Plant Structure and Function
Professor Andrea Garrison
Biology 3A
Illustrations ©2014 Cengage Learning unless
otherwise noted
Plant Structure and Function
• Previously discussed adaptations for living on
land
• Will elaborate on some of those adaptations
here, as well as discuss additional aspects of
plant structure
Plant Structure and Function
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Plant Structure and Function
• Already discussed
– Shoot system
• Leaves, stems,
reproductive structures
– Root system
• Anchorage, absorption
• Root hairs
• Also see the vascular
tissue extending
throughout plant
Plant Structure and Function
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Plant Structure and Function
• Three tissue systems
– Ground tissue system
• Most of plant body
• Functions in metabolism,
storage, support
– Vascular tissue system
• Transport
• Extends throughout roots,
stems, leaves
– Dermal tissue system
Plant Structure and Function
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Three Tissue Systems in Leaf
Plant Structure and Function
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Ground Tissues
A. Location of tissues in stem
Dermal tissue
(epidermis)
Parenchyma
Vascular tissues
Xylem
Collenchyma
Phloem
Sclerenchyma
Plant Structure and Function
Ground
tissues
6
Vascular Tissues
• Vascular system
– Provides transport
• Water & P/S products carried throughout plant
– Provides support
• Walls strengthened with lignin
• Holds branches w/leaves up for sunlight
• Two types vascular tissue
– Xylem and phloem
– Also contain parenchyma cells and fibers
Plant Structure and Function
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Vascular Tissues
A. Tracheids, tangential section
• Xylem
– Carries water and
minerals from
roots to leaves
– Dead cells
Pits in
tracheid
• Perforated wall
• End-to-end
• Act like straws
B. Part of a vessel Pits
– Hollow with pores
or pits to allow
water movement
– Form woody parts
of plant
Vessel
members
Plant Structure and Function
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Vascular Tissues
• Phloem
– Carries P/S
products from
leaves to rest of
plant
– Also carries
hormones
– Living cells
• Sieve tube
members
– Plasmodesmata
(=gap junctions)
Plant Structure and Function
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Vascular Tissues
• Phloem
– Over time nucleus and other
organelles break down
– cytoplasm reduced to thin
layer lining inside of cell wall
– Sieve-tube members still live
several years
– In many angiosperms,
parenchyma cells connected
to mature sieve-tube
members assist with uptake
and unloading of sugars in
tissues that are growing or
storing food
Plant Structure and Function
10
Dermal Tissues
• Protect surface of
plants
• Epidermis covers plant
in continuous layer of
non-P/S cells
– May be single or
multiple layers
– Secrete waxy cuticle
• Protects against
desiccation and microbes
Plant Structure and Function
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Dermal Tissues
• Protect surface of
plants
• Stomata allow gas
exchange
– CO2 in, O2 and H2O
vapor out (at night O2 in
and CO2 out)
• Guard cells close over
stomata when water
levels get low due to
desiccation
Plant Structure and Function
12
Dermal Tissues
• Protect surface of
plants
• Trichomes are
outgrowths of
epidermis
– Root hairs
– Stinging nettles: inject
toxin into predators
– Hairy stems or leaves
Plant Structure and Function
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Vascular Tissue
Function
• Xylem carries water and
minerals up from roots
to rest of plant
• Phloem carries P/S
products from leaves to
rest of plant
Plant Structure and Function
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Vascular Tissue Function
• Xylem in center of trunk
• Phloem around outer
edges of trunk
Plant Structure and Function
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Xylem Function
Transpiration pulls
water out
Water molecules
adhere to each other
due to H-bonds
Roots actively pump
minerals in, water
follows via osmosis
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Phloem Function -- Translocation
1. High sugar in leaves is
actively pumped into
phloem, water follows
via osmosis from
xylem
2. High pressure at
source pushes sugar
solution towards root
3. Sugar actively pumped
into root, water leaves
via osmosis into xylem
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Growth
• Primary growth
– Growth in length or height
– Occurs at tips of branches and roots
• Secondary growth
– Growth in diameter
Plant Structure and Function
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Plant Growth
• Meristematic tissue
– Region of plant cell growth
– Undifferentiated, unspecialized
– Rapid rate of mitosis
– Area of cell division
• Cells will differentiate later
Plant Structure and Function
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Plant Growth
• Apical meristem
– Found at tips of stems
and roots
– Produces primary
growth
– Cells formed here are
primary tissues
• Will differentiate into
stems, leaves , flowers
later
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Growth
• Primary growth
– Growth occurs at
tip
– One cell pushed
forward, will
wear off
– One cell pushed
back, will
elongate causing
growth
– Will later
differentiate
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Growth
• Lateral meristem
– Occurs as a ring of cells inside stems and branches
– Vascular cambium
• Produces secondary growth
• Cells here differentiate as they are formed
– Xylem is pushed inside the ring and dies
» Form tree rings
– Phloem is pushed outside the ring
» Living cells that eventually die (bark) and wear away
» not permanent, no rings
Plant Structure and Function
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Secondary Growth
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Secondary Growth
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Secondary Growth
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Secondary Growth
• Secondary growth gives rise to tree rings
– One ring = one year in temperate regions
• Count rings to tell age of tree
– Rings wider when season is wet
• More water uptake expands cells further
• Width of rings tells about climate that year
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Secondary Growth
Plant Structure and Function
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Tree Rings
Plant Structure and Function
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Tree Rings
Plant Structure and Function
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Lost Colony of Roanoke
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• What is a hormone?
