INTRODUCTION%20TO%20PLANTS

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INTRODUCTION TO PLANTS
Plants evolved in terrestrial environments from a
green algae ancestor which itself was presumably
adapted to very shallow waters, ones prone to
drying. Things in common
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A. Both have chlorophylls A B and
carotenoids B. Both use starch as their primary
carbohydrate food reserve. And both deposit it in
the chloroplasts, not the cytoplasm as in other
algal groups
Chlorophyll a is a green pigment that absorbs red
and blue-violet light. Chlorophyll b absorbs
wavelengths in the blue and red-orange parts of
the spectrum.

• All photoautotrophs contain carotenoids, which
  absorb blue-violet and blue-green wavelengths
  that are missed by the chlorophylls. They reflect
  wavelengths which are red, orange, and yellow.

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C. Cellulose is the principle component of the
cell walls in plants. Likewise many green algae
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• All true plants are oogamous. Some green algae
  are also oogamous.
• - one gamete is large and non-motile one gamete
  is small and motile
• E. All true plants have an alternation of
  generations. So do many green algae-

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• Why move onto the land?
• Abundant and more consistent light for
  photosynthesis
• More plentiful and freely circulating CO2
• lack of competition from other organisms
• More surface area on leaves exposed to sun!

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Plant terrestrial adaptations

• "Living on land poses very different problems
  from living in the water. As plants have adapted
  to the terrestrial environment, complex bodies
  with extensive specialization of cells for
  different functions have evolved."

These innovations include
Waxy cuticle  Stomata
Vascular tissue Woody tissue (lignin)
Pollen      Development of the sporophyte as the dominant generation
Seeds Flowers AND Fruit
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Challenges during Algae-to-Plant Transition Challenges during Algae-to-Plant Transition
Algae Plants
Minerals absorbed from water Water from water Sunlight received within water Weight supported by water Sperm swim through water Spores swim through water Minerals / nutrients from soil Water from soil (susceptibility to desiccation) Sunlight received above soil (products require transport within plant) Weight not supported by air (requires internal supporting structure) air is less dense! Less water for sperm to swim through Less water for spores to swim through
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Lets imagine the first "plant" as an algae with
most of its thallus "rooted" in the water, but
with a portion lifted slightly above the water,
or extending slightly past the shoreline, in a
effort to better compete against its fellow algae
found only at and below the water line
Such an alga might not initially require a waxy
cuticle (since water would always be available
from the portion of the organism found below the
water line),
but might have given those individuals who first
displayed such a cuticle above the water line
less of a requirement for water. Thus the alga
could move beyond the water therefore allowing
slightly greater height and extension out over
the shore
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Once a waxy cuticle was in place, diffusion of
gasses could limit overall plant height (or
spreading beyond the water), thereby selecting
for small holes (stomata) in the waxy cuticle
In an effort to better control moisture
retention, it would be beneficial for the
organism to selectively open and close the holes
Such a algae could be essentially preadapted at
this point to existing in the presence of less
water, e.g., periodic desiccation due to
fluctuating water levels
At some point during the above sequence we
essentially have seen the transition from status
as a green alga to that of a moss
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WAXY CUTICLE

• The transition from a watery environment to a
  terrestrial one most obviously involves an
  exposure to air
• Air is drying (unless relative humidity is 100
• The cuticle prevents dessication

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• Stomata (singular, stoma)
• The trouble with a waxy cuticle is that along
  with waterproofing comes air-proofing
• Thus, the waxy cuticle prevents the diffusion
  of O2 and CO2 into and out of the plant,
  interfering with carbon fixing as well as
  cellular respiration
• The innovation that solved this dilemma were
  small, opening and closing holes, called stomata,
  through which gasses can diffuse into and out of
  the plant
•           

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Embryophyte

• A new mode of reproduction was needed to solve
  the land issue
• Nonaquatic environment gametes produced in
  gametangia - - -
• Eggs fertilized with in female organ
• Embryo retained in female

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ALTERNATION OF GENERATIONS

• Haploid gametophyte produces and alternates with
  diploid sporophyte.
• Sporophyte the produces gametophytes.

These two types of plants are HETEROMORPHICmeanin
g they differ in structure.
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http//www.nova.edu/ocean/biol1060/plants.html
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GAMETOPHYTE Produces sperm and egg (hence,
gamet-o-phyte)
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SPOROPHTYE Produces spores (hence spor-o-phyte)
it is larger and more noticeable in all but
bryophytes!
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SPOROPHYTE grows from GAMETOPHYTE!
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4 major periods of plant evolution

• Origin from aquatic ancestors (algae) called
  charophytes
• 425 mya - Silurian period
• Cuticle
• Vascular tissue

• Ferns seedless
• 400 mya Devonian

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• Origin of Seed
• 360 mya end of Devonian
• Gymnosperm naked seed
• Seed embryo packed w/ food and resistant coat

• Flower plants with ovaries
• 130 mya cretaceous
• 1. Angiosperm angio means container

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TAXONOMY

• Based on vascular vs. nonvascular
• Divison Bryophyta mosses,
• nonvascular

2. Embryophytes that generally lack vascular
tissue and require water for reproduction
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2 adaptations made land possible

• Waxy cuticle
• Gametangia protect developing gametes
• a. Antheridium male gametangium
• b. Archegonium produces single egg

• Bryophytes are not free from aquatic habitat
• Bryophytes lack woody tissue, thus
• Gametophyte is dominant

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PTEROPHYTA

• Carboniferous period forests loaded w/ ferns
• Ferns have fronds which is a compound leaf
• Fiddlehead uncurls as leaf grows

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Seed plants

• Coniferophyta (GYMNOSPERMS)
• Earlier Fossil Record than Angiosperms
• LACK enclosed chambers where seeds develop
• Adaptations
• Leaves
• cuticle
• Male
• female

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Seed plants

• Anthophyta
• Used insects for pollination,
• Specialized vascular tissue
• Monocotyledone

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http//waynesword.palomar.edu/termfl2.htm
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DICOT VASCULAR TISSUE IN AN X
Draw these on your notes sheet
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SHALLOW WATER FIRST!

• A. Charophytes
• Drying
• Preadaptations for land
• - waxy cuticle
• - protection of gametes
• - protection of developing embryos
• Thus land-life possible
• Sunlight unfiltered by water and algae
• Soil rich in minerals
• Absence of terrestrial herbivores

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III. Vascular Tissue Breakthrough

• We talked about these on Tuesday!

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IV flower structure!

1. Gametophytes retained in moist reproductive
   tissue of sporophyte generation
2. POLLINATION no longer need water for
   fertilization
3. Seed replaces spore

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Use your book or the computer to label/define the
flower parts! These are REALLY important!
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Problems with pollination and/or fertilization
can cause fruit disorders such as "cat facing."
If pollen is not evenly distributed on the
stigma, all the ovules are not fertilized,
preventing sections of the new fruit from
developing
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Aggregate fruit
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Multiple fruit -
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• Look this last part up! How did animals and
  angiosperms coevolve?