Photosynthesis

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Outline

• Evolutionary History
• Alternation of Generations
• Nonvascular Plants
• Vascular Plants
• Seedless
• Seed
• Angiosperms
• Monocots and Eudicots
• Flowers

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Evolutionary History of Plants

• More than 98 of all biomass is plants
• Multicellular photosynthetic eukaryotes
• 280,000 known species
• 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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Representatives of theFour Major Groups of Plants
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Evolutionary History of Plants

• 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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Evolutionary History of Plants
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Alternation of Generations

• Life cycle involves alternation of generations
• Multicellular 1n individuals (gametophytes)
  produce multicellular 2n individuals
  (sporophytes)
• Multicellular 2n individuals (sporophytes)
  produce multicellular 1n individuals
  (gametophytes)
• Sporophyte (2n)
• Multicellular individual that produces spores by
  meiosis
• Spore is haploid cell that will become the
  gametophyte
• Gametophyte (1n)
• Multicellular individual that produces gametes
• Gametes fuse in fertilization to form zygote
• Zygote is a diploid cell that will become the
  sporophyte

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Alternation of Generations
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Alternation of Generations

• 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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Reduction in the Size of the Gametophyte
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Other Terrestrial Adaptations

• 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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Protection of Eggs and Embryos
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Leaves of Vascular Plants
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Nonvascular Plants

• 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
• Produces flagellated sperm in antheridia
• Sperm swim to egg in film of water to make zygote

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Nonvascular Plants

• Hornworts (phlym Anthocerophyta) have small
  sporophytes that carry on photosynthesis
• Liverworts (phylum Hepatophyta) have either
  flattened thallus or leafy appearance
• 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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Hornwort
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Liverwort, Marchantia
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Moss (Polytrichum) Life Cycle
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Vascular Plants

• 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
• 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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Cooksonian Fossil
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Vascular Tissue
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Seedless Vascular Plants

• 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 Moss, Lycopodium
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Seedless Vascular Plants

• 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, Equisetum
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Ferns

• 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 fern, Psilotum
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Diversity of ferns
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Fern Life Cycle
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Seed Plants

• 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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Seed Plants
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Gymnosperms

• Gymnosperms have ovules and seeds exposed on the
  surface of sporophylls
• Confiers
• Cycads
• Ginkgoes
• Gnetophytes

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Conifers

• 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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Pine Life Cycle
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Cycads

• Cycads (phylum Cycadophyta)
• 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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Cycad Cones
Figure 24.19
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Ginkgoes

• Ginkgoes (phylum Ginkgophyta)
• Dioecious
• Some trees producing seeds
• Others producing pollen
• One surviving species (Gingko biloba)

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The Ginkgo Tree
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Ephedra
Figure 24.21
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Welwitschia miribilis
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Gnetophytes

• Gnetophytes (phylum Gnetophyta)
• Have similarly structured xylem
• None have archegonia
• Strobili have similar construction

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Angiosperms

• Angiosperms (phylum Anthophyta)
• 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 Paleocene periods

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Amborella trichopoda
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Monocots and Eudicots

• Two classes of flowering plants
• Monocotyledones (Monocots)
• One cotyledon in seed
• Eudicotyledones (Dicots)
• Two cotyledons in seed

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Flower Diversity
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The Flower

• Peduncle (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

• 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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Generalized Flower
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Flowering plant life cycle
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Flowers and Diversification

• 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

• Evolutionary History
• Alternation of Generations
• Nonvascular Plants
• Vascular Plants
• Seedless
• Seed
• Angiosperms
• Monocots and Eudicots
• Flowers

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