Transcript Plants

Plants
The Important parts.
Basic Vocab you need to know!
• seed - an embryo and nutrients surrounded by a
protective coat
• Megasporangia produce megaspores that give
rise to female gametophytes
• Microsporangia produce microspores that give
rise to male gametophytes and develop into
pollen
Common in all seed plants
– Reduced gametophytes
– Heterospory = magasporangia make female
gametophytes and microsporangia make male
gametophytes
– Ovules
– Pollen
• Seeds provide some evolutionary advantages
over spores:
– They may remain dormant for days to years, until
conditions are favorable for germination
– They may be transported long distances by wind or
animals
• Pollination is the transfer of pollen to
the part of a seed plant containing the
ovules
• In what ways could pollen be
dispersed?
Fig. 30-3-2
Female
gametophyte (n)
Spore wall
Egg nucleus (n)
Male gametophyte
(within a germinated
pollen grain) (n)
Micropyle
(b) Fertilized ovule
Discharged
sperm nucleus (n)
Pollen grain (n)
• A flower is a
specialized shoot
with up to four
types of modified
leaves:
Flowers
– Sepals, which
enclose the flower
– Petals, which are
brightly colored and
attract pollinators
– Stamens, which
produce pollen on
their terminal anthers
– Carpels, which
produce ovules
•A carpel consists of an
ovary at the base and
a style leading up to a
stigma, where pollen
is received
Fig. 30-7
Stigma
Stamen
Anther
Carpel
Style
Filament
Ovary
Petal
Sepal
Draw and label this in your
notes! You will need to
know this!
Ovule
Fruit AKA Ovaries
• A fruit typically consists of a mature
ovary but can also include other flower
parts
• Fruits protect seeds and aid in their
dispersal
Fig. 30-8
Tomato
Ruby grapefruit
Nectarine
What are
the various
methods in
which seeds
can be
dispersed?
Hazelnut
Milkweed
Fig. 30-9
Wings
Seeds within berries
Barbs
Angiosperm Diversity
• Cotyledon - seed leaves (found within a seed,
the embryo consists of a root and two
cotyledons)
• The two main groups of angiosperms are
monocots (one cotyledon) and eudicots
(“true” dicots) AKA dicots
• The clade eudicot includes some groups
formerly assigned to the paraphyletic dicot
(two cotyledons) group
Fig. 30-13n
Monocot
Characteristics
You will
need to
know these
characteristi
cs from this
and the next
slide!
Eudicot
Characteristics
Embryos
Two cotyledons
One cotyledon
Leaf
venation
Veins usually
parallel
Veins usually
netlike
Stems
Vascular tissue
scattered
Vascular tissue
usually arranged
in ring
Fig. 30-13o
Monocot
Characteristics
Eudicot
Characteristics
Roots
Taproot (main root)
usually present
Root system
usually fibrous
(no main root)
Pollen
Pollen grain with
one opening
Pollen grain with
three openings
Flowers
Floral organs
usually in
multiples of three
Floral organs usually
in multiples of
four or five
Systems
• Roots are multicellular organs with
important functions:
– Anchoring the plant
– Absorbing minerals and water
– Storing organic nutrients
• taproot system consists of one main
vertical root that gives rise to lateral
roots, or branch roots
Fig. 35-4
Prop roots
“Strangling”
aerial roots
Storage roots
Buttress roots
Pneumatophores
• A stem is an organ consisting of
– An alternating system of nodes, the points at which
leaves are attached
– Internodes, the stem segments between nodes
• An axillary bud is a structure that has the
potential to form a lateral shoot, or branch
• An apical bud, or terminal bud, is located
near the shoot tip and causes elongation of a
young shoot
• Apical dominance helps to maintain
dormancy in most nonapical buds
Fig. 35-2
Reproductive shoot (flower)
Apical bud
Node
Internode
Apical
bud
Vegetative
shoot
Leaf
Shoot
system
Blade
Petiole
Axillary
bud
Stem
Taproot
Lateral
branch
roots
Root
system
• The leaf is the main photosynthetic
organ of most vascular plants
