Download Chapter 24 Plant Structure

Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 24
Flowering Plants:
Structure and
Organization
Lecture Outline
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Outline
• 24.1 Organs of Flowering Plants
• 24.2 Tissues of Flowering Plants
• 24.3 Organization and Diversity of Roots
• 24.4 Organization and Diversity of Stems
• 24.5 Organization and Diversity of Leaves
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24.1 Organs of Flowering Plants
• Flowering plants, or angiosperms, are extremely diverse
but share many common structural features.
• Most flowering plants possess a root system and a shoot
system
 The root system simply consists of the roots,
 The shoot system consists of the stem and leaves.
• A typical plant features three vegetative organs
 roots, stems, and leaves
 Vegetative organs are concerned with growth and
nutrition.
• Flowers, seeds, and fruits are structures involved in
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reproduction.
Organization of Plant Body
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terminal bud
blade
leaf
vein
petiole
axillary bud
stem
node
internode
node
vascular tissues
shoot system
root system
branch
root
root hairs
primary
root
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Organs of Flowering Plants
• Roots
 Generally, the root system is at least equivalent in
size and extent to the shoot system
• Anchors plant in soil
• Absorbs water and minerals from the soil
• Produces hormones
 Root hairs:
• Projections from epidermal root-hair cells
• Greatly increase absorptive capacity of root
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Organs of Flowering Plants
• Stems
 Shoot system of a plant is composed of the
stem, branches, and leaves
• Stem is the main axis of a plant that elongates and
produces leaves
– Nodes occur where leaves are attached to the stem
– Internode is region between nodes
– Axillary buds can produce new branches of the stem (or
flowers)
• Stem also has vascular tissue that transports water
and minerals
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Organs of Flowering Plants
• Leaves
 major part of the plant that carries on
photosynthesis
• Foliage leaves are usually broad and thin
– Blade - Wide portion of foliage leaf
– Petiole - Stalk attaching blade to stem
– Leaf Axil - Upper acute angle between petiole and stem
where the axillary bud is found
• Tendrils - Leaves that attach to objects
• Bulbs - Leaves that store food
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Vegetative Organs of Several
Eudicots
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blade
petiole
stems
stem
roots
lateral root
a. Root system, dandelion
b. Shoot system, bean seedling
c. Leaves, pumpkin seedling
a: © Dorling Kindersley/Getty Images; b:© Dwight Kuhn; c: © Dwight Kuhn
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Organs of Flowering Plants
• Monocots (Single cotyledon)
 Cotyledons act as transfer tissue
• Nutrients are derived from the endosperm
 Root vascular tissue occurs in ring
 Parallel leaf venation
 Flower parts arranged in multiples of three
• Eudicots (Two cotyledons)




Cotyledons supply nutrients to seedlings
Root phloem located between xylem arms
Netted leaf venation
Flower parts arranged in multiples of four or
five
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Flowering Plants are Either
Monocots or Eudicots
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Root
Stem
Leaf
Vascular bundles
scattered in stem
Leaf veins form
a parallel pattern
Flower
Monocots
Seed
Root xylem and
phloem in a ring
Flower parts in threes
and multiples of three
Eudicots
One cotyledon in seed
Two cotyledons in seed
Root phloem between
arms of xylem
Vascular bundles
in a distinct ring
Leaf veins form
a net pattern
Flower parts in fours or
fives and their multiples
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24.2 Tissues of Flowering
Plants
• Meristematic tissue enables flowering
plants to grow throughout their lifetime
• Apical meristems at the tips of stems and
roots increase the length of these tissues
• Apical meristem produces three types of
meristem, which produce three
specialized tissues
 Epidermal tissue
 Ground tissue
 Vascular tissue
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Tissues of Flowering Plants
• Epidermal Tissue
 Forms the outer protective covering of a plant
 Epidermis contains closely packed epidermal cells
• Epidermal cells exposed to air are covered with
waxy cuticle
• Root epidermal cells have root hairs
• Epidermal cells of stems, leaves, and reproductive
organs have trichomes
• Lower leaf surface contains stomata
 In older woody plants, the epidermis of the stem is
replaced by periderm
• Major component is cork
• New cork is made by cork cambium
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Modifications of Epidermal Tissue
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corn seedling
guard cell
chloroplasts
periderm
lenticel
cork cambium
cork
root hairs
enlongating
root tip
a. Root hairs
Stoma
b. Stoma of leaf
nucleus
c. Cork of older stem
a: © Evelyn Jo Johnson; b: © J.R. Waaland/Biological Photo Service; c: © Kingsley Stern
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Tissues of Flowering Plants
• Ground tissue forms bulk of a flowering plant
 Parenchyma cells:
• Least specialized and are found in all organs of plant
• Can divide and give rise to more specialized cells
 Collenchyma cells:
• Have thicker primary walls
• Form bundles underneath epidermis
• Provide flexible support for immature regions of the plant
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Tissues of Flowering Plants
 Ground tissue (continued)
• Sclerenchyma cells:
– Have thick secondary walls impregnated with
lignin
– Most are nonliving
– Primary function is to support mature regions of
the plant
– Two types of sclerenchyma cells
» Fibers
» Sclereids
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Ground Tissue Cells
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a. Parenchyma cells
50 mm
50 mm
50 mm
b. Collenchyma cells
c. Sclerenchyma cells
(All): © Biophoto Associates/Photo Researchers, Inc.
