Transcript Vascular cambium

+
Chapter 35:
Plant Structure,
Growth, and
Development
Mrs. Valdes
AP Biology
+ Developmental Plasticity

DEFINE: ability to alter itself in response to its environment

more marked in plants than animals

environment more greatly affects phenotype than genetic make-up
plant species by natural selection accumulate characteristics of
morphology that vary little within the species
TWO types
of leaves 

+ Concept 35.1: The plant body has a
hierarchy of organs, tissues, and cells


Plants have organs composed of
different tissues, composed of
cells
Three basic organs:
 Roots






Stems
Leaves
Basic morphology of vascular
plants reflect evolution as
organisms that draw nutrients
from below ground and to be
used above ground
Organs organized into root
system and shoot system
Roots rely on sugar produced by
photosynthesis in shoot system
Shoots rely on water and
minerals absorbed by root
system
Roots
+
• Roots: multicellular organs with
important functions:



•
•
•
•
Anchor plant
Absorb minerals and water
Store organic nutrients
Taproot system: consists of one
main vertical root that gives rise to
lateral roots, or branch roots
Adventitious roots: arise from
stems or leaves
Seedless vascular plants and
monocots:
• have fibrous root system
characterized by thin lateral roots
with no main root
Most plants absorption of water
and minerals occurs near root
hairs, where vast numbers of tiny
root hairs increase the surface area
+
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Prop Roots: Aid in support of tall,
top-heavy plants
Storage Roots: store food & water
in roots;
“Strangling” aerial roots: seeds
of strangler fig tree germinate in
branches of other trees, then send
lots of aerial roots around host tree
until it is totally shaded out and
dies
Buttress roots: Look like buttress
and support large trunk
Pneumatophores: “air roots”;
roots go above water to get oxygen
since oxygen is poor in muddy
mangrove waters
+ Stems
 Stem: organ
:


consisting of
alternating system of nodes, points
at which leaves are attached
Internodes: stem segments
between nodes
 Axillary
bud: structure
that has potential to form
a lateral shoot, or branch
 Apical bud: AKA
terminal bud; located
near shoot tip and causes
elongation of young shoot
 Apical dominance:
helps to maintain
dormancy in most
nonapical buds
+
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Rhizomes: horizontal shoot that
grows just below surface; vertical
shoots arise from axillary buds on
rhizome
Bulbs: vertical underground shoots
consisting of mostly enlarged bases
of leaves that store food
Stolons: horizontal shoots that grow
along surface; “runners” enable
plant to reproduce asexually
Tubers: enlarged ends of rhizomes
or stolons that specialize in storing
food
+ Leaves
 Leaf:
main photosynthetic
organ of most vascular
plants
 generally
consist of
flattened blade and stalk
called the petiole, which
joins leaf to node of stem
 Monocots
and eudicots
differ in arrangement of
veins, vascular tissue of
leaves


Most monocots have parallel veins
Most eudicots have branching veins
 In
classifying
angiosperms, taxonomists
may use leaf morphology
as criterion
+





Tendrils: usually modified leaves
but can be modified stems;
“lassoed” support anchors plant
and brings it closer to support
Spines: modified leaves;
photosynthesis carried out by
fleshy green part of cacti
Storage leaves: most succulents
modified to store water
Reproductive leaves: adventitious
plantlets can fall off and take root in
soil
Bracts: NOT petals but modified
leaves that surround a group of
flowers
Dermal, Vascular, and Ground Tissues
+
 Each
plant organ has dermal,
vascular, and ground tissues
 Tissue
system: functional unit
connecting all plant’s organs
 Dermal
tissue system: plants
outer protective covering
 Cuticle: waxy
coating helps
prevent water loss from epidermis
 Periderm: in woody plants,
protective tissues that replace
epidermis in older regions of
stems and roots
 Trichomes: outgrowths of shoot
epidermis; can help with insect
defense
 Vascular
tissue system:
+carries out long-distance
transport of materials
between roots and shoots
 two
vascular tissues :
 Xylem: conveys water and
dissolved minerals upward
from roots into the shoots

Phloem: transports organic
nutrients (FOOD) from where
they are made to where they are
needed
 Stele: vascular
or root
 In
tissue of stem
angiosperms stele of root is
a solid central vascular cylinder
 stele of stems and leaves
divided into vascular bundles,
strands of xylem and phloem
+
 Ground
tissue system:
tissues neither dermal
nor vascular
 includes
cells specialized
for storage,
photosynthesis, and
support
 Pith: ground
tissue
internal to vascular tissue
 Cortex: ground
tissue
external to vascular tissue
+Common Types of Plant Cells
 Plant
characterized by cellular differentiation,
the specialization of cells in structure and
function
 Plant
cell
types:

