Plant Diversity I:

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Chapter 29 Plant Diversity I How Plants
Colonized Land
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I.  Overview of land plant evolution            
A.  Four main groups of land plants               
          ? Groups are distinguished from algae
by reproduction (life cycle) that involves the
development of a multicellular embryo attached to
the mother plant for its protection and
nourishment.
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• B.  Charophyceans are the green algae most
  closely related to land plants.
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• 1.  Both charophyceans and land plants are
  multicellular, eukaryotic, photoautotrophs.  
• 2.  Both have rosette cellulose-synthesizing
  complexes.  Rosette cellulose-synthesizing
  complexes are rose-shaped arrays of proteins that
  synthesize the cellulose components that make up
  plant cell walls. 
• Presence of peroxisome enzymes.
• Both have similarly flagellated sperm
• Both use phragmoplasts when creating cell plates.

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• Because all these features are shared between the
  groups, both land plants and charophyceans must
  have a common ancestor.
• Figure 29.2 (p. 578) Charophyceans, closest
  algal relatives of the plant kingdom. (Fig. 29.3,
  Ed. 7)

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• 1.  Bryophytes liverworts, hornworts, mosses
•                                    
• Bryophytes do not have vascular tissues.
•  
• The next three groups are all vascular plants. 
  Vascular plants have cells that are joined to
  produce tubes that transport water and nutrients
  throughout the plant.
• Bryophytes live in damp/moist environments and
  are small so they dont need vascular tissue. 
  They are sometimes called non-vascular plants.
• Algae that we saw in last chapter live in water
  and dont need vascular tissue because nutrients
  come from surrounding water.

