Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 21
Plant Evolution
(Sections 21.5 - 21.8)
Albia Dugger • Miami Dade College
21.5 History of the Vascular Plants
• The oldest fossils of vascular plants are spores that date to
about 450 million years ago (late Ordovician period)
• Early vascular plants stood only a few centimeters high and
had a simple branching pattern, with no leaves or roots
• Fossil Cooksonia
From Tiny Branchers to Coal Forests
• By the early Devonian,
taller species with a
more complex
branching pattern were
common worldwide
From Tiny Branchers to Coal Forests
• Forests of giant seedless vascular plants thrived during the
Carboniferous period – heat and pressure transformed the
remains of these forests to coal
• coal
• Fossil fuel formed over millions of years by compaction
and heating of plant remains
A Carboniferous “Coal Forest”
Rise of the Seed Plants
• Cycads and ginkgos
were among the earliest
gymnosperm lineages
• Early angiosperms such
as magnolias evolved
while dinosaurs walked
on Earth
Reproductive Traits of Seed Plants
• Seed plant sporophytes have pollen sacs, where
microspores form and develop into male gametophytes
(pollen grains)
• Sporophytes also have ovules, where megaspores form and
develop into female gametophytes
Key Terms
• pollen sac
• Of seed plants, reproductive structure in which spermbearing gametophytes (pollen grains) develop
• microspore
• Haploid spore formed in pollen sacs of seed plants;
develops into a sperm-producing gametophyte (a pollen
grain)
Key Terms
• megaspore
• Haploid spore formed in ovule of seed plants
• Develops into an egg-producing gametophyte
• ovule
• Of seed plants, reproductive structure in which eggbearing gametophyte develops
• After fertilization, matures into a seed
How a Seed Forms
How a
Seed
Forms
Microspore in
the pollen sac of
a sporophyte
Megaspore in
the ovule of a
sporophyte
develops into
develops into
Male gametophyte
(pollen grain)
released
Female
gametophyte
in ovule
pollination and fertilization
Seed
(embryo
sporophyte in
mature ovule)
Fig, 21.17, p. 333
Pollination
• A sporophyte releases pollen grains, but holds onto its eggs
• Wind or animals can deliver pollen from one seed plant to the
ovule of another
• pollination
• Delivery of a pollen grain to the egg-bearing part of a seed
plant
Time Line for Plant Evolution
Time Line for Plant Evolution
Bryophyt
es
evolve,
diversify;
seedless
vascular
plants
evolve.
Diversificati
on of
seedless
vascular
plants.
First
treelike
plants
(fern
relatives),
first seed
plants.
Giant
horsetails,
club
mosses
relatives in
swamp
forests.
Conifers
arise late
in period.
Ginkgos,
cycads
evolve. Most
horsetails
and club
mosses die
off by end of
the period.
Adaptive
radiations of
ferns, cycads,
conifers; by
start of
Cretaceous,
conifers the are
dominant trees.
Flowering plants
appear in the early
Cretaceous,
undergo adaptive
radiation, and
become dominant.
Ordovician Silurian Devonian Carboniferous Permian Triassic JurassicCretaceous Tertiary
488
443
416
359
299
251
200
146
66
Millions of years ago (mya)
Fig, 21.13, p. 332
21.6 Gymnosperms—
Plants With Naked Seeds
• Gymnosperms are vascular seed plants that produce seeds
on the surface of ovules
• Seeds are “naked” (not inside a fruit)
• Includes conifers, cycads, ginkgos, and gnetophytes
• gymnosperm
• Seed plant that does not make flowers or fruits
The Conifers
• In conifers, ovules form on the surfaces of woody cones
• Conifers typically have needlelike or scalelike leaves , and
tend to be resistant to drought and cold
• conifer
• Gymnosperm with nonmotile sperm and woody cones
• Examples: pines, redwoods
A Conifer
• Conifers include the
long-lived bristlecone
pines
• One of these trees is
now 4,600 years old
Cycads
• An Australian cycad
with its fleshy seeds
• cycad
• Tropical or subtropical
gymnosperm with
flagellated sperm,
palmlike leaves, and
fleshy seeds
Ginkgo biloba
• Ginkgo’s fleshy seeds
and fan-shaped leaves
• ginkgo
• Deciduous gymnosperm
with flagellated sperm,
fan-shaped leaves, and
fleshy seeds
• One species: Ginkgo
biloba
Gnetophytes
• Ephedra: Yellow
structures on stems are
pollen-bearing cones
• gnetophyte
• Shrubby or vinelike
gymnosperm, with
nonmotile sperm
A Representative Life Cycle:
Ponderosa Pine
• Inside the ovule, a megaspore forms by meiosis and develops
into a female gametophyte
• Male cones hold pollen sacs where microspores develop into
pollen grains
• Pollen grains are released; pollination occurs when one lands
on an ovule, and the pollen grain germinates
• It takes about a year for a pollen tube to grow through ovule
tissue and deliver sperm to the egg
A Representative Life Cycle:
Ponderosa Pine (cont.)