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Tissues of Flowering Plants
• Vascular Tissue
 Xylem transports water and minerals from the
roots to the leaves
• Tracheids
– Long, with tapered ends
– Water moves across pits in end walls and side
walls
– Vascular rays between rows of tracheids
conduct water across the width of the plant
• Vessel Elements
– Larger, with perforated plates in their end walls
– Form a continuous vessel for water and mineral
transport
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Xylem Structure
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vessel
element
tracheids
xylem
parenchyma
cell
vessel
element
tracheid
perforation
plate
pitted
walls
pits
50 mm
a. Xylem micrograph (left) and drawing (to side)
b. T wo types of vessels
c. Tracheids
a: © J. Robert Waaland/Biological Photo Service
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Tissues of Flowering Plants
• Vascular Tissue
 Phloem transports sucrose and other organic
compounds from the leaves to the roots
• Sieve-tube members function as conducting cells
– Contain cytoplasm, but lack nuclei
– Sieve plate – cluster of pores in wall
• Each sieve-tube member has a companion cell
– Plasmodesmata connect the two
– Companion cell contains a nucleus
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Phloem Structure
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sieve plate
sieve-tube
member
sieve-tube member
companion cell
companion
cell
sieve plate
nucleus
phloem
parenchyma
cells
20 mm
a. Phloem micrograph (left) and drawing (to side)
b. Sieve-tube member and companion cells
a: © George Wilder/Visuals Unlimited
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24.3 Organization and Diversity
of Roots
• Root cap contains root apical meristem
• Zone of cell division contains primary meristems
• Zone of elongation contains cells that are
lengthening and becoming specialized
• Zone of maturation contains fully differentiated
cells
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Organization and Diversity of
Roots
• Tissues of a Eudicot Root:
 Epidermis - outer layer of root
 Cortex – composed of parenchyma cells
allowing water and minerals movement
 Endodermis – forms a boundary between
cortex and inner vascular cylinder
• Casparian strip
 Vascular Tissue - contains xylem and
phloem
• Pericycle – mitotically active and can begin
development of branch or lateral roots
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Eudicot Roots
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Vascular
cylinder
endodermis
pericycle
phloem
xylem
cortex
epidermis
root hair
50 µm
b. Vascular cylinder
phloem
endodermis
Zone of
maturation
water and
minerals
Casparian
strip
xylem of
vascular
cylinder
pericycle
Zone of
elongation
c. Casparian strip
procambium
Zone of
cell division
ground
meristem
protoderm
root apical meristem
protected by
root cap
root cap
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a. Root tip
a: Courtesy Ray F. Evert/University of Wisconsin Madison; b: © CABISCO/Phototake
Branching of Eudicot Root
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epidermis
emerging
branch root
cortex
pericycle
vascular
cylinder
endodermis
© Dwight Kuhn; 24.10a: © John D. Cunningham/Visuals Unlimited
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Organization and Diversity of
Roots
• Monocot roots:
 Ground tissue of root’s pith is surrounded by
vascular ring
 Have the same growth zones as eudicot roots,
but do not undergo secondary growth
 Have pericycle, endodermis, cortex, and
epidermis
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Monocot Root
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vascular
cylinder
a.
pith
phloem
xylem
pericycle
endodermis
cortex
epidermis
b.
