IX. Leaf abscission (leaf drop)

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IX. Reproductive Structures of Flowering Plants

• A. Sporophyte
• 1. Growth
• Mitotic division of a fertilized egg
• 2. Flowers
• Gametophytes
• Sperm
• Eggs

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Carpel
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X.
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A. A New Generation Begins

• 1. Cells in pollen sacs undergo meiosis to form
  microspores
• 2. Mitosis forms male gametophyte (pollen grains)

• 3. Cells in ovule undergo meiosis to form
  megaspores
• 4. Mitosis without cytoplasmic division forms
  female gametophyte

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B. Pollination to Fertilization

• 1. Pollination
• Pollen grains to stigma
• 2. Pollen tube grows to and penetrates embryo
  sac, releases two sperm
• 3. Double fertilization
• One sperm fuses with egg nucleus (2n)
• One sperm fuses with nuclei of endosperm mother
  cell (3n)

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C. How do plants get pollen from one plant to
another? (plants are rooted in the ground)
A. Wind 1. Gymnosperms and some flowering
plants (grasses many trees)2. Hit or miss
affair (very chancy) B. Many flowering plants
rely on animals for cross-pollination 1. 3 main
animal pollinators- insects, birds, and mammals
a. Insect pollinators- beetles, bees, wasps,
flies, butterflies, and mothsb. Bird
pollinators- hummingbirds, honey creepers, and
honeyeatersc. Mammals- bats 2. Many plants have
evolved relationships with animals that are their
pollinators (co-evolution)
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• D. Seed Structure (a mature ovule)
• 1. Seed coat
• 2. Radicle embryonic root
• 3. Plumule embryonic leaves
• 4. Epicotyl and hypocotyl shoot
• 5. Cotyledons (seed leaves) derived from
  endosperm

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• E. Fruit a mature ovary which usually contains
  a seed

See Table on pg 537
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F. Seed Dispersal

• Wind Dispersal Maple Tree, Dandelion
• - goal is to land far enough away so they do not
  have to compete with parent plants
• Animals
• seed adheres to animal w/ hooks, hairs, and
  sticky surfaces
• Seed survives digestion due to thick seed coat
• Water Dispersal
• Waxy coat to avoid water penetration (coconut
  fruit)
• Sacs of air to help them float
• Humans imports and exotic species
• Explosives - Impatiens

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1. Asexual Reproduction in Plants (See Table pg 540)

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XII. Growth and Development Overview (Chp 32
pgs 546-547)
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XIII. Plant hormones

• A. Definition an organic compounds produced in
  one part of a plant, transported to another
  part, where it stimulates a physiological
  response
• B. Five major types
• 1. Auxins a. Stimulates cell
  elongation in the stem and thereby
  phototropism of the plant
• b. Produces apical dominance by inhibiting
  lateral bud growth
• c. Transported through parenchyma

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• 2. Cytokinins
• a. Produced in roots
• b. Stimulate lateral buds
• c. Delay plant aging
• 3. Ethylene (a gas)
• a. Triggers ripening in fruits
• b. Produced in nodes, fruit, and aging tissue
• 4. Gibberellins
• a. Promote stem elongation
• b. Promote seed germination
• 5. Abscisic acid
• a. Closes stomata under water stress
• b. Delays germination of seeds in cold (high
  levels in seeds)

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XIV. Rate and Direction of Growth

1. Gravitropism growth response to Earths gravity
2. Phototropism leaves adjust rate and direction
   of growth in response to light
3. Thigmotropism plant shifts direction of growth
   when in contact with solid object

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XV. Photoperiodism

• A. Processes by which plants control their
  cycles using periods of lightness and darkness
• B. Types of plants affected by photoperiods
• 1. Long-day plants - plants affected by a
  critical period of darkness or less
• a. Flower in spring and early summer
• b. Clover, black-eyed Susan, spinach (14 hrs.)
• 2. Short-day plants - plants affected by a
  critical period of darkness or more
• a. Flower in late summer or fall
• b. Chrysanthemum, poinsettia

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• C. Phytochromes - light-absorbing pigments that
  affect a plants photoperiod
• 1. In short-day plants Pfr inhibits flowering.
  A long night means more Pr and therefore lower
  Pfr levels. Result is flowering
• 2. In long day plants Pfr induces flowering.
  A short night means more Pfr. Result is flowering

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XVI. Leaf abscission (leaf drop)

• A. Purpose - to prevent plant dehydration due to
  transpiration when ground water is locked up in a
  frozen state
• B. Process
• 1. In the fall woody parts of plant reabsorb
  valuable minerals from the leaves
• 2. Chlorophyll breaks down leaving and
  revealing accessory pigments (carotenoids
  and xanthophylls)
• 3. Changes occur in abscission zone, which has
  few fibers and is mostly parenchyma
• a. Protective layer of cork cells forms
• b. Enzymes digest cell walls in the zone
• c. With connection weakened some
  mechanical force (wind) knocks leaf off tree

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Petiole
Twig
Abscission zone