• When fertilization finally occurs, it produces a zygote
• The zygote develops into an embryo sporophyte that, along
with tissues of the ovule, becomes a seed
• The seed is released, germinates, and grows and develops
into a new sporophyte
Life Cycle of a Conifer: Ponderosa Pine
Time
Line
for
Plant
Evolution
1
A seed cone has
many scales, each
with two ovules on its
upper surface
section through one
ovule (the red “cut” in
the diagram to the left)
surface view of
seed cone scale ovule
3 A pollen cone
section
has many scales,
through
each housing a
pollenpollen sac.
producing
sac (red cut)
surface view
of pollen
cone scale
9 Seed is released,
germinates, and the
embryo grows and
develops into a new
sporophyte.
seed coat
embryo
7 One sperm
nucleus fertilizes
the egg, forming
a zygote.
nutritive
tissue
8 Ovule develops
into a mature seed. Fertilization Diploid Stage
Meiosis
Haploid Stage
pollen tube
5 Pollination: 4 Microspores
2 Megaspores
wind
form by meiosis, form by
(view inside ovule)deposits
develop into
meiosis; one
pollen
pollen grains.
sperm-producing
cell
grain
on
6
develops into
eggs
seed cone.
Pollen grain matures into male
the female
female
gametophyte. Two nonflagellated
gametophyte.
sperm nuclei form as pollen tube
gametophyte
grows through ovule tissue.
Fig, 21.19, p. 335
Time Line for Plant Evolution
1 A seed cone has
many scales, each
with two ovules on its
upper surface
section through one
ovule (the red “cut” in
the diagram to the left)
surface view of
seed cone scale ovule
3 A pollen cone
section
has many scales,
through
each housing a
pollenpollen sac.
producing
sac (red cut)
surface view
of pollen
cone scale
9 Seed is released,
germinates, and the
embryo grows and
develops into a new
sporophyte.
seed coat
embryo
7 One sperm
nucleus fertilizes
the egg, forming
a zygote.
nutritive
tissue
8 Ovule develops
Diploid Stage
into a mature seed.
Fertilization
Meiosis
Haploid Stage
pollen tube
5 Pollination: 4 Microspores
2 Megaspores
wind
form by meiosis, form by
(view inside ovule)
deposits
develop into
meiosis; one
pollen
pollen grains.
sperm-producing
cell
grain
on
6
develops into
eggs
seed cone.
Pollen grain matures into male
the female
female
gametophyte. Two nonflagellated
gametophyte.
sperm nuclei form as pollen tube
gametophyte
grows through ovule tissue.
Stepped Art
Fig, 21.19, p. 335
Time Line for Plant Evolution
Fig, 21.19.1, p. 335
Time Line for Plant Evolution
Fig, 21.19.3, p. 335
Time Line for Plant Evolution
Fig, 21.19.9, p. 335
ANIMATION: Pine life cycle
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Key Concepts
• Gymnosperms
• Seed plants make pollen grains that allow fertilization to
occur even in dry times
• They also make eggs in an ovule that develops into a
seed
• Gymnosperms such as pine trees are seed plants with
“naked” seeds – their seeds do not form inside an ovary
21.7 Angiosperms—
The Flowering Plants
• Angiosperms are seed plants that make flowers and fruits
• angiosperms
• Largest seed plant lineage
• Only group that makes flowers and fruits
• flower
• Specialized reproductive shoot of a flowering plant
• fruit
• Mature flowering plant ovary; encloses a seed or seeds
Flowers
• A flower consists of modified leaves arranged in concentric
whorls of sepals and petals
• The stamens of a flower produce pollen.
