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Plant Diversity II

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Plant Diversity II Level 1 Biological Diversity Jim Provan Campbell: Chapter 30 Reproductive adaptations of seed plants Three life cycle modifications led to the ... – PowerPoint PPT presentation

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Title: Plant Diversity II


1
Plant Diversity II
  • Level 1 Biological Diversity
  • Jim Provan

Campbell Chapter 30
2
Reproductive adaptations of seed plants
  • Three life cycle modifications led to the success
    of terrestrial plants
  • Reduction of the gametophyte retained in the
    moist reproductive tissue of the sporphyte
  • Origin of the seed
  • Zygotes developed into embryos packaged with a
    food supply within a protected seed coat
  • Seeds replaced spores as the main means of
    dispersal
  • Evolution of pollen plants were no longer tied
    to water for fertilisation

3
Reduction of gametophytes in seed plants
4
In seed plants, the seed replaced the spore as
the main means of dispersing offspring
  • Relatively harsh terrestrial environment
  • Bryophytes and seedless vascular plants release
    spores
  • Seeds are more hardy because of their
    multicellular nature
  • Seed is a sporophyte embryo and a food supply
    surrounded by a protective coat
  • All seed plants are heterosporous
  • Development of seed associated with
    megasporangia
  • Seed plant megasporangia are fleshy structure
    called nucelli
  • Additional tissues (integuments) surround
    megasporangium
  • Resulting structure is called an ovule
  • Female gametophyte develops in wall of megaspore,
    is fertilised (embryo) and resulting ovule
    develops into a seed

5
From ovule to seed
6
Pollen became the vehicle for sperm cells in seed
plants
  • Microspores develop into pollen grains which
    mature to form the male gametophytes of seed
    plants
  • Pollen grains coated with a resistant polymer,
    sporopollenin
  • Can be carried away by wind or animals (e.g.
    bees) following release from microsporangia
  • A pollen grain near an ovule will extend a tube
    and discharge sperm cells into the female
    gametophyte within the ovule
  • In some gymnosperms, sperm are flagellated
    (ancestral)
  • Other gymnosperms (including conifers) and
    angiosperms do not have flagellated sperm cells

7
Gymnosperms
  • Descended from Devonian progymnosperms
  • Seedless
  • Seeds evolved late Devonian
  • Climatic changes during Permian led to lycopods,
    horsetails and ferns being replaced by conifers
    and cycads
  • Lack enclosed chambers (ovaries) in which seeds
    develop

8
Four divisions of extant gymnosperms
9
Conifers are the largest division of gymnosperms
  • Mostly evergreens e.g. pines, firs, spruces,
    larches, yews, cypresses etc.
  • Include the tallest, largest and oldest living
    organisms
  • Needle-shaped leaves adapted to dry conditions
  • Thick cuticle covers leaf
  • Stomata in pits, reducing water loss
  • Megaphylls cf. other leaves

10
The life cycle of a pine
11
Angiosperms
12
Angiosperms (flowering plants)
  • Flowering plants are the most widespread and
    diverse (250,000 species)
  • Only one division (Anthophyta), with two classes
  • Monocotyledons
  • Dicotyledons
  • Less dependent on wind pollination - use insects
    and animals

13
Evolution of vascular tissue in angiosperms
  • Conifers have water-conducting cells called
    tracheids
  • Angiosperms have vessel elements
  • More specialised for transport
  • Less specialised for support
  • Xylem reinforced by fibres
  • Specialised for support - thick lignified wall
  • Evolved in conifers (conifers lack vessel
    elements)

14
The flower is the defining reproductive
adaptation of angiosperms
  • Sepals sterile, enclose bud
  • Petals sterile, attract pollinators
  • Stamen produces pollen
  • Carpel evolved from seed-bearing leaf that
    became rolled into a tube
  • Stigma sticky structure that receives pollen
  • Ovary protects ovules, which develop into seeds
    after fertilisation

15
Fruits help disperse the seeds of angiosperms
  • Fruits are ripened ovaries that protect dormant
    seed and aids in its dispersal
  • Modifications of fruits that aid dispersal
    include
  • Seeds within fruits that are shaped like kites or
    propellors (e.g. maple)
  • Burr-like fruit that cling to animal fur
  • Edible fruit - tough seeds pass through digestive
    tract

16
Life cycle of an angiosperm
17
Angiosperms and animals shaped one anothers
evolution
  • Coevolution reciprocal evolutionary responses
    among two or more interacting species
  • Coevolution led to diversity of flowers
  • Flower-specific pollinators
  • Usually adapted for types of pollinators
  • Attraction of ripening fruits
  • Soft, fragrant and sugary
  • Attractive change of colour

18
Plants transformed the atmosphere and the climate
  • Plants decreased atmospheric carbon dioxide,
    resulting in global cooling
  • Cooler environment made terrestrial life more
    habitable for other organisms
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