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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 29
Plant Diversity I: How Plants
Colonized Land
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: The Greening of Earth
• For more than the first 3 billion years of Earth’s
history, the terrestrial surface was lifeless
• Cyanobacteria likely existed on land 1.2 billion
years ago
• Around 500 million years ago, small plants,
fungi, and animals emerged on land
• Modern green algae called charophytes are the
closest relatives of land plants they are thought to
share a common ancestor. (1)
© 2011 Pearson Education, Inc.
Evidence that Land Plants Evolved
from Green Algae
• Theyre both multicellular, eukaryotic,
photosynthetic, autotrophs
• Both have cell walls made of cellulose
• Both have chlorophyll a & chlorophyll b
pigments in their chloroplasts
Evidence that Land Plants Evolved
from Charophytes specifically
• Charophytes are the only algae that
share the following characteristics with
plants
– Rings of cellulose-synthesizing proteins
– Peroxisome enzymes
– Structure of flagellated sperm
– Formation of phragmoplast
Figure 29.3 Examples of charophytes, the closest algal relatives
of land plants.
5 mm
Chara species, a pond organism
Coleochaete orbicularis, a
disk-shaped charophyte
that also lives in ponds (LM)
40 m
1 m
Movement onto Land
• Many species of charophytes inhabit
shallow water, so it’s reasonable to
assume that the common ancestor that
diverged into plants & charophyts may
have as well
• Surviving in shallow water requires
organisms to resist occasional drying
• Natural selection would favor individuals
can survive periods of not being
submerged in water
Adaptations Enabling the Move to Land
• In charophytes a layer of a durable polymer called
sporopollenin prevents exposed zygotes from
drying out
• Sporopollenin is also found in plant spore walls
Benefits & Challenges of Moving onto Land
• The movement onto land by charophyte ancestors
provided them unfiltered sun, more plentiful CO2,
nutrient-rich soil, and few herbivores or pathogens
• Land presented challenges: a scarcity of water
and lack of structural support (2)
Derived Traits of Land Plants
(In other words, traits unique to land plants not found in algae)
• Alternation of generations with an
associated trait of multicellular,
dependent embryos
• Walled spores produced in sporangia
• Multicellular gametangia
• Apical meristems
Alternation of Generations and Multicellular,
Dependent Embryos
• Plants alternate between two multicellular stages,
a reproductive cycle called alternation of
generations
• The gametophyte is haploid and produces
haploid gametes by mitosis
• Fusion of the gametes gives rise to the diploid
sporophyte, which produces haploid spores by
meiosis (Start of 3 continues for several slides)
• The diploid zygote develops into a multicellular
embryo within the tissue of the female
gametophyte
• This provides the developing embryo with
nutrients
– Nutrients are transferred from parent to embryo through
placental transfer cells
– Placental transfer cells are similar in function to the
mammalian placenta
• Land plants are called embryophytes because of
the dependency of the embryo on the parent
© 2011 Pearson Education, Inc.
Figure 29.5a
Gametophyte
(n)
Mitosis
n
Gamete from
another plant
Mitosis
n
FERTILIZATION
2n
Sporophyte
(2n)
Haploid (n)
Diploid (2n)
n Spore Gamete n
MEIOSIS
Key
Zygote
Mitosis
Alternation of generations
1 m
Walled Spores Produced in Sporangia
• The multicellulr diploid sporophyte produces
haploid spores in organs called sporangia
• Diploid cells called sporocytes undergo meiosis
to generate haploid spores
– Sporocytes are equivalent to the human germ cells in
that they are diploid cells that give rise to a haploid cell
• Spore walls contain sporopollenin, which makes
them resistant to harsh environments and allows
them to be dispersed in the air
© 2011 Pearson Education, Inc.
