Transcript Growth in Plants

Chapter 35
Plant Structure and Growth
Essential Idea: Plants adapt their
growth to environmental conditions.
TOK: Plants communicate
chemically both internally and
externally. To what extent can
plants be said to have language?
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Cell Organization
•Tissues are groups of cells with a
common function.
•Tissues (or many different types)
comprise organs--they carry out
particular functions.
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3 Basic Organs
• Three basic organs
evolved to take
advantage of this
– 1. Roots
– 2. Stems
– 3. Leaves
• They are organized
into a root system
and a shoot system.
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Plant Tissue
•Plants have 3 tissue
systems:
–1. Dermal
–2. Vascular
–3. Ground
•Each plant organ has
the three tissue types.
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1. The Dermal Tissue System
•It is the outer protective covering, it’s
the first line of defense against
physical damage and pathogens.
•Non-woody plants consist of a tightly
packed tissue called the epidermis.
•Woody plants consist of protective
tissues called periderm (eventually
forming bark).
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1. The Dermal Tissue System
•The epidermis also forms the cuticle
which assists in protection, disease
prevention, and prevention of water
loss.
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2. The Vascular Tissue System
•Vascular tissue starts in
the root system.
•The root system
provides a large
surface area for
mineral ion and water
uptake.
•The roots are modified
with root hairs.
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2. The Vascular Tissue System
•The root hairs
dramatically
increase the
surface area of
the plant for
mineral and
water uptake.
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2. The Vascular Tissue System
•Carries out long-distance transport of
materials between roots and shoots.
•The 2 tissues are:
–A. Xylem
–B. Phloem
•Together, they’re the stele
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Stele
• The vascular tissue of a root or
stem is called the stele.
– In angiosperms, the stele of the
root is in the form of a solid
vascular cylinder.
– The stele of the stem and leaves
is arranged into a vascular
bundle--strands consisting of
xylem and phloem.
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A. Xylem
•Xylem conveys water and dissolved
minerals upward from roots to shoots.
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A. Xylem
•The two types of water conducting
cells of xylem.
–A. Tracheids
–B. Vessel Elements:
•These are dead at functional maturity.
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A. Tracheids
• Are found in the xylem of all
vascular plants.
• Most angiosperms, a few
gymnosperms, and a few
seedless vascular plants
have vessels.
• When the cell dies, a nonliving conduit remains
through which water flows.
• The secondary cell walls
contain lignin.
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B. Vessel Elements
•Usually wider, shorter
and thinner than
tracheids.
•They are relatively
long micropipes and
are aligned end to
end.
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B. Phloem
•Phloem transports organic nutrients
from where they are made to where
they are needed (from leaves to root
tips, developing leaves and fruits).
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B. Phloem and Sieve Tubes
•The sugar conducting
cells of phloem are
alive at maturity.
•The sugar and other
organic nutrients flows
through sieve tubes.
•The end walls of sieve
tubes have sieve plates
which have pores that
allow fluid to move
from tube to tube.
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Companion Cells
•Sieve tubes have companion cells
that help to load sugars into sieve
tube members.
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3. Ground Tissue
• The ground tissue system provides
for storage, photosynthesis and
support.
• The ground tissue system comprises
tissues that are neither dermal nor
vascular.
• Pith is ground tissue internal to the
vascular tissue.
• The cortex is ground tissue external
to the vascular tissue.
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Meristems
•Dicotyledonous plants have apical
and lateral meristems.
•Meristems contain perpetually
embryonic cells.
•There are two main types:
–1. Apical
–2. Lateral
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1. Apical Meristem
•The apical meristem is located at the tips
of roots and in the buds of shoots.
•Mitosis in this area enables primary growth,
extension of the stem and development
of leaves. (length).
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Hormones
•Plant hormones control the growth in the
shoot apex.
–Auxins-initiates growth of roots and
development of fruits and leaf development.
–IAA-controls growth of shoot apex, promotes
elongation in stem cells. IAA is synthesized in
the apical meristem and is transported down
for stem growth.
–Cytokines-produced in root, promotes axillary
growth.
–Gibberellins-contributes to stem elongation.
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Tropisms
•Plant shoots also respond to the
environment by tropisms.
–Phototropism-growth towards light.
•The absorption of light by photoreceptors can
control the transcription of specific genes.
–Gravitropism-growth in response to
gravitational force.
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2. Lateral Meristem
•After the primary growth from the
apical meristem has stopped, the
remaining growth is mostly all
secondary (girth).
•There are two main types of lateral
meristems that increase the girth of
the plant.
–A. Vascular cambium
–B. Cork cambium
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A. Vascular Cambium
•Adds layers of
vascular tissue to the
woody plant.
•Secondary xylem
(wood)
•Secondary phloem
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A. Vascular Cambium
•From year to year the
vascular cambium can
be seen as rings on a
transverse section of a
woody plant.
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B. Cork Cambium
•Replaces the epidermis with periderm
which is thicker and tougher.
•Produces cork and provides a
protective tissue layer for the plant.
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Primary and Secondary
Growth
•Viewing a transverse section, the
vascular cambium appears as a ring.
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Primary Growth
•Recall, primary
growth produces
the main plant
body.
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Secondary Growth
•Secondary growth
continues over the
years and layers of
wood accumulate
(secondary xylemtracheids, vessel
elements and
fibers.)
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Secondary Growth
•This secondary
growth increases
the diameter of
the tree each
year.
•Counting these
layers tells you
the age of the
tree.
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Secondary Growth
•Secondary growth
is due to the
division of the
vascular
cambium.
•The vascular
cambium
produces 2° xylem
to the inside, and
2° phloem to the travismulthaupt.com
Secondary Growth
•Secondary growth
is also due to the
division of the cork
cambium.
•The cork cambium
produces some
cells that grow
inward, and a lot
of cells that grow
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outward.