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Lecture 8 Outline (Ch. 35)
I.
Plant organs
A. Roots
B. Stems
C. Leaves
II.
Plant tissues
A. Dermal
B. Vascular
C. Ground
III. Plant Growth
A. Meristems
B. Primary vs. secondary
IV. Lecture Concepts
Plant “bodies”
Plants, like multicellular
animals, have organs
composed of different
tissues, which in turn
are composed of cells
Shoot
system
Leaf
Stem
Three Basic Plant Organs:
Roots, Stems, and Leaves
Root
system
Roots - Overview
• Roots need sugars from photosynthesis;
• Shoots rely on water and
minerals absorbed by the
root system
• Root Roles:
- Anchoring the plant
- Absorbing minerals and water
- Storing organic nutrients
Roots - Comparisons
Taproots:
Typical of dicots, a
primary root forms
and small branch
roots grow from it
Fibrous roots:
In monocots and seedless
vascular plants, the primary
root dies, replaced by new
roots from stem
Prop roots
Roots – Many Plants Have
Modified Roots
“Strangling”
aerial roots
Storage roots
Buttress roots
Pneumatophores
Stems - Overview
Stem: an organ made of
– An alternating system
of nodes, points at
which leaves attach
– Internodes, stem length
between nodes
• Axillary bud - structure
that can form a lateral
shoot, or branch
• Apical/terminal bud located near the shoot
tip, lengthens a shoot
• Apical dominance
maintains dormancy in
most nonapical buds
Apical bud
Node
Internode
Apical
bud
Vegetative
shoot
Axillary
bud
Stem
Shoot
system
Stems – Many Plants
Have Modified Stems
Rhizomes
Bulbs
Storage leaves
Stem
Stolons
Stolon
Tubers
Leaves - Overview
The leaf is the main photosynthetic
organ of most vascular plants
Shoot
system
Leaves generally have
Leaf
Blade
Petiole
a flattened blade
and a stalk called the
petiole, which joins the leaf
to a node of the stem
Leaves - Comparisons
Monocots and dicots differ in the arrangement of veins,
the vascular tissue of leaves
Most dicots have
branch-like veins and
palmate leaf shape
Monocots have parallel
leaf veins and longer,
slender blades
Leaves – Plants have
modified leaves for
various functions
Tendrils
Spines
Storage
leaves
Reproductive leaves
Bracts
Plant Tissues
• Each plant organ has
dermal, vascular, and
ground tissues
• Each of these three
categories forms a
tissue system
Dermal
tissue
Ground
tissue Vascular
tissue
Plant Tissues
1) Dermal Tissue System
• Outer covering
• Protection
2) Vascular Tissue System
• “Vessels” throughout plant
• Transport materials
3) Ground Tissue System
• “Body” of plant
• Photosynthesis; storage; support
Plant Tissues - Dermis
Dermal Tissue System (Outer Covering of Plant):
1) Epidermal Tissue (epidermis):
• Forms outermost layer
Cuticle: Waxy covering
• Reduces evaporation
• Inhibits microorganism invasion
Root Hairs: extended root surface
• Increase absorption
2) Peridermal Tissue (periderm):
• Only in woody plants (“bark = dead cells”)
• Protection; support
Plant Tissues - Dermis
Plant Tissues - Vascular
Vascular Transport System
1) Xylem (dead at maturity):
- Moves water & minerals from roots to shoots
Plant Tissues - Vascular
Vascular Transport System
2) Phloem (living at maturity)
- Moves water, sugar, amino acids & hormones
Vasculature - Comparisons
Monocots and dicots differ in the arrangement of
vessels in the roots and stems
Dicots
Monocots
Stem
Root
Plant Tissues – Ground Tissue
• Some major types of plant cells:
– Parenchyma
– Collenchyma
– Sclerenchyma
– Water-conducting cells of the xylem
– Sugar-conducting cells of the phloem
• Tissues that are neither dermal nor
vascular are ground tissue
• Ground tissue internal to the vascular
tissue is pith; ground tissue external to
the vascular tissue is cortex
• Ground tissue includes cells specialized
for storage, photosynthesis, and support
Plant Tissues - Ground
Ground Tissue System (“Body” of Plant):
1) Parenchyma (most abundant):
Thin-walled cells;
living
• plant metabolism:
Photosynthesis;
hormone secretion;
sugar storage
Parenchyma cells in
Elodea leaf,(w/chloroplasts)
Plant Tissues - Ground
Ground Tissue System (“Body” of Plant):
2) Collenchyma:
Thick-walled (uneven);
living
• Offers support
(flexible & strong)
Collenchyma cells sunflower
Plant Tissues - Ground
Ground Tissue System (“Body” of Plant):
Sclereid cells in pear (LM)
3) Sclerenchyma:
Thick, hard-walled; Dead
• Offer support
(e.g. hemp fibers;
nut shells)
Cell wall
Fiber cells in ash tree
Plant Tissues - Vascular
1) Xylem (dead at maturity):
A)
B)
Vessel
Tracheids: Narrow, tube-like cells
Vessel Elements: Wide, tube-like cells
Tracheids
100 µm
Pits
Tracheids and vessels
Perforation
plate
Vessel
element
Vessel elements, with
perforated end walls
Tracheids
Plant Tissues - Vascular
2) Phloem (living at maturity)
A) Sieve Tubes: Wide, tube-like cells
B) Companion Cells: support and regulate
Sieve-tube elements:
