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Plants
• Herbaceous (nonwoody)
Plant Form and Function
• In temperate climates, aerial parts die back
• Woody
• In temperate climates, aerial parts persist
Chapter 17
The Plant Body
Functions of:
• Flowering plants can be divided into two
groups:
Roots
Stem
Leaves
Leaves
Stems
Roots
Monocots
Flowers
– Monocots: grasses, lilies, palms, and orchids
– Dicots: deciduous trees, bushes, and many
garden flowers
Tissue Systems
Seeds
•
embryo
Flower parts are in
threes or multiples
of three
Leaves have smooth
edges, often narrow,
with parallel veins
Vascular bundles
are scattered
throughout the stem
Monocots have a
fibrous root system
The seed has one
cotyledon (seed leaf)
Dicots
embryo
Flower parts are in
fours or fives or multiples
of four or five
cotyledons
Leaves are palmate
(handlike) or oval
with netlike veins
Vascular bundles
are arranged in a
ring around the stem
Dicots have a
taproot system
Integrated throughout the plant body
•
cotyledon
•
provide continuity from organ to organ
Plant body has 3 tissue systems
1. ground
2. vascular
3. dermal
The seed has
two cotyledons
(seed leaves)
Fig. 17-2
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Ground Tissue: Parenchyma Tissue
Ground Tissue System
• Consists of 3 tissues, many functions
• parenchyma tissue
• collenchyma tissue
• sclerenchyma tissue
• Composed of living parenchyma cells
• with thin primary cell walls
• Functions
• photosynthesis
• storage
• Secretion
Ground Tissue: Collenchyma Tissue
• Consists of collenchyma cells
• with unevenly thickened primary cell walls
Vacuole
• Provides flexible structural support
• Strings of celery
Nucleus
Intercellular
space
Cytoplasm
Cell wall
Parenchyma cells
Fig. 32-4a, p. 706
Thickened corner
of cell wall
Ground Tissue: Sclerenchyma Tissue
• Composed of sclerenchyma cells
• sclereids or fibers
Thick cell walls
• Sclerenchyma cells often dead at maturity
• provide structural support
Nucleus
Cytoplasm
Vacuole
Collenchyma cells
Fig. 32-4b, p. 706
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Vascular Tissue System
• Conducts materials throughout plant body
Lumen
• Provides strength and support
Cell wall
Sclerenchyma cells
Fig. 32-4c, p. 706
Xylem
Vascular Tissue: Xylem
End wall with
perforations
• Complex tissue, conducts water and dissolved
minerals
Pits
• 2 types of cells of xylem
• tracheids
• vessel elements
Cell wall
Lumen
(a) Tracheid.
(b) Vessel
element
Fig. 32-5ab, p. 708
Phloem
Vascular Tissue: Phloem
Sieve plate
with pores
• Complex tissue, conducts sugar in solution
• 2 types of cells of phloem
1. sieve tube elements
2. assisted by companion cells
Sieve tube
element
Phloem
parenchyma
cells
Lateral sieve
area
Plasmodesma
Companion cell
(c) Sieve tube
element.
(d) Phloem
tissue.
Fig. 32-5cd, p. 708
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Dermal Tissue: Epidermis
Dermal Tissue System
• Outer protective covering of plant body
• Waxy cuticle reduces water loss
• secreted by epidermis covering aerial
parts
• Epidermis:
• complex tissue
• covers herbaceous plant body
• Stomata permit gas exchange
• between shoot system and atmosphere
• Periderm:
• complex tissue
• covers woody parts of plant body
• outgrowths or hairs
• many sizes, shapes, and functions
Primary Growth
Growth in Plants
• Increase in stem or root length
• occurs in all plants
• Apical meristems
• at tips of roots and shoots
• within buds of stems
• Localized in specific regions (meristems)
• Involves 3 processes:
- cell division
- cell elongation
- cell differentiation
• Responsible for primary growth
• Primary Growth vs. Secondary Growth
Herbaceous Stems
Root hairs
Area of cell
maturation
• Epidermis: protective layer covered by a waterconserving cuticle
• Xylem: conducts water and dissolved minerals
• Phloem: conducts dissolved sugar
• Cortex, pith, and ground tissue:
– function primarily for storage & support
Area of cell elongation
Root
cap
Apical meristem
(Area of cell division)
Fig. 32-7, p. 710
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Herbaceous Stems
Basic Tissues in Herbaceous Stems
• Herbaceous eudicot stems
– vascular bundles arranged in a circle (in cross
section)
– distinct cortex and pith
• Monocot stems
– vascular bundles scattered in ground tissue
Pith
Cortex
Ground
tissue
Herbaceous Dicot Stem
Monocot Stem
(meristematic)
Ground tissue
Vascular
bundles
Epidermis
500 µm
Fig. 34-3a, p. 734
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Cortex cells
Monocot Root
Endodermis
cell
Pericycle cell
Phloem cell
Xylem vessel
elements
25 µm
dicot root
Fig. 35-3b, p. 751
Apical
meristems
Primary
tissue
Lateral
meristems
Primary xylem
Vascular
cambium
Meristematic
cells
Primary phloem
Secondary
tissues
Secondary
xylem (wood)
Secondary
phloem
(inner bark)
Cortex
Cork
cambium
Periderm
Pith
Secondary Growth
• Increase in stem or root girth (thickness)
• Woody plants only!