Figure 29.5c
Spores
Sporangium
Longitudinal section of
Sphagnum sporangium (LM)
Sporophyte
Gametophyte
1 m
Sporophytes and sporangia of Sphagnum (a moss)
Multicellular Gametangia
• Gametes are produced within multicellular hapliod
organs called gametangia
• Female gametangia, called archegonia
– produce eggs
– are the site of fertilization
– Location where zygote develops into embryo
• Male gametangia, called antheridia
– produce and release sperm
– Many sperm have flagella to allow them to swim to an
egg
© 2011 Pearson Education, Inc.
Figure 29.5d
Female
gametophyte
Archegonia,
each with an
egg (yellow)
Antheridia
(brown),
containing
sperm
Male
gametophyte
Archegonia and antheridia of Marchantia (a liverwort)
1 m
Apical Meristems
• Localized regions of cell division at the tips of
roots and shoots where plants sustain continual
growth
• Cells from the apical meristems differentiate into
various tissues (End 3)
© 2011 Pearson Education, Inc.
Figure 29.5e
Apical meristem
of shoot
Developing
leaves
Apical meristems of plant
roots and shoots
Apical
meristem
of root
Root
100 m
Shoot
1 m
100 m
• Additional derived traits include
 Cuticle, a waxy covering of the epidermis
 Mycorrhizae,
 Early land plants lacked roots and leaves. Without roots
they relied on symbiotic associations between fungi and
land plants that may have helped to obtain nutrients
 Mycorrhizal fungi form extensive networks of filaments
throughout the soil allowing them to efficiently uptake
nutrients
 The fungi then transfer the nutrients to their symbiotic
partner
© 2011 Pearson Education, Inc.
Table 29. 1
Vascular tissue refers to the cells joined to form tubes for
transporting nutrients & water
Seed: and embryo packaged with a supply of nutrients inside a protective coat
Gymnosperms: termed naked
seed plants because their
seeds are NOT enclosed in
1chambers
m
Angiosperms: flowering plants
Nonvascular plants have life cycles
dominated by gametophytes
• The gametophyte is usually larger and
longer living than the sporophyte in
nonvascular plants
• Bryophyte sperm are flagellated and
require water to migrate to an egg
• Bryophyte gameotphytes typically
produce ground covering mosses
– Their bodies are too thin to support a tall plant
– Lack vascular tissue for nutrient transport over
long distances
Bryophyte Sporophytes
• Can’t live independently of the gametophyte
which supplies them with nutrients
• Has 3 main structures
– Foot: absorbs nutrients from gametophyte
– Seta: conducts minerals to sporangium
– Sporangium:produces up to 50 million spores by
meiosis
– Stomata: specialized pores that open and close
to support photosynthesis by allowing exchange
of CO2 & O2
Figure 29.13-3
(24-25)
Key
Haploid (n)
Diploid (2n)
MEIOSIS
Spore
dispersal
Spore
(n)
Rhizoid
Underside
of mature
gametophyte
(n)
Sporangium
Sporangium
Antheridium
Young
gametophyte
Mature
sporophyte
(2n)
Sorus
New
sporophyte
Sperm
Archegonium
Egg
Zygote
(2n)
Gametophyte
Fiddlehead (young leaf)
1 m
FERTILIZATION
Derived Traits of Seedless Vascular Plants
• True roots
• The ability to grow taller shoots
• Vascular tissue
– Xylem
– Phloem
• Leaves
• A dominant sporophyte (diploid)
generation
• Lignified tissue
Seedless Vascular Plants
• The sperm of ferns and all other
seedless vascular plants are flagellated
and so these plants typically grow in
moist environments
• Unlike nonvascular plants, these have
sporophytes that weren’t dependent on
the gametophyte
– Branching sporophytes with multiple complex
sporangia would compete for space and light
– Natural selection would favor individuals capable
of growing taller
Life Cycle with Dominant Sporophytes
• Fossils suggest that ancestors of
vascular plants had gametophytes and
sporophytes that were equal in size
• Today, all extant species of vascular
plants have a dominant sporophyte
generation that is larger and more
complex than the gametophyte
2 Types of Vascular Tissue
• Phloem
– Cells arranged in tubes to distribute sugars, amino
acids, and other organic products
• Xylem
– Conducts most water and minerals
– Includes tracheids: tube shaped cells that
carry water & minerals up from the roots
– Water conducting cells have their cell walls
strengthened by a polymer called lignin