100 mm
a: © John D. Cunningham/Visuals Unlimited; b: Courtesy George Ellmore, Tufts University
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Organization and Diversity of
Roots
• Primary root (taproot) - Fleshy, long single
root, that grows straight down
 Stores food
• Fibrous root system - Slender roots and lateral
branches
 Anchors plant to soil
• Adventitious roots - Roots develop from organs
of the shoot system instead of the root system
 Prop roots
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Organization and Diversity of
Roots
• Haustoria:
 Found in parasitic plants
 Rootlike projections that grow into host plant
 Make contact with vascular tissue of the host plant
and extract water and nutrients
• Mycorrhizae:
 Mutualistic associations between roots and fungi
 Assist in water and mineral extraction
• Root nodules
 Contain nitrogen-fixing bacteria
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Root Diversity
a. Taproot
c. Prop roots ,a type of
adventitious root
b. Fibrous root system
d. Pneumatophores of black
mangrove trees
e. Aerial roots of English ivy clinging to tree trunks
(a): © Dr. Robert Calentine/Visuals Unlimited; (b): © Evelyn Jo Johnson; (c): © David Newman/Visuals Unlimited; (d): © Alan and Linda Detrick/Photo Researchers, Inc.;
(e) left: © David Sieren/Visuals Unlimited; (e) right: © Professor David F. Cox, Lincoln Land Community College
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24.4 Organization and Diversity
of Stems
• Shoot apical meristem
 Produces new cells that elongate and
increase stem length
 Protected by terminal bud
• Enveloped by leaf primordia
• Specialized primary meristems
– Protoderm – gives rise to the epidermis
– Ground Meristem – gives rise to pith and cortex
– Procambium – produces primary xylem and
phloem
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Woody Twig
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
bud scale
one year's
growth
lenticel
terminal bud
internode
node
node
terminal bud
scale scars
axillary bud
stem
leaf scar
bundle scars
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Shoot Tip and Primary Meristems
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Three Primary Meristems:
protoderm
leaf primordium
shoot apical
meristem
protoderm
ground
meristem
procambium
ground
meristem
procambium
Primary Tissues
internode
epidermis
axillary bud
pith
cortex
vascular
cambium
vascular bundles
pith
primary xylem
vascular cambium
primary phloem
cortex
primary
xylem
primary
phloem
a. Shoot tip
b. Fate of primary meristems
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Organization and Diversity of
Stems
• Herbaceous Stems
 Mature non-woody stems exhibit only primary
growth
• Outermost tissue covered with waxy cuticle
• Stems have distinctive vascular bundles
– Herbaceous eudicots - Vascular bundles arranged in
distinct ring
– Monocots - Vascular bundles scattered throughout stem
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Herbaceous Eudicot Stem
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epidermis
phloem fiber
xylem
phloem
cortex
epidermis
pith
vascular
bundle
100 µm
pith
vascular cambium
50 µm
parenchyma
collenchyma
Left: © Ed Reschke; Right: Courtesy Ray F. Evert/University of Wisconsin Madison
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Monocot Stem
epidermis
ground tissue
vascular
bundle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ground tissue
(parenchyma)
xylem
phloem
bundle sheath cells
(Top): © CABISCO/Phototake; (Bottom): © Kingsley Stern
vessel element
air space
sieve-tube member
companion cell
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Organization and Diversity of
Stems
• Woody Stems
 Woody plants have both primary and
secondary tissues
• Primary tissues formed each year from primary
meristems
• Secondary tissues develop during first and
subsequent years from lateral meristems
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Organization and Diversity of
Stems
• Woody stems have both primary and secondary
growth
 Primary growth increases the length of the plant
 Secondary growth increases the girth
• Woody stems have no vascular tissue, and
instead have three distinct regions
 Bark
 Wood
 Pith
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Secondary Growth of Stems
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Vascular cambium:
Lateral meristem that will
produce secondary xylem
and secondary phloem in
each succeeding year.
pith
primary xylem
primary phloem
a.
b.
Periderm: As a stem
becomes woody, epidermis
is replaced by the periderm.
cortex
epidermis
pith
primary xylem
secondary xylem
vascular cambium
secondary phloem
lenticel
primary phloem
cortex
cork cambium
cork
Bark: Includes periderm and also
living secondary phloem.
