Lecture 9 Outline (Ch. 38)

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Lecture 9 Outline (Ch. 38)

• I. Flower Structures
• II. Life cycle
• III. Gametophyte production Dispersal
• Pollination
• Fertilization
• Germination
• VII. Lecture Concepts

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Angiosperm Overview
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Angiosperm Overview

• In alternation of generations in angiosperms, the
  dominant stage is the diploid
• sporophyte
• Spores develop inside the flower into tiny,
  haploid gametophytes
• the male pollen grain and the female embryo sac
  (Figure 38.3)

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Angiosperm Lifecycle
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Angiosperm Gametophytes

• Develop with anthers and ovaries, respectively
• Pollen develops from microspores inside the
  sporangia of the anther
• Within an ovule, a haploid megaspore divides by
  mitosis and forms the embryo sac, the female
  gametophyte

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Angiosperm Gametophytes
Figure 38.3
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Angiosperm Pollination

• brings female and male gametophytes together
• Fertilization (syngamy) is preceded by
  pollination, the placing of pollen on the stigma
  of the carpel

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Abiotic Pollination by Wind
Hazel staminate flowers (stamens only)
Hazel carpellate flower (carpels only)
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Pollination by Bees
Common dandelion under normal light
Common dandelion under ultraviolet light
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Pollination by Moths and Butterflies
Anther
Stigma
Moth on yucca flower
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Pollination by Flies
Fly egg
Blowfly on carrion flower
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Pollination by Birds
Hummingbird drinking nectar of poro flower
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Pollination by Bats
Long-nosed bat feeding on cactus flower at night
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Angiosperm Pollination

• The pollen grain produces a pollen tube that
  extends down the style toward the embryo sac
• Two sperm are released and effect a double
  fertilization, resulting in a diploid zygote and
  a triploid (3n) endosperm (Figure 38.5)

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Angiosperm Fertilization
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Angiosperm Seed Formation

• develops into a seed containing a sporophyte
  embryo and a supply of nutrients (Figure 38.7)
• The zygote gives rise to an embryo with apical
  meristems and one or two cotyledons
• Mitosis of the triploid (3n) endosperm gives rise
  to a multicellular, nutrient-rich mass that feeds
  the developing embryo and later (in some plants)
  the young seedling

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Angiosperm Seed Formation
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The Ovary ...

• develops into a fruit adapted for seed dispersal
• a fruit is a mature ovary that protects the
  enclosed seeds and aids in their dispersal via
  wind, water, or animals

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Dispersal by Water
Coconut
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Dispersal by Wind
Winged seed of Asian climbing gourd
Dandelion parachute
Winged fruit of maple
Tumbleweed
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The Mature Seed

• The embryo and its food supply are enclosed by a
  hard, protective seed coat
• The seed enters a state of dormancy
• In some eudicots, such as the common garden bean,
  the embryo consists of the embryonic axis
  attached to two thick cotyledons (seed leaves)
• A monocot embryo has one cotyledon

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Angiosperm Seeds
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Evolutionary Adaptations ...

• the process of germination increases the
  probability that seedlings will survive
• Germination begins when seeds imbibe water
• this expands the seed, rupturing its coat, and
  triggers metabolic changes that cause the embryo
  to resume growth
• The embryonic root, or radicle, is the first
  structure to emerge from the germinating seed
• Next, the embryonic shoot breaks through the soil
  surface (Figure 38.9)

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Seed Germination (bean)
(a) Common garden bean
Foliage leaves
Cotyledon
Epicotyl
Hypocotyl

Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
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Many Plants Can ...

• clone themselves by asexual reproduction
• Asexual reproduction (cloning) is the
  reproduction of genetically identical offspring
  from a single parent
• Apomixis
• production of seeds without fertilization

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Vegetative Reproduction Agriculture

• Humans have devised various methods for asexual
  propagation of angiosperms
• Cuttings can be taken from many kinds of plants
• They are asexually reproduced from plant
  fragments
• Grafting is a modification of vegetative
  reproduction from cuttings
• A twig or bud from one plant can be grafted onto
  a plant of a closely related species or a
  different variety of the same species

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Vegetative Reproduction Agriculture

• Maize
• Is a product of artificial selection by humans
• Is a staple in many developing countries, but is
  a poor source of protein

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Self-Check
Part of plant Function Later becomes Examples
Ovary Contains eggs (ovules) Flesh of fruit Apples, strawberries, coconut meat
Pollen
Ovule
Integuments
Cotyledons
Endosperm
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Lecture 9 concepts

• Describe the parts of a flower. Define
  angiosperms.
• Explain the process that plants use for
  generating pollen and eggs/ovules.
• Contrast pollination and fertilization.
• Discuss several types of pollination
  methods/pollinators.
• Diagram/explain what each part of the fertilized
  ovule, coverings, and ovary becomes.
• What is the purpose of a fruit? Describe
  methods of seed dispersal.
• Compare monocot and dicot seeds.
• List the steps of germination. How do seeds know
  when to germinate?
• How have humans changed the way plants develop?
  (many answers)
• Write out a list of new terminology and provide
  descriptions