Parenchyma

Collenchyma

Sclerenchyma

Water-conducting
cells of the xylem

Sugar-conducting
cells of the phloem
•
+Parenchyma Cells
Mature parenchyma cells
–
Have thin and flexible primary walls
–
Lack secondary walls
–
Are least specialized
–
Perform most metabolic functions
–
Retain ability to divide and differentiate
+Collenchyma Cells
•
Collenchyma cells: grouped in strands; help
support young parts of plant shoot
•
•
•
have thicker and uneven cell walls
lack secondary walls
provide flexible support without restraining
growth
•
+ Sclerenchyma Cells
Sclerenchyma cells: rigid because of thick
secondary walls strengthened with lignin
•
•
dead at functional maturity
Two types:


Sclereids: short & irregular shape; thick lignified secondary walls
Fibers: long and slender; arranged in threads
+ Water Conducting Cells of Xylem
•
Two types of waterconducting cells:
BOTH DEAD at maturity
• Tracheids: found in
xylem of all vascular
plants
 Vessel elements:
common to most
angiosperms and few
gymnosperms
 align end to end to
form long micropipes
called vessels
•
+ Sugar-Conducting Cells of Phloem
•
•
Sieve-tube elements: alive at functional
maturity, though lack organelles
Sieve plates:
porous end walls
that allow fluid to
flow between cells
along sieve tube
•
Each sieve-tube
element has a
companion cell
whose nucleus and
ribosomes serve
both cells
Concept
35.2:
Meristems
generate
cells
+
for new organs
 Indeterminate
growth: plant growth
throughout its life
 Determinate growth: some plant organs
cease to grow at a certain size
 Annuals: complete life cycle in a year or less
 Biennials: require two growing seasons
 Perennials: live for many years
 Meristems: perpetually
+embryonic tissue; allow for
indeterminate growth
 Apical meristems: located at
tips of roots and shoots and at
axillary buds of shoots
 elongate
shoots and roots, AKA
primary growth
 Lateral
meristems: add
thickness to woody plants, AKA
secondary growth
 two
lateral meristems:
 vascular
cambium: adds
layers of vascular tissue
called secondary xylem
(wood) and secondary
phloem
 cork
cambium: replaces
epidermis with periderm,
which is thicker and tougher
Fig. 35-11
+
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
+ Meristems give rise
to:
initials: remain in
meristem,
 derivatives: become
specialized in
developing tissues

 In
woody plants,
primary and
secondary growth
occur
simultaneously but
in different
locations
+ Concept 35.3: Primary growth
lengthens roots and shoots
 Primary
plant body:
produced by primary
growth; parts of root
and shoot systems
produced by apical
meristems
 Root cap: covers root
tip; protects apical
meristem as root
pushes through soil
 Growth occurs just
behind the root tip, in
three zones of cells:



Zone of cell division
Zone of elongation
Zone of maturation
 Primary
growth of
+roots produces:
epidermis
 ground tissue
 vascular tissue