sieve tubes
3 µm
longitudinal view
Sieve plate
Sieve-tube element (left)
and companion cell:
cross section
Companion
cells
Sieve-tube
elements
Plasmodesma
Sieve
plate
30 µm
10 µm
Nucleus of
companion
cells
Sieve-tube elements:
longitudinal view
Sieve plate with pores
Plant Growth
Plant Growth:
1) Indeterminate: Grow throughout life
2) Growth at “tips” (length) and at
“hips” (girth)
Growth patterns in plant:
1) Meristem Cells: Dividing Cells
2) Differentiated Cells: Cells specialized in structure & role
• Form stable, permanent part of plant
Plant Growth
1) Primary Growth:
• Apical Meristems:
Mitotic cells at “tips” of roots / stems
length
1) Increased length
2) Specialized structures (e.g. fruits)
2) Secondary Growth:
girth
• Lateral Meristems:
Mitotic cells “hips” of plant
Responsible for increases in stem/root diameter
Plant Growth
Shoot apical meristem
Leaf primordia
Young
leaf
Developing
vascular
strand
Axillary bud
meristems
Plant Growth
Two lateral meristems: vascular cambium and cork cambium
Primary growth in stems
Epidermis
Cortex
Shoot tip (shoot
apical meristem
and young leaves)
Primary phloem
Primary xylem
Pith
Lateral meristems:
Vascular cambium
Cork cambium
Secondary growth in stems
Periderm
Axillary bud
meristem
Cork
cambium
Cortex
Root apical
meristems
Pith
Primary
xylem
Secondary
xylem
Vascular cambium
Primary
phloem
Secondary
phloem
Plant Growth
Stem – Secondary Growth:
• thicker, stronger stems
Vascular Cambium: between
primary xylem and phloem
primary phloem
vascular cambium
primary xylem
epidermis
Produces inside stem:
A) Secondary xylem
- moves H2O, inward
B) Secondary phloem
- moves sugars, outward
pith
cortex
primary xylem
dividing
vascular
cambium
primary phloem
Vascular Cambium:
Plant Growth
Secondary growth
secondary phloem
primary phloem
primary xylem
secondary xylem
primary
xylem
new
secondary
xylem
new
secondary
phloem
vascular cambium
dividing
vascular
cambium
primary
phloem
pith
cortex
Vascular cambium
Growth
X X C P P
X X C P
Vascular
cambium
Secondary
xylem
Secondary
phloem
X C P
C
X C
C
C
After one year
of growth
After two years
of growth
Plant Growth
Stem – Secondary Growth:
Cork Cambium:
• Located under outer surface;
produces periderm
Dead at maturity
Protection
Growth
ring
Vascular
ray
Heartwood
Secondary
xylem
Sapwood
Vascular cambium
Secondary phloem
Bark
Layers of periderm
Plant Growth
Stem – Secondary Growth:
heartwood
(xylem)
sapwood
(xylem)
vascular
cambium
phloem
annual ring
Sapwood = Young xylem, water
late
xylem
Heartwood = Old xylem, support
early
xylem
Secondary phloem = grows outward
older phloem crushed
Seasonal Growth = annual rings
Plant Growth
RESULTS
Ring-width
indexes
2
1.5
1
0.5
0
1600
1700
1800
Year
1900
2000
Using dendrochronology to study climate
Plant Growth
Living tree or dead tree?
Plant Growth - Roots
Epidermis
Cortex
Endodermis
Vascular
cylinder
Pericycle
Core of
parenchyma
cells
Xylem
100 µm
Phloem
100 µm
(a) Root with xylem and phloem in the center
(typical of eudicots)
(b) Root with parenchyma in the center (typical of
monocots)
Endodermis
Pericycle
Key
to labels
Dermal
Ground
Vascular
Xylem
Phloem
Plant Growth - Stems
• In most monocot stems, the vascular bundles are scattered
throughout the ground tissue, rather than forming a ring
Phloem
Xylem
Sclerenchyma
(fiber cells)
Ground
tissue
Ground tissue
connecting
pith to cortex
Pith
Epidermis
Key
to labels
Cortex
Epidermis
Vascular
bundle
Dermal
Vascular
bundles
Ground
1 mm
(a) Cross section of stem with vascular bundles forming
a ring (typical of eudicots)
Vascular
1 mm
(b) Cross section of stem with scattered vascular bundles
(typical of monocots)
Plant Growth - Leaves
• Leaf epidermis contains stomata - allow CO2 exchange
• Stomata flanked by two guard cells, control open vs. closed
• The ground tissue in a leaf, called mesophyll, fills the middle
Guard
cells
Key
to labels
Dermal
Ground
Cuticle
Vascular
50 µm
Stomatal
pore
Epidermal
cell
Sclerenchyma
fibers
Stoma
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Upper
epidermis
Palisade
mesophyll
100 µm
Spongy
mesophyll
Bundlesheath
cell
Lower
epidermis
Cuticle
Xylem
Vein
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Vein
Air spaces Guard cells
(c) Cross section of a lilac
(Syringa)) leaf (LM)
Lecture 8 Concepts
-
Compare monocots and dicots in terms on vasculature
in stems, leaves and roots, leaf shape, root type.
-
Describe dermal, vascular, and ground tissues
-
List the roles for roots, stems, leaves.
-
Compare xylem versus phloem – function, location,
growth.
-
Discuss differences between parenchyma, collenchyma,
sclerenchyma cells.
-
Describe primary versus secondary growth.
-
Explain what ‘bark’ is made out of – is it essential for the
tree?
-
Write out a list of new terminology and provide
descriptions