Conducts sucrose and other organic compounds throughout the plant
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Seedless Vascular Plants
Reproduction Moist environment Homosporous Large sporophyte with vascular tissue Gametophyte small and independent
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Seed-Bearing Vascular Plants
Pollen grains Arise from microspores Develop into male gametophytes Can be transported without water Seeds Embryo sporophyte inside nutritive tissues and a protective coat Can withstand hostile conditions More water-conserving
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Pollen pine pollen grains
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Seed-Bearing Vascular Plants
Female reproductive structures that become seeds Consist of: Female gametophyte with egg cell Nutrient-rich tissue Jacket of cell layers that will form seed coat Pollination Can occur by wind or by pollinators No external water is needed for fertilization
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Ovules
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Gymnosperms Plants with “naked seeds” Seeds don’t form inside an ovary
Four groups Conifers Ginkgos Cycads Gnetophytes
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Gymnosperm Characteristics
Widest known, largest number of living species Woody trees or shrubs Most are evergreen Bear seeds on exposed cone scales Most produce woody cones
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Gymnosperms Conifers Evergreens, pines, firs Needle like leaves
Conserve water Thick cuticle Recesses stomata Monoeicious Tree produces both male and female gametophytes Pollinated by wind
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Gymnosperms Ginkgo bilboa Dioecius Resistant to pollution
Pollen tube bursts to release multiflagellated sperm Female trees gives off fowl odor when seeds ripen
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Strobilus of a “female” cycad
Gymnosperms Cycads Dioecius Pollinated by insects Palmlike appearance Strobilus of a “female” cycad
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Gymnosperms Gnetophytes Don’t have archegonia
Most closely related to angiosperms Produce nectar Sporophyte of Ephedra
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Angiosperms Flowering plants Dominant land plants
Ovules and (after fertilization) seeds are enclosed in an ovary Three main groups Magnoliids Monocots Eudicots
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Angiosperms Eudicots Monocots 2 seed coats 1 seed coat
Flower parts in 4’s or 5’s Woody or herbaceous Net veins Vascular bundles in ring taproot Monocots 1 seed coat Flower parts in 3’s or multiples of Herbaceous Parallel veins Scattered bundles in stem Fibrous roots
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Inside seeds, two cotyledons seed leaves of embryo
Inside seeds, one cotyledon seed leaf of embryo Usually four or five floral parts (or multiples of four or five) Usually three floral parts (or multiples of threes) Leaf veins usually in a netlike array Leaf veins usually running parallel with one another Three pores or furrows in the pollen grain surface One pre or furrow in the pollen grain surface Vascular bundles organized as a ring in ground tissue Vascular bundles distributed throughout ground tissue
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Angiosperms 4 main parts Sepals (calyx) Protect flower bud
Usually green Petals (corolla) Vary in shape, size and color Stamen 2 parts filament anther sac-like container pollen grains develop
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Angiosperms Carpel 3 regions Stigma Enlarged sticky knob Style
Slender stalk Ovary Enlarged base encloses 1 or more ovule Ovule becomes seed Ovary becomes fruit
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petal stamen (microspores form here) sepal carpel (megaspores form here) ovule in an ovary
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Angiosperms Complete flower Contains all 4 parts Incomplete flower
Missing 1 of the 4 parts Perfect flower Has both stamen and carpel Imperfect flower Has either the stamen or carpel
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Double Fertilization Distinctive feature of angiosperms
Male gametocyte delivers two sperm to an ovule One fertilizes egg; other fertilizes a cell that gives rise to endosperm
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Flowering Plant Life Cycle
sporophyte Flowering Plant Life Cycle Diploid Double fertilization Meiosis Meiosis Haploid mitosis without cytoplasmic division microspores pollination two sperm enter ovule female gametophyte
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