Chapter 21 Plant Evolution (Sections 21.5 - 21.8)
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Transcript of Chapter 21 Plant Evolution (Sections 21.5 - 21.8)
Albia Dugger • Miami Dade College
Cecie StarrChristine EversLisa Starr
www.cengage.com/biology/starr
Chapter 21Plant Evolution
(Sections 21.5 - 21.8)
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 sperm-
bearing 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 egg-
bearing gametophyte develops• After fertilization, matures into a seed
How a Seed Forms
Fig, 21.17, p. 333
Seed (embryo
sporophyte in mature ovule)
pollination and fertilization
Male gametophyte (pollen grain)
released
develops into
Microspore in the pollen sac of
a sporophyte
develops into
Female gametophyte
in ovule
Megaspore in the ovule of a sporophyte
How a Seed Forms
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
Fig, 21.13, p. 332
Millions of years ago (mya)
Tertiary416
Ordovician Silurian Devonian Carboniferous Permian Triassic JurassicCretaceous66146200251299359443488
Bryophytes evolve, diversify;seedless vascular plants evolve.
Diversification of seedless vascular 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 offerns, cycads, conifers; by start of Cretaceous, conifers the are dominant trees.
Flowering plants appear in the early Cretaceous, undergo adaptive radiation, and become dominant.
First treelike plants (fern relatives), first seed plants.
Time Line for Plant Evolution
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
Fig, 21.19, p. 335
Pollen grain matures into male gametophyte. Two nonflagellated sperm nuclei form as pollen tube grows through ovule tissue.
sperm-producing cell
Megaspores form by meiosis; one develops into the female gametophyte.
Pollination: wind deposits pollen grain on seed cone.
(view inside ovule)
pollen tube
One sperm nucleus fertilizes the egg, forming a zygote.
Ovule develops into a mature seed.
Seed is released, germinates, and the embryo grows and develops into a new sporophyte. nutritive
tissue
surface view of pollen cone scale
section through pollen-producing sac (red cut)
A pollen cone has many scales, each housing a pollen sac.
surface view of seed cone scale ovule
section through one ovule (the red “cut” in the diagram to the left)
A seed cone has many scales, each with two ovules on its upper surface
Microspores form by meiosis, develop into pollen grains.
seed coat
embryo
female gametophyte
eggs
MeiosisFertilization Haploid StageDiploid Stage
1
2
3
45
6
7
8
9
Time Line for Plant Evolution
One sperm nucleus fertilizes the egg, forming a zygote.
Seed is released, germinates, and the embryo grows and develops into a new sporophyte. nutritive
tissue
seed coat
embryo7
9
Ovule develops into a mature seed. Fertilization
8
Megaspores form by meiosis; one develops into the female gametophyte.
section through pollen-producing sac (red cut)
ovule
section through one ovule (the red “cut” in the diagram to the left)
Microspores form by meiosis, develop into pollen grains.
MeiosisHaploid StageDiploid Stage
24
Pollen grain matures into male gametophyte. Two nonflagellated sperm nuclei form as pollen tube grows through ovule tissue.
sperm-producing cell
(view inside ovule)
pollen tube
female gametophyte
eggs
5
6
Pollination: wind deposits pollen grain on seed cone.
surface view of pollen cone scale
A pollen cone has many scales, each housing a pollen sac.
A seed cone has many scales, each with two ovules on its upper surface
1
3
surface view of seed cone scale
Fig, 21.19, p. 335
Stepped Art
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
Time Line for Plant Evolution
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
Fig, 21.20, p. 336
sepal (all sepals combined form flower’s calyx)
petal (all petals combined form the flower’s corolla)
receptacle
ovule(forms within ovary)
style
stamen carpel
filament anther stigma ovary
A Cherry Flower
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)
Fig, 21.21, p. 337
female gametophyte inside ovule
ovary that holds many ovules
pollen tube delivering two sperm to an ovule
egg
cell from which endosperm will form
pollen grain (the male gametophyte)
sperm (n)
MeiosisHaploid (n) PhaseDouble fertilization
cell in ovule that will give rise to a megaspore
ovules inside ovary
pollen sac, where each one of many cells will give rise to microspores
seed
embryo (2n)
seedling
pollen tubesperm (n)
Diploid (2n) Phase Meiosis
seed coat
endosperm (3n)
ovules inside ovary
The resulting seed will grow into a new sporophyte.
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.
Pollination occurs and a tube grows from the pollen grain into the ovule, delivering two sperm.
Eggs develop in an ovule within an ovary.
Pollen forms inside pollen sacs of stamens.
A sporophyte dominates this life cycle.
1
2
3
4
5
1
2
3
4
5
6
6
Life Cycle of Lily (Lilium)
female gametophyte inside ovule
egg
cell from which endosperm will form
pollen grain (the male gametophyte)
MeiosisHaploid (n) Phase
Meiosis
2
3
cell in ovule that will give rise to a megaspore
ovules inside ovary
pollen sac, where each one of many cells will give rise to microspores
Diploid (2n) Phase
1
pollen tube delivering two sperm to an ovule
sperm (n)
Double fertilization
pollen tubesperm (n)
4
ovary that holds many ovules
seed
embryo (2n)
seedling
seed coat
endosperm (3n)5
6
Fig, 21.21, p. 337
Stepped Art
Life Cycle of Lily (Lilium)
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