Download Plant Structure and Function Ch. 35

Plant Structure
and Function
Ch. 35
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Morphology of a Flowering Plant
• Root system and
shoot system are
connected by
vascular tissue that
is continuous
throughout plant
Monocots vs. Dicots
http://waynesword.palomar.edu/images/monocot3.gif
http://www.biology4kids.com/misc/photos
/dicotflower1.jpg
http://www.biologie.uni-hamburg.de/bonline/library/onlinebio/monocot_flower.gif
http://waynesword.palomar.edu/images/monocot3.gif
Plant Cell
Nucleus
Chloroplast
Cell Wall
Roots
• Functions
– Anchor plant in the soil
– Absorb water and
minerals
– Store food
Root Structure
Cortex
Vascular cylinder
Epidermis
Key
Root hair
Dermal
Zone of
maturation
Ground
Vascular
Zone of
elongation
Apical
meristem
Root cap
100 µm
Zone of cell
division
Root Systems
Taproot
Fibrous root
http://waynesword.palomar.edu/images/mangro3b.jpg
http://waynesword.palomar.edu/images/mangro3b.jpg
•Red mangrove growing in
seawater
•Adventitious prop roots support
and securely anchor this shrub
in the mud and loose sand of
tidal waters.
•Close-up view of prop roots
•Numerous pores called lenticels
which provide gas exchange
and an additional source of
oxygen for the submersed
roots.
Epidermis
Cortex
Vascular cylinder
-xylem
-phloem
Developing
lateral root
Buttress roots.
Aerial roots
Storage roots.
Prop root
Modified Roots
Stems
• Functions
– Support
– Transport
– Storage
Monocot arrangement
Dicot arrangement
• Proximity of terminal
bud inhibits growth of
axillary buds (Apical
dominance)
http://www.answers.com/topic/redtip9845-jpg-1
Modified Stems
Storage leaves
Stem
Roots
Stolons—allow asexual
reproduction
Bulbs—store food
Node
Rhizome
Root
Tubers—store food
Rhizomes—horizontal stem
Leaves
• Leaf structure
– Shape
– Size
– Edges
Mesophyll
Leaf Structure
Stomata
Modified Leaves
• Tendrils—allow plant
to cling to support
• Spines—reduces water
loss
Modified Leaves
• Storage—modified for
water storage
(succulents)
• Bracts—attracts
pollinators
Modified Leaves
• Reproductive leaves—
produce adventitious
plantlets which fall off
and take root
Tissue Systems
1. Ground System
•Parenchyma --cube-shaped, thin and flexible cell walls
--function in photosynthesizing and
storing organic products and wound
healing
•Collenchyma --elongated, thicker cell walls
--cells grouped in strands or cylinders
to support leaves and stems (parts
that are still growing)
•Sclerenchyma--cells have rigid, thick walls with lignin
--at maturity, consists of dead cells
--supports and strengthens plant
Tissue Systems
2. Vascular System
Xylem -Conducts water and minerals
from roots to plant
-composed of dead cells that
form water-pipe system
Phloem -Conducts food throughout
plant
-composed of living cells
arranged into tubules
Water-conducting Cells of Xylem
WATER-CONDUCTING CELLS OF THE XYLEM
Vessel
Tracheids
100 µm
60 µm
ma cells
Pits
Tracheids and vessels
(colorized SEM)
Vessel
element
Vessel elements with
perforated end walls
Tracheids
Vessel elements with
perforated end walls
Sugar-conducting Cells of Phloem
Tracheids
SUGAR-CONDUCTING CELLS OF THE PHLOEM
x of Sambucus,
ed red) (LM)
Sieve-tube members:
longitudinal view
(LM)
Companion
cell
lls in pear (LM)
Sieve-tube
member
Plasmodesma
25 µm
Sieve
plate
Nucleus
Cytoplasm
Companion
cell
30 µm
15 µm
from ash tree) (LM)
Sieve-tube members:
longitudinal view
Sieve plate with pores (LM)
Sheath of sclerenchyma
phloem
xylem
parenchyma
Tissue Systems
3. Dermal Tissue System
- Forms the outer covering of
plants
•Epidermis-outer layer of cells
covered by waxy cuticle
•Stomata-structures that regulate
passage of gases into/out of plant
Meristems: Primary Growth
Growing region where cells actively divide
Apical meristems- grow in length at tips of
stems and roots
Primary growth in stems
Shoot apical
meristems
(in buds)
Epidermis
Cortex
Primary phloem
Primary xylem
Vascular
cambium
Cork
cambium