 In
most roots, stele
is vascular
cylinder
 Ground tissue fills
cortex (region
between vascular
cylinder and
epidermis)
 Endodermis:
innermost layer of
the cortex is called
Fig. 35-15-3
+
 Lateral
roots arise from within pericycle
 outermost
Emerging
lateral
root
cell layer in vascular cylinder
Epidermis
100 µm
Lateral root
Cortex
1
Vascular
cylinder
2
3
+ Primary Growth of Shoots
 Shoot
apical
meristem: domeshaped mass of
dividing cells at shoot
tip
 Leaves
develop from
leaf primordia along
sides of apical
meristem
 Axillary
buds develop
from meristematic cells
left at bases of leaf
primordia
Tissue
Organization
of
Stems
+
 Lateral
shoots develop from axillary
buds on stem’s surface
 In most eudicots, vascular tissue
consists of vascular bundles arranged
in ring
 In most monocot stems, the vascular
bundles scattered throughout the
ground tissue, rather than forming a
ring
Tissue Organization of Leaves
+
•
•
•
•
•
•
Epidermis in leaves
interrupted by stomata,
which allow CO2 exchange
between air and
photosynthetic cells in leaf
Each stomatal pore is flanked
by two guard cells, which
regulate its opening and closing
Mesophyll: ground tissue in a leaf; sandwiched between
the upper and lower epidermis
Spongy mesophyll: where gas exchange occurs; below
palisade mesophyll in upper part of leaf
vascular tissue of each leaf is continuous with vascular
tissue of the stem
Veins: leaf’s vascular bundles; function as leaf’s skeleton
•
Each vein enclosed by protective bundle sheath
Fig. 35-18
+
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)
Fig. 35-18a
+
Key
to labels
Dermal
Ground
Vascular
Cuticle
Sclerenchyma
fibers
Stoma
Upper
epidermis
Palisade
mesophyll
Spongy
mesophyll
Bundlesheath
cell
Lower
epidermis
Cuticle
Xylem
Vein
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Fig. 35-18b
+
Guard
cells
50 µm
Stomatal
pore
Epidermal
cell
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Fig. 35-18c
+
Key
to labels
Dermal
Ground
Upper
epidermis
Palisade
mesophyll
Vascular
100 µm
Spongy
mesophyll
Lower
epidermis
Vein Air spaces Guard cells
(c) Cross section of a lilac
(Syringa) leaf (LM)
Concept 35.4: Secondary growth adds
+
girth to stems and roots in woody plants
 Secondary
growth occurs in stems and roots of
woody plants but rarely in leaves
 Secondary plant body: tissues produced by
vascular cambium and cork cambium
 characteristic
of
gymnosperms and
many eudicots, but
NOT monocots
Fig. 35-19a1
+
(a) Primary and secondary growth
in a two-year-old stem
Epidermis
Cortex
Primary phloem
Vascular cambium
Primary xylem
Pith
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Fig. 35-19a2
+
(a) Primary and secondary growth
in a two-year-old stem
Epidermis
Cortex
Primary phloem
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular cambium
Primary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem
Fig. 35-19a3
+
(a) Primary and secondary growth
in a two-year-old stem
Epidermis
Cortex
Primary phloem
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular cambium
Primary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Periderm (mainly
cork cambia
and cork)
Most recent cork
cambium
Secondary phloem
Bark
Secondary
xylem
Cork
Layers of
periderm
Fig. 35-19b
+
Secondary xylem
Secondary phloem
Vascular cambium
Late wood
Early wood
Bark
Cork
cambium Periderm
0.5 mm
Cork
Vascular ray
0.5 mm
Growth ring
(b) Cross section of a three-yearold Tilia (linden) stem (LM)
+ Vascular Cambium and Secondary
Vascular Tissue
 Vascular
cambium: cylinder of meristematic
cells one cell layer thick
 develops
from undifferentiated parenchyma cells
 in cross section appears as a ring of initials
 initials increase vascular cambium’s
circumference and add secondary xylem to inside
and secondary phloem to outside
 Secondary
+of:
xylem accumulates as wood, and consists
 tracheids
 vessel
 fibers
 Early
elements (only in angiosperms)
wood: formed in spring, has thin cell walls to
maximize water delivery
 Late wood: formed in late summer, has thick-walled
cells and contributes more to stem support
 In temperate regions, vascular cambium of
perennials dormant through winter
 Tree rings visible where late and early wood meet;
can be used to estimate a tree’s age
 Dendrochronology: analysis
of tree ring growth patterns;
can be used to study past
climate change
 What does this graph
tell you?
 As
a tree or woody shrub ages, older layers of
+secondary xylem, AKA heartwood, no longer
transport water and minerals
 Outer layers, known as sapwood, still
transport materials through the xylem
 Older secondary
phloem sloughs
off and does not
accumulate
+ Cork Cambium and Production of
Periderm
 Cork
cambium: gives rise to secondary
plant body’s protective covering, or periderm
 Periderm
consists of cork cambium plus layers
of cork cells it produces
 Bark:
consists of all tissues external to
vascular cambium,
including secondary
phloem and periderm
 Lenticels: in periderm