Evolution of Roots
• Lignified tissue allowed plants to grow
taller by providing more support, and
also allowed for the evolution of roots
– Roots are organs that absorb water and
nutrients from the soil
– Roots also anchor vascular plants allowing
shoots to grow taller
Evolution of Leaves
• Leaves increase surface area of the
plant body and are the primary sites of
photosynthesis
• Can be classified as microphylls or
megaphylls depending on size &
complexity
– Microphylls: usually small and spine
shaped supported by a single strand of
vascular tissue
– Megaphylls: leaves with highly branched
vascular system
Sporophylls & Spore Variations
Sporophylls: modified leaves that bear sporangia
Homosporous
Heterosporous
• Most seedless vascular
plants are homosporous
• All seed plants
• Have 2 types of sporangium
that produces 2 types of
spores
– Ferns
• Homosporous plants
have 1 type of
sporangium that
produces 1 type of spore
that typically develops
into a bisexual
gametophyte
– Megasporophylls produce
Megaspores which develop
into female gametophytes
which make eggs
– Microsporangia produce
microspores which develop
into male gametophytes which
produce sperm
LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 30
Plant Diversity II: The Evolution
of Seed Plants
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Gymnosperms & Angiosperms
• There are 2 groups of seed plants that
are classified based on if their seeds
are enclosed in ovaries as in
angiosperms, or “naked” as in
gymnosperms
Seeds & Pollen Grains are Key
Adaptations for Life on Land
• Seeds consist of an embryo and its food
supply surrounded by a protective coat
• Because it nourishes and protects the
embryo but can move away from the
parent plant its analogous to a
detachable uterus
Traits Common to All Seed Plants
• Reduced gametophytes
– Smaller gametophytes develop from spores
retained within the protective sporangium of the
sporophyte nourishing and protecting them from
harsh environmental conditions
• Heterospory
• Ovules & Pollen
Ovules & Pollen
Ovules
• Seed plants retain the
megasporangium within
the sporophyte (unlike
seedless plants which
release them)
• Ovules consist of the
entire structure containing
the megasporangium,
megaspore, and
intugement
• Each produces 1 or more
eggs
Pollen
• Microspores develop into a
pollen grain that contains the
gametophyte enclosed within
the pollen wall (containing
sporopollenin)
• This allows the male
gametophyte to move via
wind or animal to an egg,
where it will produce sperm
• Pollen is NOT dependent on
water for spreading to eggs
Reproductive Adaptations of
Angiosperms Include Flowers & Fruit
• Angiosperms are seed plants that
produce reproductive structures such as
flowers & fruit
• Angiosperms may be wind pollinated
(grasses), or pollinated with insect/
animal helpers who carry pollen from 1
plant to another (bees and lilac)
Characteristics of Angiosperms:
Flowers
• The flower is an angiosperm shoot
specialized for sexual reproduction
• Flowers can have up to 4 rings of
modified leaves (sporophylls) called
floral organs
– Sepals
– Petals
– Carpels
– Stamen
Sterile Floral Organs
sepals
• Usually green and
enclose the flower before
it blooms
• Think rosebud
petals
• Brightly colored leaves
that aid in attracting
pollinators
Fertile Floral Organs: Stamen
• Produce microspores that develop into pollen grains
containing gametophytes
• Consists of a stalk called a filament and a terminal
anther where pollen is produced
• Each pollen grain contains a male gametophyte
consisting of 2 haploid cells one divides to form 2 sperm,
the other, a tube cell produces the pollen tube
• These are male organs think staMEN & MANther
Fertile Floral Organs: Carpel
• Make megaspores & their products, female
gametophytes
– Flowers may have a single carpel or multiple
carpels, which can be separate or fused
– A single carpel or group of fused carpels is called
a pistil
• Stigma: the sticky tip of the carpel that recieves
pollen
• Style: leads the stigma to the ovary
• Ovary: contains 1 or more ovules which when
fertilized will develop into a seed
Figure 38.2a
(1)
Stamen
Anther
Filament
Petal
Stigma Carpel
Style
Ovary
Sepal
Receptacle
(a) Structure of an idealized flower
