Transcript A View of Life

Evolution and Diversity of Plants
Chapter 24
Mader: Biology 8th Ed.
Outline
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Evolutionary History
Alternation of Generations
Nonvascular Plants
Vascular Plants
– Seedless
– Seed
– Angiosperms
 Monocots and Eudicots
 Flowers
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Evolutionary History of Plants
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Plants are thought to have evolved from
freshwater algae over 500 mya.
Evolution of plants marked by four
evolutionary events associated with four
major groups of plants.
– Nonvascular Plants
 Advent of nourishment of a multicellular
embryo within the body of the female
plant.
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Evolutionary History of Plants
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Seedless vascular plants
 Advent of vascular tissue.
Gymnosperms and angiosperms
 Produce seeds.
Flowering Plants
 Attract pollinators that give rise to fruits.
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Four Major Plant Groups
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Alternation of Generations
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All plants have a life cycle that includes an
alternation of generations.
– Two multicellular individuals alternate,
each producing the other.
 Sporophyte represents diploid
generation.
 Gametophyte represents haploid
generation.
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Alternation of Generations
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Alternation of Generations
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Alternation of Generations
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Sporophyte (2n) is named for its production
of spores by meiosis.
– Spore is haploid reproductive cell.
Gametophyte (n) is named for its production
of gametes.
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Reduction in Size of Gametophyte
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Alternation of Generations
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Appearance of generations varies widely.
– In ferns, female portions are archegonia
and are fertilized by flagellated sperm.
– In angiosperm, female gametophyte
(embryo sac), consists of an ovule.
 Following fertilization, ovule becomes
seed.
– In seed plants, pollen grains are mature
sperm-bearing male gametophytes.
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Protection of Eggs and Embryos
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Other Terrestrial Adaptations
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Vascular tissue transports water and
nutrients to the body of the plant.
Cuticle provides an effective barrier to water
loss.
Stomata bordered by guard cells that
regulate opening, and thus water loss.
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Leaves of Vascular Plants
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Nonvascular Plants
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Nonvascular plants (bryophytes) lack
specialized means of transporting water and
organic nutrients.
– Do not have true roots, stems, and
leaves.
– Gametophyte is dominant generation.
 Produces eggs in archegonia and
flagellated sperm in antheridia.
 Sperm swim to egg in film of water.
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Nonvascular Plants
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Hornworts (phlym Anthocerophyta) have
small sporophytes that carry on
photosynthesis.
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Nonvascular Plants
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Liverworts (phylum Hepatophyta) have
either flattened thallus or leafy appearance.
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Nonvascular Plants
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Mosses (phylum Bryophyta) usually have a
leafy shoot, although some are secondarily
flattened.
– Can reproduce asexually by
fragmentation.
– Dependent sporophyte consists of foot,
stalk, and sporangium.
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Moss Life Cycle
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Vascular Plants
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Xylem conducts water and dissolved
minerals up from roots.
Phloem conducts sucrose and other organic
compounds throughout the plant.
Lignin strengthens walls of conducting cells
in xylem.
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Vascular Tissue
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Vascular Plants
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Most seedless vascular plants are
homosporous.
– Windblown spores are dispersal agents.
All seed plants are heterosporous and have
male and female gametophytes.
– Seeds disperse offspring.
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Seedless Vascular Plants
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Club Mosses (phylum Lycophyta)
– Typically, branching rhizome sends up
short aerial stems.
– Leaves are microphylls (have only one
strand of vascular tissue).
– Sporangia occur on surfaces of
sporophylls.
 Grouped into club-shaped strobili.
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Club Mosses
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Seedless Vascular Plants
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Ferns and Allies
– Horsetails (phylum Sphenophyta)
 Rhizome produces tall aerial stems.
 Contains whorls of slender, green
branches.
 Small, scalelike leaves also form whorls
at the joints.
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Horsetail
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Ferns
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Whisk Ferns (phylum Psilotophyta)
– Branched rhizome has rhizoids.
– Mutualistic mycorrhizal fungus helps
gather nutrients.
Ferns (phylum Pterophyta)
– Large conspicuous fronds.
 Divided into leaflets.
 Dominant sporophyte produces
windblown spores.
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Whisk Ferns and Ferns
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Fern Life Cycle
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Fern Life Cycle
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Seed Plants
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Seed plants are the most plentiful plants in
the biosphere.
– Seed coat and stored food allow an
embryo to survive harsh conditions during
long period of dormancy.
– Heterosporous
 Drought-resistant pollen grains.
 Ovule develops into seed.
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Gymnosperms
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Gymnosperms have ovules and seeds
exposed on the surface of sporophylls.
– Confiers
– Cycads
– Ginkgoes
– Gnetophytes
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Conifers
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Conifers, as well as other gymnosperm
phyla, bear cones.
– Tough, needlelike leaves of pines
conserve water with a thick cuticle and
recessed stomata.
 Considered a “soft” wood because it
consists primarily of xylem tissue.
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Conifers
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Pine Life Cycle
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Pine Life Cycle
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Cycads
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Cycads (phylum Cycadophyta) have large,
finely divided leaves that grow in clusters at
the top of the stem.
– Pollen and seed cones on separate plants.
 Pollinated by insects.
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Ginkgoes
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Ginkgoes (phylum Ginkgophyta) are
dioecious, with some trees producing seeds
and others producing pollen.
– One surviving species. (Gingko biloba)
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Gnetophytes
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Gnetophytes (phylum Gnetophyta) have
similarly structured xylem, while none have
archegonia, but strobili have similar
construction.
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Angiosperms
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Angiosperms (phylum Anthophyta) are an
exceptionally large and successful group of
plants.
– Ovules are always enclosed within diploid
tissues.
– Became dominant group of plants in the
late Cretaceous and early Paleogene
periods.
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Monocots and Eudicots
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Two classes of flowering plants.
– Monocotyledones (Monocots)
 One cotyledon in seed.
– Eudicotyledones (Dicots)
 Two cotyledons in seed.
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The Flower
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Penducle (flower stalk) expands at tip into a
receptacle.
– Bears sepals, petals, stamens, and
carpels, all attached to receptacle in
whorls.
– Calyx (collection of sepals) protect flower
bud before it opens.
– Corolla (collection of petals).
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The Flower
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Each stamen consists of an anther and a
filament (stalk).
Carpel has three major regions.
 Ovary - Swollen base.
 Fruit
 Style - Elevates stigma.
 Stigma - Sticky receptor of pollen grains.
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Flowering Plant Life Cycle
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Flowering Plant Life Cycle
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Flowers and Diversification
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Wind-pollinated flowers are usually not
showy.
Bird-pollinated flowers are often colorful.
Night-blooming flowers attract nocturnal
mammals or insects.
– Usually white or cream-colored.
Fruits of flowers protect and aid in dispersal.
– Utilize wind, gravity, water, and animals
for dispersal.
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Review
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Evolutionary History
Alternation of Generations
Nonvascular Plants
Vascular Plants
– Seedless
– Seed
– Angiosperms
 Monocots and Eudicots
 Flowers
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.