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Plants Chapter 22
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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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The Plant Kingdom Nearly all are multicelled
Vast majority are photoautotrophs Energy from sun Carbon dioxide from air Minerals dissolved in water
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22.1 Evolutionary Trends 295,00 species of plants
Most plants are vascular-internal tissue conducts water and solutes through roots, stems, and leaves 19,000 species are nonvascular-called bryophytes-liverworts, hornworts mosses
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22.1 Evolutionary Trends Seedless vascular plants-wisk ferns, lycophytes, horsetails and ferns Gymnosperms- cycads, ginkgos, gnetophytes and conifers (seed-bearing vascular plants) Angiosperms-Dicots and monocots-two classes of flowering plants
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22.1 Evolutionary Trends Simple roots began to form when plants colonized the land. Later became more specialized roots. Most root systems have many underground absorptive structures with increased surface area.
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22.1 Evolutionary Trends Above grounds shoots evolved-stems, leaves that absorb energy from the sun and carbon dioxide from the air. Plants changed as they began to move into higher and drier places.
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22.1 Evolutionary Trends Diploid zygote forms at fertilization, mitotic cells divide and cell enlargements convert it into a sporophyte. After some of its cells undergo meiosis, haploid resting cells (spores) form.
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22.1 Evolutionary Trends Seed-bearing plants produce two types of spores. This condition is known as heterospory. One type of spore is known as homospory. In gymnospers and angiosperms, macrospores tive rise to female gametophytes in which eggs form and get fertilized.
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22.1 Evolutionary Trends Smaller microspores are the start of pollen grains-cellular structures that become mature, sperm-bearing male gametophytes. Pollen grains travel with the help of wind, birds, insects, and other animals. In drier habitats, seed production also adapted. Female gametophytes of seed-bearing plants form within sporophyte tissue.
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22.1 Evolutionary Trends In most lineages, structural adaption ot life on land included a root system, shoot system, waxy cuticle, stomata, vascular tissues and lignin-reinforced tissue. Lignin- found in cell walls; an organic compound that helps give plant cell its structure.
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Milestones in Plant Evolution
Pg. 343. ? FLOWERING PLANTS CONIFERS CYCADS PROGYMNOSPERMS GINKGOS FERNS HORSETAILS ancestral green algae LYCOPHYTES RHYNIOPHYTES BRYOPHYTES PALEOZOIC MESOZOIC CENOZOIC Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous 505 435 410 360 290 240 205 138 65 Present Time (millions of years ago)
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22.3 Bryophytes- Nonvascular Plants
Fewer than 19,000 species Three groups Liverworts Hornworts Mosses
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Nonvascular Plants Adapted to grow well in fully or seasonally moist habitats. (Mosses are sensitive to pollution, but will grow in almost all other environments-including deserts and Antarctica.)
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Nonvascular Plants Bryophytes Mosses
Thallose liverwort - bilaterally symmetrical rhizoids unicellular radially symmetrical rhizoids multicellular leaves usually with midrib
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Bryophytes Small, nonvascular, nonwooody
Gametophyte dominates life cycle; has leaflike, stemlike, and rootlike parts Usually live in wet habitats Flagellated sperm require water to reach eggs
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Liverworts (simplest)
Types of Bryophytes Liverworts (simplest) Hornworts Mosses (most common)
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Marchantia: A Liverwort
Reproduces asexually by way of gemmae cups Sexual reproduction Gametophytes are male or female Gametes are produced on elevated structures
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Moss Life Cycle Development of mature sporophyte (still attached to gametophyte) Zygote Diploid Stage Fertilization Meiosis Haploid Stage Spores released male gametophyte tip Sperm Male gametophyte female gametophyte tip Female gametophyte Egg
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Peat Mosses 350 species Sphagnum is an example
Grow in acidic bogs; important ecosystems of cold and temperate regions Peat can be harvested and burned as fuel
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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
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Types of Seedless Vascular Plants
Whisk ferns (Psilophyta) Lycophytes (Lycophyta) Horsetails (Sphenophyta) Ferns (Pterophyta) Corksonia
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Ferns (Pterophyta) 12,000 species, mostly tropical
Most common sporophyte structure Perennial underground stem (rhizome) Roots and fronds arise from rhizome Young fronds are coiled “fiddleheads” Mature fronds divided into leaflets Spores form on lower surface of some fronds
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Fern Life Cycle zygote Diploid Stage Haploid Stage
The sporophyte (still attached to the gametophyte) grows, develops. Sori zygote rhizome Diploid Stage fertilization meiosis Haploid Stage Spores are released Spores develop. egg-producing structure egg mature gametophyte (underside) sperm-producing structure sperm Spore germinates gametophyte
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Nonvascular Plants Bryophytes Liverwort
Thallose liverwort - bilaterally symmetrical rhizoids unicellular Liverwort
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Nonvascular Plants Bryophytes are nonvascular plants with flagellated sperm that require liquid water to reach and fertilize the eggs. A sporophyte of these plants develops within gametophyte tissues. It remains attached to the gametophyte and receives some nutritional support from it.