• Leaves generally consist of a flattened
blade and a stalk called the petiole,
which joins the leaf to a node of the
stem
• Monocots and eudicots differ in the
arrangement of veins, the vascular
tissue of leaves
– Most monocots have parallel veins
– Most eudicots have branching veins
Fig. 35-6
(a) Simple leaf
Petiole
Axillary bud
Leaflet
(b) Compound
leaf
Petiole
Axillary bud
(c) Doubly
compound
leaf
Leaflet
Petiole
Axillary bud
• Lateral meristems add thickness to
woody plants, a process called
secondary growth
• There are two lateral meristems: the
vascular cambium and the cork cambium
• The vascular cambium adds layers of
vascular tissue called secondary xylem
(wood) and secondary phloem
• The cork cambium replaces the
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
Primary Growth of Roots
• The root tip is covered by a root cap,
which protects the apical meristem as the
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
Video: Root Growth in a Radish Seed (Time Lapse)
Fig. 35-13
Cortex
Vascular cylinder
Epidermis
Key
to labels
Dermal
Root hair
Zone of
differentiation
Ground
Vascular
Zone of
elongation
Apical
meristem
Root cap
100 µm
Zone of cell
division
Fig. 35-14a2
(a) Root with xylem and phloem in the center
(typical of eudicots)
Endodermis
Key
to labels
Pericycle
Dermal
Ground
Vascular
Xylem
Phloem
50 µm
Fig. 35-14b
Epidermis
Cortex
Endodermis
Key
to labels
Vascular
cylinder
Pericycle
Dermal
Ground
Vascular
Core of
parenchyma
cells
Xylem
Phloem
100 µm
(b) Root with parenchyma in the center (typical of
monocots)
Response in Plants
Water Pressure and Osmosis
• Water potential is a measurement that
combines the effects of solute
concentration and pressure
• Water potential determines the direction
of movement of water
• Water flows from regions of higher water
potential to regions of lower water
potential – this sounds familiar!!!
OSMOSIS!!!!
• Water potential is abbreviated as Ψ and
measured in units of pressure called
megapascals (MPa)
• Ψ = 0 MPa for pure water at sea level
and room temperature
• Turgor pressure is the pressure
exerted by the plasma membrane
against the cell wall, and the cell wall
against the protoplast – Look up what
this is right now! – What is it?
• Water and minerals can travel through a
plant by three routes:
– Transmembrane route: out of one cell, across
a cell wall, and into another cell
– Symplastic route: via the continuum of cytosol
– Apoplastic route: via the cell walls and
extracellular spaces
Mechanisms of Stomatal
Opening and Closing
• Changes in turgor pressure open and
close stomata
• These result primarily from the reversible
uptake and loss of potassium ions by the
guard cells
Fig. 36-17
Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Vacuole
Guard cell
(a) Changes in guard cell shape and stomatal opening and
closing (surface view)
Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
H2O
H2O
H2O
H2O
H2O
K+
H2O
H2O
H2O
H2O
H2O
(b) Role of potassium in stomatal opening and closing
Fig. 36-17a
Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Vacuole
Guard cell
(a) Changes in guard cell shape and stomatal opening and
closing (surface view)
Fig. 36-17b
Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed
H 2O
H2O
H 2O
H 2O
H 2O
K+
H 2O
H 2O
H 2O
H 2O
(b) Role of potassium in stomatal opening and closing
H2O
Stimuli for Stomatal Opening and
Closing
• Generally, stomata open during the day
and close at night to minimize water loss
• Stomatal opening at dawn is triggered by
light, CO2 depletion, and an internal
“clock” in guard cells
• All eukaryotic organisms have internal
clocks; circadian rhythms are 24-hour
cycles
Bulk Flow by Positive Pressure:
The Mechanism of Translocation
in
Angiosperms
• In studying angiosperms, researchers
have concluded that sap moves through
