Plant Diversity II: The Evolution of Seed Plants

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Plant Diversity II The Evolution of Seed
Plants

• Campbell, 5th Edition, Chapter 30
• Nancy G. Morris
• Volunteer State Community College

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Evolution of Seed Plants

• Gametophytes of seed plants continue pattern of
  reduction
• Sporophytes continue pattern of dominance
• (Figure 30.1)

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Reproductive Adaptations of Seed Plants

• Gametophyte develops within the spore retained in
  the tissues of the parent sporophyte.
• (Figure 30.1)

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Trend in Dominance of Sporophyte
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Reproductive Adaptations of Seed Plants

• The seed replaced the spore as the main means of
  dispersing offspring. (Figure 30.2)
• The seed, which is the fertilized ovule, consists
  of a sporophyte embryo packaged along with a food
  supply within a seed coat.

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Figure 30.2 From Ovule to Seed
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Reproductive Adaptations of Seed Plants

• Pollen became the vehicles for sperm cells in
  seed plants.
• The pollen grain, which is the immature male
  gametophyte, can be dispersed through the air by
  wind or transported by animals.

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Gymosperms

• Bear their seeds naked on the surfaces of
  sporophylls.
• Pine Life Cycle -- key reproductive adaptation of
  seed plants (Figure 30.4)
• 1) Dominance of the sporophyte
• 2) Development of seed from fertilized ovules
• 3) Flagellated sperm replaced by pollen

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4 Divisions of Gymnosperms

• Division Cycadophyta sago palms
• Division Ginkgophyta ginkgo
• Division Gnetophyta Welwitshia
• Division Coniferophyta pines, firs,
  redwoods, spruce, hemlock, bald cypress
• (Figure 30.3)

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Figure 30.4Gymnosperm Life Cycle
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Angiosperms

• Terrestrial adaptation continued with the
  refinement of vascular tissue
• both xylem vessel elements fibers evolved from
  tracheids, a type of xylem. (Figure 30.5)

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Figure 30.5 Tracheids
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Angiosperms

• The flower is the defining reproductive
  adaptation (Figure 30.6)
• Sepals, petals, stamens (which produce pollen),
  carpels (which produce ovules), are whorls of
  modified leaves that make up flowers.

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Figure 30.6Flower Anatomy
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Angiosperms

• Fruits help disperse the seeds of angiosperms
  (Figure 30.7)
• Ovaries ripen into fruits, which when opened
  disperse seeds to new locations.

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Life Cycle of the Angiosperm

• Alternation of Generations Life Cycle Figure 30.8
• Double fertilization occurs when a pollen tube
  discharges two sperm into the embryo sac (the
  female gametophyte within an ovule). One sperm
  fertilizes the egg, the other combines with two
  nuclei to produce the food-storing endosperm.

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Figure 30.8 Life Cycle of Angiosperm
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Consider this

• Angiosperms animals have shaped one anothers
  evolution.
• Pollination of flowers by animals transport of
  seeds by animals are two important relationships
  in terrestrial ecosystems.
• Agriculture is based almost entirely on
  angiosperms.
• Human cultures depend on the cultivation
  harvest of angiosperms, especially the fruits of
  grains.

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Consider this

• Plants transform the atmosphere and the climate.
• By lowering the concentration of CO2, plants
  probably contribute to the cooling of the Earth.
• Plants are a renewable resource.
• Plant diversity is a nonrenewable resource.
• Destruction of the tropical rainforests is an
  especially urgent problem because they contain
  the greatest diversity of plants on Earth.

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Embryological Development of a Plant