The origin of Embryophytes

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The origin of Embryophytes
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Embryophyte and cuticle
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Reduction of Gametophyte
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Sporophyte Advantage

• Having 2 copies of each chromosome enables
  mutations to exist without resulting in death.
• There is more UV over land than in water.
• As plants evolved the gametophyte has been
  reduced.

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Mature sporophyte (spore-producing structure and
stalk), still dependent on gametophyte.
Sporangium
Zygote grows, develops into a sporophyte while
still attached to gametophyte.
zygote
Diploid Stage
Fertilization
Meiosis
Haploid Stage
Spores form by way of meiosis and are released.
Sperm reach eggs by moving through raindroips or
film of water on the plant surface.
Spores germinate. Some grow and develop into male
gametophytes.
Antheridium
rhizoid
sperm-producing structure at shoot tip of male
gametophyte.
egg-producing structure at shoot tip of female
gametophyte.
Other germinating spores grow and develop into
female gametophytes.
Archegonium
Fig. 22.5, p. 345
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Lignin in cell walls
Embryophyte and cuticle
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Tracheid Cells

• Primitive xylem cells that have 2 functions
• Support (secondary cell walls with lignin)
• Water transport
• Many older resources call all vascular plants
  tracheophytes

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Tracheid Advantages

• Plants can now grow taller because
• They can support the mass
• They can transport water throughout the plant.

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Vascular tissues

• Xylem- dead and hollow transport of water up and
  through plants
• Phloem- contains living cells (companion and
  sieve tube) to transport sugar from
  photosynthetic cells to the rest of the plant.
• Both types are often found bundled together for
  transport efficiency

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Fern Life Cycle
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Seeds Pollen
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Gymnosperms

• Naked Seed Plants-
• Pollen- delivers sperm (microspore) to the
  archegonium (ovule/ megaspore) without water!
  Uses wind for fertilization
• Seeds. Protect the embryo and allows the
  sporophyte to grow farther from the parent with
  its added initial supply of food.

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Seeds
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Flowers Vessel Elements
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Xylem changes

• Tracheid cell diverged into 2 different- more
  specialized cells
• Vessel elements for water transport
• Fiber cells for support

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Flowers

• By attracting pollinators the flowers get pollen
  delivered directly to new flowers. This avoids
  the randomness of wind.
• The ovary of a flower will also develop into
  fruits around the seeds dispersal mechanisms.

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Perfect Flower

• Perfect flowers have both male and female
  gametangia.
• Imperfect flowers only have one sex.
• Pistil carpel

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Zoom in on the megaspore
Meiosis
Fertilization
Mitosis
Pollen Tube
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Transpiration
Click to view animation.
animation
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Stomata regulation
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Pressure flow- bulk transport
Click to view animation.
animation
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Companion cells
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Source to Sink Flow

• While most people think of sugar flowing from the
  leaves to the roots, sometimes the direction of
  flow is the opposite.

Click to view animation.
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Seed Formation

• Double fertilization produces the 2n
  zygote-embryo, and the 3n endosperm source of
  food for the embryo.

Fertilization animation.
Endosperm animation.
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Germination Imbibition

• When water enters the seed the swelling triggers
  the release of growth hormones gibberellins (GA
  gibberellic acid) This triggers the activation
  of other enzymes like amylase to start breaking
  down the stored food in the endosperm so the
  embryo can grow.

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Seedling growth

• Once the seed breaks dormancy through imbibition,
  there are a few ways in which the seedling can
  grow

Growth animation.
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Tropisms

• Because plants are sessile and do not really
  move, they can direct their growth towards a
  signal like light, gravity, or touch.
• Phototropism Grows towards light.
• Gravitropism Roots grow downwards.
• Thigmotropism Growth directed by touch.

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Phototropism

• The growth hormone Auxin is active on the dark
  side, causing them to grow longer while the side
  on the light dose not grow.

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Went (1926)
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Gravitropism

• Shoots can grow upwards while roots grow down.
  Uses auxin just like phototropism, and
  statoliths which are dense and settle to the
  bottom of the cell.

Gravitropism animation.
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Thigmotropisms

• The side exposed to touch dose not grow, while
  the side not being touched elongates.
• Trees can grow towards wind, so that the wind
  isnt blowing the tree over.
• Vines and tendrils can wrap themselves around an
  object.

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Secondary growth

• The annual thickening of branches and trunks from
  the vascular cambium puts a new layer of
  secondary xylem in the wood- creates annual
  growth rings.

Growth rings animation.
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Tree ring thickness

• Annual growth rings are good for documenting
  environmental conditions when humans have not
  been around.
• Precipitation and climate- more rain thicker
  rings, droughts thin rings.
• Fires- scars can be found within rings.

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Antagonistic growth hormones
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Apical Dominance

• Pruning the apical bud removes auxin and the
  lateral buds start growing.

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Pruning for Shade and Fruit trees.

• Notice the remaining branches are more spread out
  and lager. This results in larger shade areas.

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Pruning for dense foliage- shrubs

• The lack of apical dominance results in more
  lateral bud development.

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Photoperiods
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Phytochromes
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