• Mitosis of meristematic at leteral
meristems (not apical meristems)
• throughout length of older stems and
roots
• Two Lateral Meristems responsible for
secondary growth
1. vascular cambium
2. cork cambium
Epidermis
Cork cambium: outer = cork cells; inner = cork parenchyma
cork cells & parenchyma = PERIDERM
Inner bark (secondary phloem)
Secondary Growth
• Production of secondary tissues, wood, bark
– occurs in some flowering plants (woody
dicots) and all cone-bearing trees
• Vascular cambium divides in two directions
– secondary xylem (to the inside)
– secondary phloem (to the outside)
Bark
Wood
(secondary xylem)
Vascular cambium
Fig. 32-9, p. 712
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Vascular
Cambium
Primary
xylem
Epidermis
Cortex
Primary
phloem
Vascular
cambium
Pith
Fig. 34-4a, p. 735
Remnant
of primary
phloem
Remnant
of cortex
Remnant of
epidermis
Secondary phloem
(inner bark)
Periderm
(outer bark; remnants
of primary phloem,
cortex and epidermis
are gradually crushed
or turn apart and
sloughed off)
Secondary xylem
(wood)
Secondary xylem
(wood)
Periderm
(outer bark)
Remnant of
primary xylem
Remnant of
pith
Vascular
cambium
Secondary phloem
(inner bark)
Remnant of
Remnant of
primary xylem pith
Vascular
cambium
Fig. 34-4b, p. 735
Time
2P1P
Secondary xylem
Secondary phloem
1X 2X
1X
• Lateral meristem that produces “bark”
– cork parenchyma and cork cells
2P1P
1X2X3X
1X2X
Cork Cambium
2P1P
1X2X3X4X
1P
1P
1X
Fig. 34-4c, p. 735
Second division of vascular
cambium forms a phloem cell.
Division of vascular cambium
forms two cells, one xylem cell
and one vascular cambium cell.
• Cork cells (cork)
– to outside of cork cambium
• Cork parenchyma
– to inside of cork cambium
– primarily for storage in a woody stem
Vascular cambium cell when
secondary growth begins.
Vascular cambium cell
Fig. 34-5, p. 736
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Primary
Pith xylem
Annual ring of
secondary xylem
Secondary
xylem (wood)
Heartwood
Vascular
cambium
Secondary
phloem
Sapwood
Periderm and
remnants of primary
phloem, cortex, and
epidermis
Expanded
phloem ray
Xylem ray
0.5 mm
Fig. 34-6, p. 737
Cross section of
3-year-old Tilia
stem
Fig. 34-8, p. 739
Palisade
mesophyll
Vein
(vascular
bundle)
Spongy
mesophyll
Secondary
phloem
Vascular cambium
Cuticle
Upper
epidermis
Summerwood
Springwood
Bundle
sheath
Xylem
Phloem
Annual
ring of
xylem
Stoma
Airspace
Summerwood of
preceding year
Lower
epidermis
100 µm
Stoma
Fig. 34-9, p. 739
Open
Guard
cells
Closed
Guard cells
Fig. 33-3, p. 718
Stoma
Subsidiary
cells
Fig. 33-7a, p. 722
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Transport
Water Movement
Most water that plant
absorbs is transpired
into atmosphere.
Sugar molecules from photosynthesis
are transported in phloem throughout
plant, including into roots.
• Water and dissolved minerals move from soil into
root tissues (epidermis, cortex)
Once inside roots, water
and minerals are
transported upward in
xylem to stems, leaves,
flowers, fruits, and seeds.
• Water and minerals move upward, from root xylem to
stem xylem to leaf xylem
• Water entering leaf exits leaf veins and passes into
atmosphere (Transpiration)
Roots obtain water
and dissolved
minerals from soil.
Stepped Art
Fig. 34-10, p. 740
Tension–Cohesion Model
• Explains rise of water
– even in the tallest plants!
• Transpiration
– evaporative pull causes tension at top of plant
• Column of water pulled up through the plant remains
unbroken
– due to cohesive (together) and adhesive (others)
properties of water
Sugar Translocation
• Dissolved sugar is moved upward or
downward in phloem
– from source area of excess sugar (usually
a leaf)
– to a sink (area of storage or sugar use:
roots, apical meristems, fruits, seeds)
• Sucrose is predominant sugar transported in
phloem
Source
Pressure–Flow Hypothesis
• Explains movement of materials in phloem
• Companion cells actively load sugar into
sieve tubes at source
– requires ATP
• ATP energy pumps protons out of sieve tube
elements
ATP
Pressure-flow theory
Sucrose loaded and
unloaded requires ATP
Water moves osmotically
Sink
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