– Molecule that binds to receptor protein and
triggers reaction inside cell
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• What is a hormone?
– Molecule that binds to receptor protein and
triggers reaction inside cell
• Hormones have target cells
– Different target cells may respond differently to
same hormone
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Plants respond to hormones
– Start growing
– Stop growing
– Bends towards light
– Differentiation of specialized cell types
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Group of growth hormones
– Indoleacetic acid (IAA) most common
– Produced at stem tips, root tips, embryos, young
leaves, fruit
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Shoot growth (primary growth)
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Shoot growth (primary growth)
• Auxin produced in apical meristem and migrates to
zone of elongation
• Causes cells behind apical meristem to elongate
• Cut off stem tip
– no more auxin, no more primary growth
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Secondary growth
Plant Structure and Function; Illustrations
©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Secondary growth
• Auxin produced in apical meristem eventually migrates
to zone of differentiation
• Auxin stimulates differentiation of secondary xylem and
phloem
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Abscission
• Dropping of leaves & fruit
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Abscission
• Dropping of leaves & fruit
• Older leaf and fruit stems ↓ auxin production
– Cells at base of stem disintegrate
– Leaves or fruit fall off branch
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Phototropism
• Growing tips bend
towards light
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Phototropism
• Growing tips bend
towards light
• Auxin migrates away
from light
– Causes elongation
on “dark” side of
stem
– Stem bends toward
light
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Apical dominance
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Apical dominance
• Auxin from apical meristem inhibits side branches
– Pinch off apical meristem to get bushy plants
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Gravitropism
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Auxins
– Gravitropism
• Stems grow up
• Roots grow down
• Stems and roots
respond differently
to auxin
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Gibberellins
– Group of growth
hormones
– produced in stems,
young leaves, seeds
– Cell division and
elongation
• Stem elongation
• ↑ gibberellins gives
long, thin stems
w/few leaves
– Enhances auxins
• Fruit development
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Ethylene
– Ripens fruit
– Leaf abscission
– Fading of
chlorophyll
– Fading of flowers
• What do you do with an
avocado to ripen it
more quickly?
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Plant Hormones
• Ethylene
– Ripens fruit
– Leaf abscission
– Fading of
chlorophyll
– Fading of flowers
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Photoperiod
• Light helps regulate plant life cycle
– Most plants respond to amount of light/dark
– Flowering often triggered by photoperiod
• Short-day plants (actually long-night plants)
– Flower early spring or fall
• Long-day plants (actually short-night plants)
– Flower in summer
• Day –neutral plants respond to something other than
photoperiod
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Photoperiod
• Mechanism for flowering
– Actually respond to #dark hours
• Phytochrome is agent of flowering
– Two forms – Pfar-red and Pred
– Pred → Pfar-red in light
– Pfar-red → Pred slowly in dark
• Phytochrome far-red is active form
– Inhibits flowering in short day plants
– Stimulates flowering in long day plants
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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Photoperiod
Pfar-red inhibits flowers
Pfar-red stimulates flowers
Plant Structure and Function; Illustrations ©2010 Pearson Education, Inc.
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