• Eggs form in the female part of the flower (carpel)
• An ovary at the base of the carpel holds one or more ovules
Key Terms
• stamen
• Male reproductive part of a flower
• carpel
• Female reproductive part of a flower
• ovary
• Of flowering plants, floral chamber that encloses ovule
A Cherry Flower
A Cherry stamen
Flower filament anther
petal (all petals
combined form the
flower’s corolla)
sepal (all sepals
combined form
flower’s calyx)
carpel
stigma
style
ovary
ovule
(forms
within
ovary)
receptacle
Fig, 21.20, p. 336
Pollinators
• Many flowering plants
coevolved with
pollinators
• pollinator
• Animal that moves
pollen, facilitating
pollination
Fruits and Seeds
• After pollination, the flower’s ovary becomes a fruit that
contains one or more seeds
• A flowering plant seed includes an embryo sporophyte and
endosperm, a nutritious tissue
• A variety of dispersal-related traits help disperse seeds to new
habitats where they can thrive
Major Lineages of Flowering Plants
• Two major lineages differ in seed structure and other traits:
• Monocots include orchids, palms, lilies, and grasses
• Eudicots include most herbaceous (nonwoody) plants
such as tomatoes, cabbages, roses, poppies, most
flowering shrubs and trees, and cacti
Key Terms
• monocots
• Lineage of angiosperms with one cotyledon
• Do not produce true wood
• Includes grasses, orchids, and palms
• eudicots
• Lineage of angiosperms with two cotyledons
• Includes herbaceous plants, woody trees, and cacti
Monocot Life Cycle (Lilium)
1. Sporophyte dominates the life cycle
2. Pollen forms inside pollen sacs of stamens
3. Eggs develop in an ovule within an ovary
4. Pollination occurs; a tube grows from the pollen grain into the
ovule, delivering two sperm
5. Double fertilization occurs
6. The resulting seed grows into a sporophyte
Double Fertilization
•
Double fertilization occurs in all flowering plant life cycles
• One sperm fertilizes the haploid egg
• One fertilizes a diploid cell, yielding a triploid cell that
divides to form endosperm, which nourishes the embryo
sporophyte
•
endosperm
• Nutritive triploid tissue in angiosperm seeds
Life Cycle of Lily (Lilium)
Life Cycle of Lily (Lilium)
1 A sporophyte
1
dominates this life
cycle.
2 Pollen forms
6
seedling
pollen sac,
where each
one of many
cells will
give rise to
microspores
seed coat
embryo (2n)
endosperm (3n)
5
seed
Diploid (2n) Phase
Double fertilization Haploid (n) Phase Meiosis
ovules
inside
ovary
cell in ovule
that will give
rise to a
megaspore
Meiosis
2
4
pollen tube
sperm (n)
sperm (n)
pollen tube
delivering
two sperm
to an ovule
ovules inside ovary
pollen grain
(the male
gametophyte)
cell from which
endosperm will
form
3
egg
ovary that
holds many female gametophyte
ovules
inside ovule
inside pollen sacs
of stamens.
3 Eggs develop in an
ovule within an ovary.
4 Pollination
occurs and a tube
grows from the
pollen grain into the
ovule, delivering
two sperm.
5 Double fertilization
occurs in all flowering
plant life cycles. One
sperm fertilizes the
haploid egg. The
other fertilizes a
diploid cell, yielding a
triploid cell that
divides to form
endosperm, a tissue
that nourishes the
embryo sporophyte.
6 The resulting seed
will grow into a new
sporophyte.
Fig, 21.21, p. 337
Life Cycle of Lily (Lilium)
1
6
seedling
seed coat
embryo (2n)
endosperm (3n)
5
seed
Diploid (2n) Phase
Double fertilization
Haploid (n) Phase
pollen sac,
where each
one of many
cells will
give rise to
microspores
ovules
inside
ovary
cell in ovule
that will give
rise to a
megaspore
Meiosis
Meiosis
2
4
pollen tube
sperm (n)
sperm (n)
pollen tube
delivering
two sperm
to an ovule
pollen grain
(the male
gametophyte)
cell from which
endosperm will
form
3
egg
ovary that
holds many female gametophyte
ovules
inside ovule
Stepped Art
Fig, 21.21, p. 337
ANIMATION: Monocot life cycle
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ANIMATION: Flower parts
21.8 Ecological and Economic
Importance of Angiosperms
• Dominant plants in most land habitats, flowering plants are
ecologically important – and essential to human existence
• Angiosperms feed and shelter animals, and they provide us
with food, fabric, oils, medicines, drugs, and more…
Flowering Plants Feed Animals
• Angiosperms provide
food and shelter for a
variety of animals
• This hummingbird is
sipping nectar, which is
mainly sucrose, from a
columbine flower
Angiosperms as Crop Plants
• Nutrient-rich
endosperms of
angiosperm seeds are
staples of human diets
throughout the world
• Mechanized harvesting
of wheat, a monocot
Commercial Products
• Angiosperms supply us
with fiber, wood, and
oils
• Field of cotton, a
eudicot
Medicines and Drugs
• Some flowering plants make secondary metabolites that we
use as medicines or as mood-altering drugs
• secondary metabolite
• Chemical that has no known role in an organism’s normal
metabolism; often deters predation
Secondary Metabolites
• Aspirin, digitalis,
caffeine, nicotine,
pyrethrums, opium
• Marijuana (a eudicot)
growing illegally in
Oregon
Key Concepts
• Angiosperms
• Angiosperms, or flowering plants, are the most recently
evolved seed plants
• They alone make flowers, and their seeds form inside a
floral ovary that develops into a fruit
• Angiosperms are the most widely dispersed and diverse
group of plants
Speaking for the Trees (revisited)
• Every atom of carbon in a tree was taken up from the air in
the form of carbon dioxide
• A tree is about 20 percent carbon by weight, so enormous
amounts of carbon are stored in forests
• Burning forests to make way for agriculture or other uses
adds carbon dioxide to the air, reduces carbon uptake, and
contributes to global warming
Releasing Carbon