allow for gas exchange
between living stem or
root cells and outside
air
Concept
35.5:
Growth,
morphogenesis,
and
+
differentiation produce the plant body
 Morphogenesis:
and organization
 Three
development of body form
developmental processes act in concert
to transform the fertilized egg into a plant:
 growth
 morphogenesis
 cellular
differentiation
Molecular
Techniques
Revolutionize
the
+
Study of Plants
 Arabidopsis:
model organism,
and first plant to
have its entire
genome
sequenced
 Studying
genes
and biochemical
pathways of
Arabidopsis
provide insights
into plant
development
Growth:
Cell
Division
and
Cell
Expansion
+
 By
increasing cell number, cell division in
meristems increases potential for growth
 Cell expansion accounts for actual increase in
plant size
 Plane (direction) and symmetry of cell division are
immensely important in determining plant form
 If planes of division
parallel to plane of
first division, single
file of cells is
produced
 If the planes of
division vary
randomly,
asymmetrical cell
division occurs
 Plane
in which cell divides determined during
+late interphase
 Microtubules
become
concentrated
into ring called
preprophase
band that
predicts future
plane of cell
division
+Orientation of Cell Expansion
 Plant
cells grow rapidly and “cheaply” by intake
and storage of water in vacuoles AKA “Water
Weight”
 Plant cells expand primarily along plant’s main
axis
 Cellulose microfibrils in cell wall restrict
direction of cell elongation
Morphogenesis and Pattern Formation
+
 Pattern
formation: development of
specific structures in specific
locations
 controlled
by homeotic genes
 determined by positional information
in form of signals indicating to each cell
its location
 may be provided by gradients of
molecules
 Polarity: having structural or
chemical differences at opposite ends
of organism, provides one type of
positional information
 Polarization initiated by asymmetrical
first division of plant zygote
 In gnom mutant of Arabidopsis,
establishment of polarity is
defective
Gene
Expression
and
Control
of
Cellular
+
Differentiation
 Cellular
differentiation depends on positional
information and is affected by homeotic genes
 Positional information underlies all processes
of development: growth, morphogenesis, and
differentiation
 Cells NOT dedicated
early to forming specific
tissues and organs
 Cell’s final position
 determines what kind
of cell it will become
Shifts in Development: Phase Changes
+
 Phase
changes:
developmental
phases from juvenile
phase to adult phase
 occur
within shoot
apical meristem
 Most
obvious
morphological
changes typically
occur in leaf size and
shape
Genetic Control of Flowering
+
 Flower
formation involves phase change from
vegetative growth to reproductive growth
 Triggered by combination of environmental cues
and internal signals
 Transition associated with switching on of floral
meristem identity genes
 Plant biologists identified
several organ identity genes
(plant homeotic genes) that
regulate development of
floral pattern
 Mutation in plant organ
identity gene  abnormal
floral development
 Researchers identified three classes of floral
+
organ identity genes
 ABC model of flower formation identifies how
floral organ identity genes direct formation of
four types of
floral organs
 Understanding
mutants of
organ identity
genes depict
how this model
accounts for
floral
phenotypes
Fig. 35-34a
+
Sepals
Petals
Stamens
A
B
(a) A schematic diagram of the ABC hypothesis
Carpels
C
A+B
gene
activity
B+C
gene
activity
C gene
activity
Carpel
Petal
A gene
activity
Stamen
Sepal
Fig. 35-34b
+
Active
genes:
BB
B B
AACCCC AA
BB
BB
CCCCCCCC
A ACCCC AA
AA
AA
ABBAABBA
Mutant lacking A
Mutant lacking B
Mutant lacking C
Whorls:
Carpel
Stamen
Petal
Sepal
Wild type
(b) Side view of flowers with organ identity mutations
+You should now be able to:
1.
Compare the following structures or cells:
–
–
–
–
–
2.
3.
4.
5.
6.
7.
Fibrous roots, taproots, root hairs, adventitious roots
Dermal, vascular, and ground tissues
Monocot leaves and eudicot leaves
Parenchyma, collenchyma, sclerenchyma, water-conducting cells of the
xylem, and sugar-conducting cells of the phloem
Sieve-tube element and companion cell
Explain the phenomenon of apical dominance
Distinguish between determinate and indeterminate
growth
Describe in detail the primary and secondary growth
of the tissues of roots and shoots
Describe the composition of wood and bark
Distinguish between morphogenesis, differentiation,
and growth
Explain how a vegetative shoot tip changes into a
floral meristem
+
2.
Explain the phenomenon of apical dominance
3.
Distinguish between determinate and
indeterminate growth
4.
Describe in detail the primary and secondary
growth of the tissues of roots and shoots
5.
Describe the composition of wood and bark
+
6.
Distinguish between morphogenesis,
differentiation, and growth
7.
Explain how a vegetative shoot tip changes
into a floral meristem