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The vascular plants are, in order of their
evolution 2.  Pteridophytes ferns,
horsetails, lycophytes     a.  seedless
plants 3.  Gymnosperms conifers,
ginkgo      a.  early seed plants      b. 
produce naked seeds   4.  Angiosperms flowering
plants       a.  seeds protected by growing in
ovaries       b.  majority of modern plants are
in this group    Figure 29.1 (p. 577, Ed. 6 Fig.
29.7, Ed. 7) Some highlights of plant
evolution.
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In order to grow on land, the land plants needed
to evolve terrestrial adaptations to survive (pp.
576-577, Ed. 7). C.  Terrestrial adaptations can
be used to distinguish land plants from
charophycean algae. These adaptations
are                         1.  Apical
meristems                                    
a.  Apical meristems are localized areas of cell
division at tips of roots and shoots.             
            Figure 29.3 (p. 579, Ed. 6) Apical
meristems of plant shoots and roots.
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2.  Multicellular, dependent embryos              
                       a.  Embryo develops
within female tissue female plant provides
nutrition (sugars, proteins).   Figure 29.4 (p.
579, ed. 6 p. 577, ed. 7)                       
              b.  Placental transfer cells that
enhance the transfer of nutrients from the parent
to the embryo.   Figure 29.5 (p. 579, ed. 6 p.
577, ed. 7)
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3.  Alternation of generations                    
                 Two multicellular body
forms                                     a. 
Gametophyte (haploid) that produces gametes. 
Gametes fuse to form zygotes that develop
into   b.  Sporophytes (diploid) that produce
spores.  Spores are haploid cells that can
develop into a new organism without fusing with
another cell.   Figure 29.6 (p. 580, ed. 6)
Alternation of generations  a generalized
scheme.
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 4.  Spore walls contain sporopollenin            
                         a.  Sporopollenin is a
polymer that makes the walls of plant spores very
tough and resistant to harsh conditions.   b. 
Sporopollenin is the most durable organic
material known.   c.  Spores are produced by
sporangia (cells in the sporophyte) through the
process of meiosis.   d.  Durable spores are an
adaptation for surviving on land. Can withstand
long periods of adverse conditions. Easily
transported by wind and water.    Figure 29.7 (p.
580, ed. 6) A fern spore.
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5.  Multicellular gametangia                      
               a.  Gametangia are the
gametophyte forms of bryophytes, pteridophytes,
and gymnosperms.  Gametes are produced within
these organs.                                    
b.  Female gametangia are called archegonia à
(produce and retain egg cells)   c.  Male
gametangia are called antheridia à (produce
sperm)   Figure 29.9 (p. 581) Gametangia.
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6.  Other terrestrial adaptations common to many
land plants                                    
a.  Epidermis covered by a waxy cuticle to
prevent excess loss of water.  Pores (stomata) in
cell layer can be opened and closed to allow O2
out and CO2 in.   Figure 29.10 (p. 581, ed. 6)
Cuticle of a stem from Psilotum (a pteridophyte).
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b.  Except for bryophytes, land plants have
vascular tissue in roots, stems, and
leaves.                                           
      - Xylem consists of dead cells that carry
water and nutrients from roots to the rest of the
plant.                                            
     - Phloem consists of living cells that
distribute sugars and amino acids throughout the
plant.   Figure 29.11 (p. 582, ed. 6) Xylem and
phloem in the stem of Polypodium, a fern (a
pteridophyte).
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II.  Origin of land plants             A. 
Theory is that land plants evolved from
charophycean algae over 500 million years ago. 
Charophycean algae inhabit shallow waters and
need to survive when water levels drop.  Lead to
increasing ability to survive entirely on dry
land.                        
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B.  Alternation of generations in plants may have
originated by delayed meiosis                     
    Zygote à Sporophyte à Many, many
spores   1.  Occurs on land because its more
difficult to produce zygotes.  (No water for
swimming sperm)   2.  By producing sporophyte,
many gametophytes can be produced from one zygote
because many, many spores are produced.  This
maximizes output of sexual reproduction.
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III.  Bryophytes             A.  Gametophyte is
the dominant generation in the life cycles of
bryophytes    Figure 29.15 (p. 585, ed. 6)
Figure 29.9 (p. 582, ed. 7)
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            B.  Life cycle of bryophytes          
   Figure 29.16 (p. 586, ed.6) The life cycle
of Polytrichum, a moss. (Fig. 29.8, p. 581, ed.
7)                           1.  Bryophyte
sporophytes produce and disperse huge numbers of
spores.
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C.  Ecological and economic benefits of
bryophytes                         1. 
Bryophytes were the worlds only plants for 100
million years.   2.  Peat bogs are made mostly of
moss called sphagnum.  They contain 400 billion
tons of carbon and cut down the amount of
greenhouse gases. Peat is harvested, dried, and
used as a fuel.   3.  Sphagnum is harvested for
use as a soil conditioner and plant packing
material.    Figure 29.19 (p. 588) Sphagnum, or
peat moss.
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IV.  Origin of vascular plants             -
Pteridophytes ferns               -
Gymnosperms fir trees             - Angiosperms
flowering plants   A.  Vascular plants evolved
additional terrestrial adaptations                
         1.  Xylem and phloem 2.  Dominant
sporophyte generation independent of the
gametophyte ? Different from the bryophytes   B. 
Cooksonia evolved over 400 million years ago à
oldest known vascular plant                       
  Figure 29.20 (p. 589) Cooksonia, a vascular
plant of the Silurian.
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V.  Pteridophytes  seedless vascular
plants               Figure 29.21 (p. 590, ed. 6)
Examples of pteridophytes (seedless vascular
plants). Called Pterophytes (Fig. 29.14, p. 587,
ed. 7)
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            A.  Pteridophytes provide clues to
evolution of roots and leaves                     
    1.  There is evidence that roots evolved
from subterranean portions of stems.   2.  There
are two types of leaves                          
           a.  Leaves of lycophytes are
microphylls.  Microphylls are small leaves with a
single, unbranched vein.   b.  Leaves of other
modern vascular plants are megaphylls. 
Megaphylls are typically larger and have a
branched vascular system.   Figure 29.22 (p. 591,
ed. 6 Fig. 29.13, p. 586, ed. 7) Hypotheses
for the evolution of leaves.
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B.  Sporophyte-dominant life cycle evolved in
seedless vascular plants (Pteridophytes)          
               1.  Alternation of
generations   2.  Dominant sporophyte versus
dominant gametophyte in bryophytes.   3.  Plants
are dispersed to new environments as spores no
seeds present                         Figure
29.23 (p. 592, ed. 6 Fig. 29.12, p. 585, ed. 7)
The life cycle of a fern.
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 C.  Importance of Pteridophytes                  
       1.  Dominant plants in Carboniferous
period   Figure 29.25 (p. 594, ed. 6 Fig. 29.15,
p. 588, ed. 7) Artists conception of a
Carboniferous forest based on fossil
evidence.   2.  Extensive beds of coal from these
plants
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