Fruits: Mature Ovaries
• As seeds develop from fertilized ovules,
the ovary wall thickens
• Fruits protect dormant seeds & aid in
their dispersal
– twirly-birds and dandelions help seeds float
– Burrs stick to animal fur
– Apples are tasty so that animals eat and
then deposit seeds along with “natural
fertilizer” far away from parent plant
• Fruit can be fleshy (apple) or dry
(milkweed pod)
Pollintation
• After its release from the anther, pollen
is carried to the sticky stigma at the top
of the carpel
• The pollen grain then absorbs water
and germinates after adherence
allowing the tube cell to produce a
pollen tube that grows down to the style
of the carpel where the pollen tube will
penetrate to the ovule and discharge 2
sperm
Double Fertilization
• One sperm fertilizes the egg forming a
diploid zygote
• Zygote develops into sporophyte embryo with a
rudimentary root and 1 or 2 leaves called
cotyledons
• The other sperm fuses with 2 nuclei at
the center of the female gametophyte
producing a triploid cell
– develops into endosperm, tissue rich in
starch and other foods to nourish the
embryo
Function of Double Fertilization
• May synchronize the development of
food storage in the seed with the
development of the embryo
– There’s no endospore without fertilization
– This prevents plants from wasting energy
and nutrients on infertile ovules
Self-Pollination vs Cross-Pollination
• Crosspollination increases genetic
variation
• Some plants have mechanisms to help
ensure cross pollination instead of self
pollination
– In some species, stamens and carpels of a
single flower mature at different times
– In other species, stamen and carpels are
arranged to discourage self-pollination
Monocots vs Dicots
• Monocots have 1 seed leaf
• When they mature they usually have leaves with
parallel veins
– Blade of grass
• Dicots have 2 seed leaves
– Usually have adult leaves with branching
leaf veins
– Oak leaf
Evolutionary Links Between
Angiosperms & Animals
• Animals and plants have influenced
each others evolution since they moved
onto land
• For example, herbivores can reduce a
plants reproductive success by eating
its roots, leaves, or seeds
• Some plants evolve defenses against
herbivores, or adaptations to attract
pollinators
Evolutionary Links Between
Angiosperms & Animals
• Coevolution: the process of reciprocal
evolutionary change that occurs
between pairs of species or among
groups of species as they interact with
one another.
• The activity of each species that
participates in the interaction applies
selection pressure to the others
Evolutionary Links Between
Angiosperms & Animals
• Coevolution can even affect the rate of
speciation
• Example: Flower petal arrangement
– Flower petals can be arranged with
bilateral symmetry or radial symmetry
On a flower with
bilateral symmetry,
an insect pollinator
may only be able to
obtain nectar by
approaching the
plant from a certain
direction that
increases likelihood
pollen will be picked
up by the parts of
the insect body that
will come into
contact with the
stigma of a flower
On average, a clade with
bilaterally symmetrical
flowers has nearly 2,400
more species than a
similar clade with radially
symmetrical flowers
LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 38
Angiosperm Reproduction
and Biotechnology
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Concept 38.1: Flowers, double fertilization,
and fruits are unique features of the
angiosperm life cycle
• Plant lifecycles are characterized by the alternation
between a multicellular haploid (n) generation and
a multicellular diploid (2n) generation
• Diploid sporophytes (2n) produce spores (n) by
meiosis; these grow into haploid gametophytes (n)
• Gametophytes produce haploid gametes (n) by
mitosis; fertilization of gametes produces a
sporophyte
Video: Flower Blooming (time lapse)
© 2011 Pearson Education, Inc.
• In angiosperms, the sporophyte is the dominant
generation, the large plant that we see
• The gametophytes are reduced in size and
depend on the sporophyte for nutrients
• The angiosperm life cycle is characterized by
“three Fs”: flowers, double fertilization, and fruits
Video: Flower Plant Life Cycle (time lapse)
© 2011 Pearson Education, Inc.
