Topic 13 Introduction to the Kingdom Plantae

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Topic 13Introduction to the Kingdom Plantae

• Biology 1001

November 2, 2005
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LAND Plants The Tree of Life
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13.1 What Are Plants?

• Plants colonized land approximately 500 MYA
• Land plants are a monophyletic group!
• Land plants evolved from aquatic green algae
• 290,000 living species
• Producers sources of O2 and food for land
  animals

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General Features of Land Plants

• Multicellular, eukaryotic photoautotrophs
• Cell walls containing cellulose
• Chloroplasts containing chlorophylls a and b
• What Features DEFINE plants?
• The Evolution of Land Plants
• Features shared with charophyceans
• Terrestrial adaptations that characterize land
  plants
• Origin and diversification of land plants

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Land Plants Evolved From Green Algae

• Green algae called charophyceans are the closest
  living relatives of land plants
• Evidence
• Rosette cellulose-synthesizing complexes
• Peroxisome enzymes that minimize photorespiration
• Similarity of sperm structure
• Formation of a phragmoplast
• Similar nuclear and chloroplast genomes
• Adaptation to a dry environment sporopollenin

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Adaptations to a Terrestrial Environment

• Defining the plant kingdom
• Five key derived traits of plants
• Apical meristems
• Alternation of generations
• Walled spores produced in sporangia
• Multicellular gametangia
• Multicellular, dependent embryos

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Land vs. Water

• Some combination of characteristics allowed the
  first plants to survive and reproduce on land
  once there the many benefits of this new
  environment led to the evolution of this
  successful and diverse group of organisms
• Aerial and subterranean environments
• Aerial CO2 and light
• Soil minerals and H20
• Bright sunlight unfiltered by water or plankton
• Plenty of CO2, soil rich in nutrients
• Initially few herbivores and pathogens

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APICAL MERISTEMS

• Figure 29.5a (!)
• Localized regions of cell division at the tips of
  roots and shoots
• Produce roots and leaf-bearing shoots
• Structural specialization that allows plants to
  flourish in separate aerial and subterranean
  environments

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ALTERNATION OF GENERATIONS

• Figure 29.5b (!)
• Also evolved in various groups of algae but does
  not occur in the charophyceans
• In some groups of plants the gametophyte
  generation is dominant, in others the sporophyte
• In flowering plants, the gametophyte generation
  is highly reduced

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WALLED SPORES PRODUCED IN SPORANGIA

• Figure 29.5c (!)
• Spores are produced in organs called sporangia
• Spore walls are enriched with sporopollenin
• Allows them to survive the dry terrestrial
  environment
• Charophycean sporopollenin protects the zygote,
  and they lack sporangia

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MULTICELLULAR GAMETANGIA

• Figure 29.5d(!)
• Gametes are produced in multicellular organs of
  the gametophyte called gametangia
• Male antheridia
• Female archegonia
• The sperm fertilizes the egg in the archegonia,
  and that is where the zygote develops

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MULTICELLULAR, DEPENDENT EMBRYOS

• Figure 29.5e(!)
• The embryo (developing young sporophyte) is
  retained within the tissues of the female parent
• Nutrients are transferred from parent to embryo
  through placental transfer cells
• This is why land plants are embryophytes

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Other Terrestrial Adaptations
Cuticle

• Have evolved in many but not all plant species
• An epidermal covering known as a cuticle prevents
  dessication
• Secondary compounds such as
• Alkaloids, terpenes, and tannins defend against
  herbivores and parasites
• Flavenoids absorb harmful UV rays
• Phenolics prevent bacterial infections

Tannins
Lignin a phenolic
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Origin and Diversification of Plants

• Fossilized sporophyte tissue molecular evidence
  place the origin of plants at 475 MYA
• The first plants were nonvascular
• There have been three subsequent major
  evolutionary adaptations or adaptive radiations
  of plants
• Vascular plants evolved 420 MYA
• Seed plants evolved 360 MYA
• Flowering plants evolved 130 MYA

Figure 29.7 (!) Highlights of Plant Evolution
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Highlights of Plant Evolution

• Nonvascular and all subsequent plants have the
  five key terrestrial features
• Vascular plants have complex vascular tissue
  systems composed of xylem and phloem
• Seed plants package their embryos with a supply
  of nutrients into a seed
• Flowering plants develop their seeds inside a
  chamber called the ovary

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Some Examples of Land Plants
Pterophytes and Lycophytes
Bryophytes
Lycopodium a club moss
Pallavicinia a thalloid liverwort
Psilotum a whisk fern
Porella a leafy liverwort
Equisetum - a horsetail
Phaeoceros - a hornwort
Polypodium vulgare a fern
Polytrichum commune star moss
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Some Examples of Land Plants
Gymnosperms
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Some Examples of Land Plants
Angiosperms 250,000 species!