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IX. Reproductive Structures of Flowering Plants

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

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ix reproductive structures of flowering plants
IX. Reproductive Structures of Flowering Plants

A. Sporophyte

1. Growth

  • Mitotic division of a fertilized egg

2. Flowers

  • Gametophytes
    • Sperm
    • Eggs
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

A. A New Generation Begins
b pollination to fertilization
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)
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)
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

See Table on pg 537

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

f seed dispersal
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
xiii plant hormones
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

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)

xiv rate and direction of growth
XIV. Rate and Direction of Growth
  • Gravitropism – growth response to Earth’s gravity
  • Phototropism – leaves adjust rate and direction of growth in response to light
  • Thigmotropism – plant shifts direction of growth when in contact with solid object
xv photoperiodism
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

C. Phytochromes - light-absorbing pigments that affect a plant’s 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

xvi leaf abscission leaf drop
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



Abscission zone