Figure 38.2a
(1)
Stamen
Anther
Filament
Petal
Stigma Carpel
Style
Ovary
Sepal
Receptacle
(a) Structure of an idealized flower
Flower Structure and Function
• Flowers are the reproductive shoots of the
angiosperm sporophyte; they attach to a part of
the stem called the receptacle
• Flowers consist of four floral organs: sepals,
petals, stamens, and carpels
• Stamens and carpels are reproductive organs;
sepals and petals are sterile
© 2011 Pearson Education, Inc.
• A stamen consists of a filament topped by an
anther with pollen sacs that produce pollen
• A carpel has a long style with a stigma on which
pollen may land
• At the base of the style is an ovary containing one
or more ovules
• A single carpel or group of fused carpels is called
a pistil
© 2011 Pearson Education, Inc.
Development of Male Gametophytes in
Pollen Grains
• Pollen develops from microspores within
the microsporangia, or pollen sacs, of anthers
• Each microspore undergoes mitosis to produce
the male gametophyte, which has two cells: the
generative cell and the tube cell
• Generative cell eventually gives rise to two sperm
cells, and the tube cell gives rise to the pollen
tube.
• A complete pollen grain consists of the two-celled
male gametophyte and the spore wall (2-6)
© 2011 Pearson Education, Inc.
• If pollination succeeds, a pollen grain produces a
pollen tube that grows down into the ovary and
discharges two sperm cells near the embryo sac
Video: Bee Pollinating
Video: Bat Pollinating Agave Plant
© 2011 Pearson Education, Inc.
Figure 38.3
(a) Development of a male
gametophyte
(in pollen grain)
(b) Development of a female
gametophyte (embryo sac)
Microsporangium
(pollen sac)
(7)
Megasporangium
Microsporocyte
Ovule
MEIOSIS
Megasporocyte
Integuments
Microspores (4)
Micropyle
Surviving
megaspore
Each of 4
microspores
Ovule
Male
gametophyte
(in pollen grain)
Generative cell
(will form 2
sperm)
Antipodal cells (3)
Polar nuclei (2)
Egg (1)
Nucleus of tube cell
Integuments
20 m
(LM)
Key to labels
Haploid (n)
Diploid (2n)
100 m
75 m
Ragweed
pollen
grain
(colorized
SEM)
Synergids (2)
Embryo sac
(LM)
Female gametophyte
(embryo sac)
MITOSIS
Development of Female Gametophytes
(Embryo Sacs)
• The embryo sac, or female gametophyte,
develops within the ovule
• Within an ovule, two integuments surround a
megasporangium
• One cell in the megasporangium undergoes
meiosis, producing four megaspores, only one of
which survives
• The megaspore divides, producing a large cell
with eight nuclei (8)
© 2011 Pearson Education, Inc.
Figure 38.3b
(b) Development of a female gametophyte
(embryo sac)
Megasporangium
Ovule
MEIOSIS
Megasporocyte
Integuments
Micropyle
Surviving
megaspore
Ovule
Antipodal cells (3)
Polar nuclei (2)
Egg (1)
Integuments
Synergids (2)
Haploid (n)
Diploid (2n)
100 m
Key to labels
Embryo sac
(LM)
Female gametophyte
(embryo sac)
MITOSIS
Pollination
• In angiosperms, pollination is the transfer of
pollen from an anther to a stigma
• Pollination can be by wind, water, or animals
• Wind-pollinated species (e.g., grasses and many
trees) release large amounts of pollen
• (9) Video Animation
© 2011 Pearson Education, Inc.