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22.4 Vascular Plants Majority of plants
Have internal tissues that carry water and solutes Two groups Seedless vascular plants Seed-bearing vascular plants
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Seedless Vascular Plants
Arose during the Devonian period Produce spores but no seeds Four main groups Whisk ferns Lycophytes Horsetails Ferns
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Seedless Vascular Plants
Most seedless vascular plants live in wet, humid places. Their gametophytes lace vascular tissues. Water clinging to these plants are the only means for flagellated sperm to reach the eggs.
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Geologic Time Table http://www.plantapalm.com/
vce/evolution/timetable.htm
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Evolutionary Trend zygote SPOROPHYTE (2n) GAMETOPHYTE (n) GREEN ALGA
BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM
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Seedless Vascular Plants
Psilotum grows wild in Florida woodlands and all members of the division, Psilophyta, today are tropical plants
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Seedless Vascular Plants
Psilotum grows wild in Florida woodlands and all members of the division, Psilophyta, today are tropical plants
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Seedless Vascular Plants
Running pine or Lycopodium complanatum, an Ohio native
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Seedless Vascular Plants
Equisetum palustre Strobili Horsetails
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Seedless Vascular Plants
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22.5 Seed-Bearing Vascular Plants
Gymnosperms arose first Cycads Ginkgos Gnetophytes Conifers Angiosperms arose later Monocots Dicots
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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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Conifer 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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Cycads Most diverse during age of dinosaurs Only 100 living species
Two species of Zamia are native to U.S. Palmlike appearance Pollen-bearing and seed-bearing cones on different plants
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Ginkgos Diverse during age of dinosaurs
Only surviving species, Ginkgo biloba, is native to China Deciduous tree with fan-shaped leaves Trees are male or female Female trees produce seeds covered with a fleshy, foul-smelling coat
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3 Genera of Gnetophytes Gnetum - Tropical climbing vines
Ephedra (joint fir, Mormon tea) Welwitschia mirabilis
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Pine Cones Woody scales of a “pine cone” are the parts of where megaspores formed and developed into female gametophytes Male cones, where microspores and pollen are produced, are not woody
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Pine Life Cycle Female cone Sporophyte ovule Male cone Pollen sac Seed
fertilization meiosis egg View inside ovule microspores megaspores Pollen tube
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Conifer Distribution Conifers dominated during Mesozoic
Reproduce more slowly than angiosperms; at competitive disadvantage in many habitats Still dominate in far North, at higher elevations, and in certain parts of Southern Hemisphere
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Rise of Seed-Bearing Plants
Seeds appeared about 360 million years ago Seed ferns and gymnosperms were dominant at first Angiosperms arose later
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Special Traits of Seed-Bearing Plants
Pollen grains Arise from megaspores Develop into male gametophytes Can be transported without water Seeds Embryo sporophyte inside nutritive tissues and a protective coat Can withstand hostile conditions
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Vascular Plants
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Adaptations to Land Root systems Shoot systems Vascular tissues
Waxy cuticle for water conservation
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Seed-Bearing Vascular Plants
Conifers Giant redwoods- the tallest trees Bristle-coned pines The oldest trees
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Angiosperms Flowering plants Dominant land plants (260,000 species)
Defining feature: Ovules and (after fertilization) seeds are enclosed in an ovary Two classes: Monocots and dicots
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Structure of Flower and Seed
endosperm embryo ovule ovary seed coat
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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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Seed-Bearing Plants Microspores that give rise to pollen grains
Megaspores inside ovules More water-conserving than seedless vascular plants
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Pollen Pollen grains are sperm-bearing male gametophytes that develop from microspores Allows transfer of sperm to egg without water Can drift on air currents, or be carried by pollinators
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Ovules 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
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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 that supports embryo
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People and Plants Plant domestication began about 11,000 years ago
About 3,000 species have been used as food Now about 200 plants are major crops
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Nonfood Uses of Plants Lumber, paper, and fuel from conifers
Furniture from hardwoods Rope from agave, hemp Thatched roofing from grasses, palms Natural insecticides Drugs from foxglove, periwinkle
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Plants of Abuse Tobacco plants are Nicotiana sp.
Cannabis sativa is source of marijuana Coca leaves are used to produce cocaine Toxic plant alkaloids, such as henbane and belladona, have been used as poisons and as medicine
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Review Chart pg. 354 Summary and Review Questions, Self Quiz and end of chapter readings.
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