a sieve tube by bulk flow driven by
positive pressure
Animation: Translocation of Phloem Sap in Summer
Animation: Translocation of Phloem Sap in Spring
Fig. 36-20
Vessel
(xylem)
Sieve tube Source cell
(phloem) (leaf)
H2O
1 Loading of sugar
Sucrose
1
H2O
Bulk flow by negative pressure
Bulk flow by positive pressure
2
2 Uptake of water
3 Unloading of sugar
Sink cell
(storage
root)
4 Water recycled
3
4
H2O
Sucrose
Concept 39.2: Plant hormones
help coordinate growth,
development, and responses to
stimuli
• Hormones are chemical signals that
coordinate different parts of an organism
The Discovery of Plant
Hormones
• Any response resulting in curvature of
organs toward or away from a stimulus is
called a tropism
• Tropisms are often caused by hormones
• Phototropism – plant’s response to
light
Video: Phototropism
Fig. 39-5b
RESULTS
Darwin and Darwin: phototropic response
only when tip is illuminated
Light
Tip
removed
Tip covered
by opaque
cap
Tip
covered
by transparent
cap
Site of
curvature
covered by
opaque
shield
• The term auxin refers to any chemical
that promotes elongation of coleoptiles
• Auxin is involved in root formation and
branching
• Auxin affects secondary growth by
inducing cell division in the vascular
cambium and influencing differentiation
of secondary xylem
• Cytokinins are so named because they
stimulate cytokinesis (cell division)
Control of Cell Division and Differentiation
• Cytokinins are produced in actively growing
tissues such as roots, embryos, and fruits
• Cytokinins work together with auxin to control
cell division and differentiation
Control of Apical Dominance
• Cytokinins, auxin, and other factors
interact in the control of apical
dominance, a terminal bud’s ability to
suppress development of axillary buds
• If the terminal bud is removed, plants
become bushier
Fig. 39-9
Lateral branches
“Stump” after
removal of
apical bud
(b) Apical bud removed
Axillary buds
(a) Apical bud intact (not shown in photo)
(c) Auxin added to decapitated stem
• Gibberellins have a variety of effects,
such as stem elongation, fruit growth,
and seed germination
Stem Elongation
• Gibberellins stimulate growth of leaves
and stems
• In stems, they stimulate cell elongation
and cell division
Fruit Growth
• In many plants, both auxin and
gibberellins must be present for fruit to
set
• Gibberellins are used in spraying of
Thompson seedless grapes
Fig. 39-10
(b) Gibberellin-induced fruit
growth
(a) Gibberellin-induced stem
growth
Germination
• After water is imbibed, release of
gibberellins from the embryo signals
seeds to germinate
Fig. 39-11
1 Gibberellins (GA)
2 Aleurone secretes
send signal to
aleurone.
-amylase and other enzymes.
3 Sugars and other
nutrients are consumed.
Aleurone
Endosperm
-amylase
GA
GA
Water
Scutellum
(cotyledon)
Radicle
Sugar
• Plants produce ethylene in response to
stresses such as drought, flooding,
mechanical pressure, injury, and
infection
• The effects of ethylene include
response to mechanical stress,
senescence, leaf abscission, and fruit
ripening
• Response to gravity is known as
gravitropism
• Roots show positive gravitropism;
shoots show negative gravitropism
• Plants may detect gravity by the settling
of statoliths, specialized plastids
containing dense starch grains
Fig. 39-24
Statoliths
(a) Root gravitropic bending
20 µm
(b) Statoliths settling
• The term thigmomorphogenesis
refers to changes in form that result
from mechanical disturbance
• Rubbing stems of young plants a couple
of times daily results in plants that are
shorter than controls
Fig. 39-26
(a) Unstimulated state
(b) Stimulated state
Side of pulvinus with
flaccid cells
Leaflets
after
stimulation
Pulvinus
(motor
organ)
(c) Cross section of a leaflet pair in the stimulated state (LM)
Side of pulvinus with
turgid cells
Vein