Figure 38.4a
Abiotic Pollination by Wind
Pollination by Bees
Common dandelion
under normal light
Hazel staminate flowers
(stamens only)
Hazel carpellate
flower (carpels only)
(10 Here and
on next slide)
Common dandelion
under ultraviolet light
Figure 38.4b
Pollination by Moths
and Butterflies
Pollination by Flies
Pollination by Bats
Anther
Moth
Fly egg
Stigma
Moth on yucca flower
Blowfly on carrion
flower
Pollination by Birds
Hummingbird
drinking nectar of
columbine flower
Long-nosed bat feeding
on cactus flower at night
Coevolution of Flower and Pollinator
• Coevolution is the evolution of interacting species
in response to changes in each other
• Many flowering plants have coevolved with
specific pollinators
• The shapes and sizes of flowers often correspond
to the pollen transporting parts of their animal
pollinators
– For example, Darwin correctly predicted a moth
with a 28 cm long tongue based on the
morphology of a particular flower (11)
© 2011 Pearson Education, Inc.
Figure 38.5
Double Fertilization
• After landing on a receptive stigma, a pollen grain
produces a pollen tube that extends between the
cells of the style toward the ovary
• Double fertilization results from the discharge of
two sperm from the pollen tube into the embryo
sac
• One sperm fertilizes the egg, and the other
combines with the polar nuclei, giving rise to the
triploid food-storing endosperm (3n)
Animation: Plant Fertilization
© 2011 Pearson Education, Inc.
Figure 38.6-3
2
1
Stigma
Pollen
grain
Pollen
tube
Ovule
2 sperm
Polar
nuclei
Style
Ovary
3
Endosperm
nucleus (3n)
(2 polar nuclei
plus sperm)
Egg
Ovule
Synergid
Polar
nuclei
Zygote
(2n)
2 sperm
Egg
Micropyle
(12-16)
Endosperm Development
• Endosperm development usually precedes
embryo development
• In most monocots and some eudicots, endosperm
stores nutrients that can be used by the seedling
• In other eudicots, the food reserves of the
endosperm are exported to the cotyledons
• After double fertilization, each ovule develops into
a seed
• The ovary develops into a fruit enclosing the
seed(s) (17-20)
© 2011 Pearson Education, Inc.
Embryo Development
• The first mitotic division of the zygote splits the
fertilized egg into a basal cell and a terminal cell
• The basal cell produces a multicellular suspensor,
which anchors the embryo to the parent plant
• The terminal cell gives rise to most of the embryo
• The cotyledons form and the embryo elongates
Animation: Seed Development
© 2011 Pearson Education, Inc.
Figure 38.7
Ovule
Proembryo
Endosperm
nucleus
Integuments
Zygote
Suspensor
Cotyledons
Basal
cell
Shoot
apex
Root
apex
Terminal cell
Basal cell
Zygote
Suspensor
Seed
coat
Endosperm
Figure 38.7a
Ovule
Endosperm
nucleus
Integuments
Zygote
Terminal cell
Basal cell
Zygote
Figure 38.7b
Proembryo
Suspensor
Cotyledons
Basal
cell
Shoot
apex
Root
apex
Suspensor
Seed
coat
Endosperm
Structure of the Mature Seed
• The embryo and its food supply are enclosed by a
hard, protective seed coat
• The seed enters a state of dormancy
• A mature seed is only about 5–15% water main
mechanism for maintaining dormancy along with
rigid seed coat.
• Once dormancy is broken the first organ to
emerge is the radicle, or embryonic root. (21-23)
© 2011 Pearson Education, Inc.
• In some eudicots, such as the common garden
bean, the embryo consists of the embryonic axis
attached to two thick cotyledons (seed leaves)
• Below the cotyledons the embryonic axis is called
the hypocotyl and terminates in the radicle
(embryonic root); above the cotyledons it is called
the epicotyl
• The plumule comprises the epicotyl, young leaves,
and shoot apical meristem
© 2011 Pearson Education, Inc.
