Plant Diversity I: The Colonization of Land

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Plant Diversity I The Colonization of
Land

• Campbell, 5th Edition, Chapter 29
• Nancy G. Morris
• Volunteer State Community College

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Figure 29.3
Highlights of Plant Evolution
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Review of Characteristics

• Chloroplasts with photosynthetic pigments
  chlorophyll a, chlorophyll b, carotenoids
• Cell walls containing cellulose
• Secondary cell walls containing lignin
• Food stored as amylose in plastids
• Classification of Kingdom (Table 29.1)

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Plant Kingdom

• Members show structural, chemical, reproductive
  adaptations of terrestrial life
• This distinguishes higher plants from the aquatic
  algae
• Structural adaptation includes specialized
  structures to obtain water, minerals, carbon
  dioxide, light, etc.
• Example stomata special pores on surface for
  gas exchange

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Plant Kingdom

• Chemical adaptation includes a waxy cuticle,
  composed of cutin, to prevent desiccation
• Cutin, lignin, sporopollenin are examples of
  secondary products meaning that they are produced
  through metabolic pathways not common to all
  plants
• cellulose is an example of a primary product

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Plants as EmbryophytesA new mode of
reproduction was necessary to move from an
aquatic to terrestrial existence

• 1) Gametes are produced in gametangia, organs
  with protective jackets of sterile cells that
  prevent gametes from drying out. Egg is
  fertilized within the female organ.
  Figure 29.1a

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Plants as Embryophytes

• 2) Embryos must be protected against
  desiccation. Zygote develops into embryo that is
  retained within female protective cells in the
  gametangia Figure 29.1b

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Alternation of Generations a review

• All higher green plants reproduce sexually
• Most are also capable of asexual reproduction
• The haploid gametophyte generation produces and
  alternates with a diploid sporophyte generation.
  The sporophyte produces gametophytes.

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Figure 29.2Alternationof Generation
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Alternation of Generations a review

• The life cycle is heteromorphic the gametophyte
  sporophyte differ in morphology
• The sporophyte is larger more noticeable in all
  but the bryophytes
• Reduction of the gametophyte and dominance of the
  sporophyte generation we move from bryophytes to
  angiosperms

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Figure 29.5 Hypothetical Mechanism Origin of
Alternations of Generations
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Keeping a low profile

• Bryophytes
• Lack woody tissue
• Unable to support tall plants on land
• Often sprawl horizontally as mats

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Nonvascular Plants 3 Divisions
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Division Bryophyta

• Bryon (Gr. moss)
• Grip substratum with rhizoids
• Cover about 3 of land surface
• Contain vast amounts of organic carbon
• Campbell, Figure 29.7, Life Cycle of a Moss

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Division Hepatophyta

• Liverworts
• Sporangia have elaters, coil-shaped cells, that
  spring out of capsule disperse spores
• Also reproduce asexually from gemmae (small
  bundles of cells that bounce out of cups when hit
  by rainwater)
• Campbell, Figure 29.8

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Division Anthocerophyta

• Hornworts
• Resemble liverworts but sporophyte is horn-shaped
  
• Photosynthetic cells have one large single
  chloroplast
• Campbell, Figure 29.9

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Adaptation to land

• Antheridium produces flagellated sperm
• Archegonium produces a single egg
• Fertilization occurs within the archegonium
• Zygote develops into an embryo within the
  archegonium (embryophyte condition)

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Ancestral aquatic habitat evident

• Water required for reproduction
• Flagellated sperm cells swim from the antheridium
  to the archegonium
• Vascular tissue is absent
• Water is distributed throughout the plant by the
  relatively slow process of diffusion, capillary
  action, cytoplasmic streaming

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Six terrestrial adaptations

• 1) Regional specialization of the plant body
• subterranean roots that absorb water minerals
  from the soil
• aerial shoot system of stems leaves to make
  food

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Terrestrial adaptations

• 2) Structural support
• support is provided by lignin embedded into the
  cellulose matrix of cell walls

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Terrestrial adaptations

• Vascular systems evolved
• XYLEM complex tissue that conducts water
  minerals from the roots to the rest of the plant
  composed of dead, tube-shaped cells that form a
  microscopic water-pipe system
• PHLOEM conducts sugars, amino acids, etc.
  throughout the plant composed of living cells
  arranged in tubules

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Terrestrial adaptations

• 4) Pollen pollination eliminated the need for
  water to transport gametes
• 5) Seeds
• 6) Increased dominance of the diploid sporophyte

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Vascular plants display two distinct reproductive
strategies

• Homosporous plants produce one type of spore
• Each spore develops into a bisexual gametophyte
  with both antheridia and archegonia
• Heterosporous plants produce two kinds of spores
• Megaspores develop into female gametophytes
  possessing archegonia
• Microspores develop into male gametophytes
  possessing antheridia

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Comparison

• Single Eggs
• Homosporous type of Bisexual
• Sporophyte spore gametophyte Sperm
• Female
• Megaspore Gametophyte Eggs
• Heterosporous
• Sporophyte Microspore Male Sperm
• 
  Gametophyte

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Seedless vascular plants primitive
tracheophytes

• Division Psilophyta - whisk ferns
• Division Lycophyta - club mosses
• Division Sphenophyta - horsetails
• Division Pterophyta - ferns

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Division Lycophyta

• Club mosses (Fig. 29.12)
• Sporangia are borne on sporophylls leaves
  specialized for reproduction
• In some sporoangia, sporophylls are clustered at
  branch tips into club-shaped strobili hence the
  name club moss
• Spores develop into inconspicuous gametophytes
  that are nurtured by symbiotic fungi.
• Most are homosporous. (Selaginella is
  heterosporous.)

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Division Sphenophyta

• (Fig. 29.13) Equisetum
• Common in Northern Hemisphere in damp locations
• Homosporous
• Gametophyte is only a few mm
• Gametophyte is free-living photosynthetic

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Division Pterophyta FERNS

• 12,000 existing species
• most ferns have fronds
• homosporous
• sori on underside of leaf with annulus to
  catapult spores into the air
• prothallus (gametophyte) requires water

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Figure 29.11 Life Cycle of a Fern
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Coal forests

• During the Carboniferous period, the landscape
  was dominated by extensive swamp forests club
  mosses, whisk ferns, horsetails were gigantic
  plants
• Organic rubble of the seedless plants accumulated
  as peat (Figure 29.14)
• When later covered by sea and sediment, heat
  pressure transformed the peat into coal