Wood: Increases each
year; includes annual
rings of xylem.
c.
xylem ray
phloem ray
secondary xylem
vascular cambium
secondary phloem
cork cambium
cork
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Organization and Diversity of
Stems
• Bark
 Bark of a tree contains cork, cork cambium, and
phloem
 Bark can be removed, but it is harmful to the plant
due to lack of organic nutrient transport
 Cork cells are impregnated with suberin
• Gas exchange is impeded except at lenticels
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Organization and Diversity of
Stems
• Wood
 Wood is secondary xylem that builds up year after year
• Vascular cambium is dormant during winter
• Annual ring is made up of spring wood and summer
wood
 In older trees, inner annual rings, called heartwood, no
longer function in water transport
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Three-year-old Woody Twig
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cork
cork cambium
cortex
phloem ray
Bark
phloem
Vascular Cambium
summer
wood
spring
wood
secondary
xylem
annual
ring
Wood
primary xylem
Pith
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© Ed Reschke/Peter Arnold, Inc.
Tree Trunk
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
annual rings
heart wood
sap wood
vascular
cambium
phloem
cork
a. Tree trunk,
cross-sectional view
b. Tree trunk,
longitudinal view
a: © Ardea London Limited
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Organization and Diversity of
Stems
• Stem Diversity
 Above ground vertical stems
 Stolons
• Above ground horizontal stems
• Produce new plants when nodes touch the ground
 Rhizomes
• Underground horizontal stems
• Contribute to asexual reproduction
• Variations:
– Tubers - Enlarged portions functioning in food storage
– Corms - Underground stems that produce new plants during
the next season
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Stem Diversity
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
rhizome
branch
papery
leaves
axillary
bud
adventitious roots
stolon
corm
axillary
bud
node
rhizome
adventitious
roots
tuber
adventitious roots
a. Stolon
b. Rhizome
c. Tuber
d. Corm
a: © The McGraw-Hill Companies Inc./Evelyn Jo Johnson, photographer; b: © Science Pictures Limited/Photo Researchers, Inc.;
c: © The McGraw Hill Companies, Inc./Carlyn Iverson, photographer; d: © The McGraw Hill Companies, Inc./Carlyn Iverson, photographer
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24.5 Organization and Diversity
of Leaves
• Leaves contain:
 Upper and lower epidermis
• Waxy cuticle
• Trichomes
• Lower epidermis has stomata for gas exchange
 Mesophyll
• Eudicot leaves have
– Palisade mesophyll containing elongated cells
– Spongy mesophyll containing irregular cells bounded by air
spaces
• Contains many chloroplasts
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Leaf Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
trichomes
cuticle
Water and minerals
enter leaf through xylem.
upper epidermis
palisade
mesophyll
Sugar exits leaf
through phloem.
air space
bundle sheath cell
spongy
mesophyll
lower epidermis
cuticle
leaf vein
stoma
chloroplast
central vacuole
epidermal cell
upper
epidermis
nucleus
chloroplast
palisade
mesophyll
O2 and H2O
exit leaf
through stoma.
nucleus
leaf vein
guard cell
CO2 enters leaf
through stoma.
mitochondrion
spongy
mesophyll
stoma
Leaf cell
Stoma and guard cells
lower
epidermis
100 m
SEM of leaf cross section
© Jeremy Burgess/SPL/Photo Researchers, Inc.
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Organization and Diversity of
Leaves
• Leaf Diversity
 Blade of a leaf can be simple or compound
 Leaves are adapted to environmental conditions
• Shade leaves
• Spines
• Climbing leaves
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Classification of Leaves
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axillary bud
Alternate leaves,
beech
Simple leaf, magnolia
axillary buds
Palmately compound leaf,
buckeye
Whorled leaves,
bedstraw
Pinnately compound leaf
black walnut,
a. Simple versus compound leaves
Opposite leaves, maple
b. Arrangement of leaves on stem
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Leaf Diversity
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
stem
spine
tendril
hinged
leaves
a. Cactus, Opuntia
b. Cucumber, Cucumis
c. Venuss
’ flytrap, Dionaea
a: © Patti Murray Animals Animals/Earth Scenes; b: © Gerald & Buff Corsi/Visuals Unlimited; c: © P. Goetgheluck/Peter Arnold, Inc.
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