Figure 38.8
Seed coat
Epicotyl
Hypocotyl
Radicle
Cotyledons
(a) Common garden bean, a eudicot with thick cotyledons
Seed coat
(24 Here
and on
next slide)
Endosperm
Cotyledons
Epicotyl
Hypocotyl
Radicle
(b) Castor bean, a eudicot with thin cotyledons
Scutellum
(cotyledon)
Coleoptile
Coleorhiza
Pericarp fused
with seed coat
Endosperm
Epicotyl
Hypocotyl
Radicle
(c) Maize, a monocot
Figure 38.9a
Foliage leaves
Cotyledon
Hypocotyl
Cotyledon
Epicotyl
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
(a) Common garden bean
Seed Dormancy: An Adaptation for Tough
Times
• Seed dormancy increases the chances that
germination will occur at a time and place most
advantageous to the seedling
• The breaking of seed dormancy often requires
environmental cues, such as temperature or
lighting changes
• Germination depends on imbibition, the uptake of
water due to low water potential of the dry seed
• The radicle (embryonic root) emerges first
• Next, the shoot tip breaks through the soil surface
(25)
© 2011 Pearson Education, Inc.
Fruit Form and Function
• A fruit develops from the ovary
• It protects the enclosed seeds and aids in seed
dispersal by wind or animals
• A fruit may be classified as dry, if the ovary dries
out at maturity, or fleshy, if the ovary becomes
thick, soft, and sweet at maturity (26)
Animation: Fruit Development
© 2011 Pearson Education, Inc.
• Fruit dispersal mechanisms include
– Water
– Wind
– Animals (27 Examples on following slides)
© 2011 Pearson Education, Inc.
Figure 38.11a
Dispersal by Wind
Dandelion fruit
Dandelion “seeds” (actually one-seeded fruits)
Tumbleweed
Winged seed of
the tropical Asian
climbing gourd
Alsomitra macrocarpa
Winged fruit of a maple
Dispersal by Water
Coconut seed embryo,
endosperm, and endocarp
inside buoyant husk
Figure 38.11b
Dispersal by Animals
Fruit of puncture vine
(Tribulus terrestris)
Squirrel hoarding
seeds or fruits
underground
Ant carrying
seed with nutritious
“food body” to its
nest
Seeds dispersed in black bear feces
Asexual Reproduction
• Fragmentation: when detached
vegetative fragments develop into new
offspring
• Apomixis: asexual production of seeds
without pollination or fertilization
Advantages
Asexual Reproduction
Sexual Reproduction
• Generates variation in
• No need for pollinator
offspring and populations that
• Allows plants to pass on all
is advantageous in unstable
genes intact to progeny, so
or changing environments
if a plant is already well
adapted to the environment • Seeds which are more
common with this type of
and the environment isn’t
re[production facilitate
changing, that’s a benefit
dispersal to more distant
• Produces stronger
locations
seedlings
• Seed dormancy allows
growth to be suspended until
conditions are favorable
Disadvantages
Asexual Reproduction
Sexual Reproduction
• Genotypic uniformity puts • There is great amount of
energy expenditure in sexual
populations at greater risk
reproduction
of local extinction if there is
catastrophic environmental
change or disease
• Often requires interactions
with pollinators
• Without seeds, plants can’t
disperse as well
• New combinations of genes
may not be as fit as parental
combinations
Mechanisms to Prevent Self Fertilization
Dioecious
Self-Incompatibility
• Individuals either produce
flowers with stamen, or
flowers with carpels but
not both
• The ability of a plant to
reject its own pollen
• Sometimes individuals
produce both stamen and
carpels, but they mature
ate different times
• Recognition of self pollen
is based on genes for
self-incompatibility called
s-genes
Vegetative Propagation & Agriculture
• Clones from cuttings
• Grafting
• Test-tube cloning
– GMs
– Transgenic plants
Plant Biotechnology & Genetic
Engineering
• Transgenic: genetically modified
organisms that have been engineered
to express a gene from another species
– Reducing world hunger
– Reducing fossil fuel dependancy
Debate Over Plant Biotechnology
• Issues of Human Health
• Possible Effects on Non-target Organisms
– Pollen from transgenic corn gets on milkweed
plants and kills the Monarch butterflies that feed
off of them
• Transgene Escape
– Transgenes may escape the intended crop and
get into weeds or other plants through horizontal
gene transfer or spontaneous hybridization