Plant Cells and Tissues An Evolutionary Perspective

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Plant Cells and Tissues An Evolutionary
Perspective
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Web Notes
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http//botit.botany.wisc.edu/Anatomy/
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Plant Cells and Tissues An Evolutionary
Perspective
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Plants are structurally complex
All the cells of a plant are genetically
identical, but the information is expressed in
different ways in different places at different
times in a synchronized fashion.
.. but plants arose from structurally simple
ancestors
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Plants Arose from the Green Algae During the
Silurian Period Over 400 Million Yeas Ago
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Evidence That Plants Arose from the Green Algae

• Pigmentation

• Cellulose in their cell walls

• Starch stored in the plastid

• Some green algae undergo cell division by means
  of a phragmoplast

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Plants have become structurally complex in
response to the challenges of life on land
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. but can be considered simply a group of the
green algae that have become adapted for life
on land.
Sequoiadendron
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Challenges for Colonizing the Land
Solutions (Adaptations)
Dehydration
--------------------gt Dermal tissue
--------------------gt Secondary Walls
Support
Transport of Water and Minerals
--------------------gt Xylem Tissue
Transport of Photosynthate
--------------------gt Phloem Tissue
Fertilization
--------------------gt To be considered later
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Vascular plants are made up of three tissue
systems which are represented in each plant
organ.
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Ground Tissue System
Includes cells and tissues like those found in
the green algae
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Dermal Tissue System - found in all plants
Dermal tissue of a Hornwort, a non-vascular
plant
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Vascular Tissue System
Are tissues that transport substances long
distances in a plant.
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Vascular Tissue System
Dermal Tissue System
Ground Tissue System
Green Algae All Plants
All Plants
Some Plants
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Ground Tissue System
Green Algae All Plants
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Ground Tissue System
Parenchyma Tissue Composed of Parenchyma Cells
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Parenchyma
Is a type of simple tissue consisting entirely of
parenchyma cells.
Parenchyma cells are living, undifferentiated
plant cells usually lacking a secondary cell
wall.
Typically, parenchyma cells are totipotent. Each
cell retains the ability to grow into a whole
plant. This makes genetic engineering much easier
with plants than with animals.
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Ground Tissue System
Parenchyma Tissue Composed of Parenchyma Cells
Function
Growth/Wound Healing/Reproduction
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Ground Tissue System
Parenchyma Tissue Composed of Parenchyma Cells
Function
Growth/Wound Healing/Reproduction
Photosynthesis
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Ground Tissue System
Parenchyma Tissue Composed of Parenchyma Cells
Function
Growth/Wound Healing/Reproduction
Photosynthesis
Storage
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Ground Tissue System
Parenchyma Tissue Composed of Parenchyma Cells
Function
Growth/Wound Healing/Reproduction
Photosynthesis
Storage
Collenchyma Tissue Composed of Collenchyma Cells
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Collenchyma
Is a simple tissue consisting only of collenchyma
cells
Collenchyma cells are living cells with thickened
primary walls. They never have secondary walls.
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Ground Tissue System
Parenchyma Tissue Composed of Parenchyma Cells
Function
Growth/Wound Healing/Reproduction
Photosynthesis
Storage
Collenchyma Tissue Composed of Collenchyma Cells
Function
Support in herbaceous tissues
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Sclerenchyma
Sclerenchyma (hard) cells develop a secondary
wall and serve to support and protect the plant.
Sclerenchyma cells are found in all three tissue
systems. In Lab, you will observe two types of
sclerenchyma cells, but we will see no examples
of pure sclerenchyma.
stone cells
And fibers
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A stone of a peach is pure sclerenchyma tissue
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Dermal Tissue System
Ground Tissue System
Green Algae All Plants
All Plants
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Dermal Tissue System
Epidermis
Basal epidermal cells excrete a cuticle - this
keeps water in..and prevents gas exchange
To survive the epidermis must be pierced with
pores. In most plants, guard cells regulate gas
exchange through these pores. Pores regulated by
guard cells are stomata
Trichomes are hairs associated with the epidermis
of the shoot
Root hairs form from epidermal cells of the root
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Dermal Tissue System
In woody plants the role of the epidermis is
taken over by a periderm that includes cork.
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Vascular Tissue System
Dermal Tissue System
Ground Tissue System
Green Algae All Plants
All Plants
Some Plants
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Vascular tissue is necessary for a plant to
become tall.
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Vascular plants have cells with secondary walls
that include lignin
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But why not simply remain short?
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Because of competition for light.
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The Vascular Tissue System includes two types of
tissues .
Phloem
Xylem
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Vascular Tissue System
Xylem Moves water and minerals up the plant
and provides support to the plant.
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Vascular Tissue System
Phloem Moves photosynthate (usually sucrose)
around the plant
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Xylem and Phloem
The evolution of xylem is a direct response to
the unique challenges of life on land relating
to water transport and support.
The evolution of phloem is not specific to the
challenges of life on land, but was simply a
response to the challenge of becoming a large
photo-autotroph. Large photo-autotrophs
invariably need to fuel a significant amount of
non-photosynthetic tissue.
These points are clearly illustrated by the
evolution of phloem in the kelps, and also by
the reduction of xylem in plants that become
adapted to life submerged in water.
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Kelps are photo-autotrophs that have become large
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Kelps are supported by water and have no need for
a tissue like xylem or cells with secondary walls
The kelp Macrocyctis
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But the lower portion of the plant becomes shaded
The kelp Macrocyctis
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And kelps have independently evolved a type of
phloem tissue
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Many groups of plants have become adapted for
life emmersed in the water
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Vascular tissue In the leaf of water lily
Vascular tissue In the leaf of lilac.
Vascular tissue of a minor vein of water lily.
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Xylem is a complex tissue that includes tracheary
elements
Tracheid
Vessel Element
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Tracheary elements are dead at maturity and have
a secondary wall.
Water moves through these cells by mass flow.
The pressure inside tracheary elements is less
than the ambient pressure and they are in risk of
collapse.
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Air pressure can only lift a column of water
about 32 feet, and yet plants grow much taller
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Cohesion-Tension Theory
Text pages 671 - 675
Water is pulled up the tracheary elements,
because water molecules stick together (cohere)
via hydrogen bonds
.
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Secondary walls keep the tracheary elements from
collapsing
Vessel elements in an elongating plant stem
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Secondary walls also help support the plant
Vessel element with a complete secondary wall
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All Tracheary elements have pits
Red secondary wall
Black primary wall
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Tracheids only have pits
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We will consider the structure of tracheids in
our lab on the gymnosperms
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A vessel element is a tracheary element with a
perforation plate
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A perforation is an area between tracheary
elements where both the primary and secondary
wall has been removed.
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Vessel elements together from a vessel
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Vessels have independently evolved in six
different plant groups.
Flowering plants have them
Conifers Dont
The examples of xylem we will see in the lab all
have vessels