Chapter 22

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Chapter 22 Plants with Seeds

• Courtesy of Mr. B.

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GYMNOSPERMS Non-Flowering Seed Producers
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Transition from Ferns to Land PlantsMedullosa
the seed fern
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• Gymnosperms began to dominate landscapes as
  climates became drier at the end of the Paleozoic
  era 245 mya
• Gymnosperms appear in the fossil record much
  earlier than flowering plants, and they
• Lack enclosed chambers in which seeds develop.
• Are grouped into four divisions
• Cycadophyta, Ginkgophyta, Gnetophyta and
• Coniferophyta.

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GYMNOSPERMS Plants with seeds that are not
enclosed within a fruit, derive their name from
the Greek words gymnos (naked) and sperma (seed).
In this plant group, the seeds are produced on
the open surface of a scale. Unlike flowering
plants, the gymnosperms do not form true flowers
or fruits. There are four divisions of
gymnosperms. Examples of gymnosperms include
cycads, ginkgo, conifers and gnetops.
Kingdom  Plantae - Plants
Subkingdom  Tracheobionta -- Vascular plants
Superdivision  Spermatophyta - Seed plants
Division  Cycadophyta - Cycads
Class  Cycadopsida
Order  Cycadales
Family  Cycadaceae
Genus Cycas- cycads
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• Evolutionary advancements of Gymnosperms over the
  ferns and allies
• Seeds
• Lack of dependence on water for fertilization
  (air-borne pollen)
• Progressively more dominant sporophyte
• Life Cycle
• In the gymnosperms and the flowering plants, the
  sporophyte generation is dominant with the
  gametophyte contained in and dependent on the
  sporophyte.
• Vascular System
• They do have a well-developed vascular system of
  xylem and phloem and have true roots, stems, and
  leaves.
• The vascular tissues are significantly more
  efficient and effective than the vascular systems
  of the seedless plants such as the ferns.
• Gymnosperms are usually woody plants. The xylem
  form the wood if a tree and the phloem tissues
  are part of the bark (along with cork). The
  formation of wood from secondary growth is the
  reason that some sporophytes can reach such large
  sizes.

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The Gymnosperms
The Cycad a fernlike gymnosperm. Note the cone,
or strobilus
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Male cones of Pinus nigra

• Unlike the seedless vascular plants, conifers are
  more prevalent in cooler regions and in desert
  habitats.
• leaf curled to reduce water loss
• evolved cold hardiness

Female cones of Pinus nigra
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The Gymnosperms
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More Gnetophytes!
All bear cones, with naked seeds, which is an
adaptation over the ferns, that produced spores
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Ginkgophyta Ginkgo biloba The link between
gymnosperms and angiosperms (note the fleshy
seed)
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Monocot vs. Dicot Seeds
Corn
Bean
Seed coat
Stored food(Endosperm)
Embryoplant
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Monocot Seeds

• Monocot seeds have
• Endosperm
• One cotyledon

seed coat
endosperm
cotyledon
coleoptile
radicle
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Dicot Seeds

• Dicot seeds have
• No endosperm at maturity
• Two cotyledons

Seed coat
First leaves
Early root
Cotyledon
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Organization of primary tissues in a young dicot
stem (eg. Bean)
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The primary tissues of a young monocot stem (eg.
Corn)
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Primary tissues of a young dicot root
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Cross-section through a monocot root
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Development of Seeds

• Function of seed structures
• Endosperm Nutrition for embryo
• Endosperm Cotyledon(s)
• Cotyledons Nutrition for embryo

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Overall, what is the function of a seed?

• Protects young embryo
• Provides nutrition for the developing embryo
• Allows dispersal of the embryo over time space

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Seed to Seedling
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Angiosperms

• Replaced Gymnosperms as the dominant plant type
  during the Cretaceous Period 60 million years ago
• Produce flowers, fruits, and seeds

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Flower Morphology
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General Angiosperm Life Cycle
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Pollination

• Pollination can occur through biotic and abiotic
  means (wind, water, birds, insects, etc)
• Morphological characteristics of flowers attract
  specific pollinators

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Insects the Great Pollinators
Conventional spectrum
What bees see ?
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Bats as Pollinators
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Fruits

• Fruit. Mature ovary of the a flower that
  protects dormant seeds and aids their dispersal
• Seeds are the product of pollination
• Seeds are located within fruits
• There are many different types of fruits

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Fruit Types
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Seed Dispersal

• Seeds are highly adapted to dispersal
• Examples of morphological characteristics would
  be buoyancy in fruits (coconut) and wings
  (maple seeds)

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While others are simply blowing in the wind.
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Some seeds are dispersed as a result of being
eaten and mingling with feces.