Lateral
meristems
Pith
Secondary growth in stems
Periderm
Cork
cambium
Pith
Cortex
Primary
phloem
Primary
xylem
Root apical
meristems
Secondary
xylem
Secondary
phloem
Vascular cambium
Lateral meristems
• Add thickness to woody
plants, a process called
secondary growth
• Two lateral meristems
– vascular cambium
adds layers of vascular
tissue called secondary
xylem (wood) and
secondary phloem
– cork cambium
replaces the epidermis
with periderm, which
is thicker and tougher
Primary Growth in Roots
Cortex
Vascular cylinder
Epidermis
Key
Root hair
Dermal
Zone of
maturation
Ground
Vascular
Zone of
elongation
Apical
meristem
Root cap
100 µm
Zone of cell
division
Primary Growth in Shoots
Apical meristem
Leaf primordia
Developing
vascular
strand
Axillary bud
meristems
0.25 mm
•Secondary
growth occurs in
stems and roots
of woody plants
but rarely in
leaves
Vascular cambium
•Produces
secondary xylem
and phloem
Cork cambium
•Produces tough,
thick covering for
stems and roots
•Replaces
epidermis
Anatomy of a Tree Trunk
• As a tree or woody
shrub ages, the older
layers of secondary
xylem, the heartwood,
no longer transport
water and minerals
• The outer layers,
known as sapwood,
still transport materials
through the xylem
Growth ring
Vascular
ray
Heartwood
Secondary
xylem
Sapwood
Vascular cambium
Secondary phloem
Bark
Layers of periderm
Growth, morphogenesis, and
differentiation produce the plant body
• The three developmental processes of growth,
morphogenesis, and cellular differentiation act in
concert to transform the fertilized egg into a
plant
Growth: Cell Division and Cell
Expansion
• By increasing cell number, cell division in
meristems increases the potential for growth
• Cell expansion accounts for the actual
increase in plant size
The Plane and Symmetry of Cell
Division
• The plane (direction) and symmetry of cell
division are immensely important in determining
plant form
• If the planes of division are parallel to the plane of
the first division, a single file of cells is produced
Division in
same plane
Single file of cells forms
Plane of
cell division
Division in
three planes
Cube forms
Nucleus
Cell divisions in the same plane produce a single file of cells, whereas cell divisions in three planes give rise to a cube.
The Plane and Symmetry of Cell
Division
• If the planes of division vary randomly,
asymmetrical cell division occurs
Developing
guard cells
Asymmetrical
cell division
Unspecialized
epidermal cell
Unspecialized Guard cell
epidermal cell “mother cell”
Unspecialized
epidermal cell
An asymmetrical cell division precedes the development of epidermal guard cells, the cells that border stomata (see Figure 35.17).
The Plane and Symmetry of Cell
Division
• The plane in which a
cell divides is
determined during late
interphase
• Microtubules become
concentrated into a
ring called the
preprophase band
Preprophase bands
of microtubules
Nuclei
Cell plates
10 µm
Genetic Control of Flowering
• Flower formation involves a phase change from
vegetative growth to reproductive growth
• It is triggered by a combination of environmental
cues and internal signals
• Transition from vegetative growth to flowering
is associated with the switching-on of floral
meristem identity genes
• Plant biologists
have identified
several organ
identity genes that
regulate the
development of
floral pattern
Pe
Ca
St
Se
Pe
Se
Normal Arabidopsis flower. Arabidopsis
normally has four whorls of flower parts: sepals
(Se), petals (Pe), stamens (St), and carpels (Ca).
Pe
Pe
Se
Abnormal Arabidopsis flower. This flower has
an extra set of petals in place of stamens and
an internal flower where normal plants have
carpels.
• The ABC model of flower formation identifies
how floral organ identity genes direct the
formation of the four types of floral organs
Sepals
Petals
Stamens
A
B
Carpels
C
B+C
A+B
gene
gene
activity
activity
A gene
activity
A schematic diagram of the ABC
hypothesis
C gene
activity