Cecie Starr
Christine Evers
Lisa Starr www.cengage.com/biology/starr
(Sections 21.5 - 21.8)
Albia Dugger • Miami Dade College

• 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

• By the early Devonian, taller species with a more complex branching pattern were common worldwide

• 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

• Cycads and ginkgos were among the earliest gymnosperm lineages
• Early angiosperms such as magnolias evolved while dinosaurs walked on Earth

• 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

Microspore in the pollen sac of a sporophyte develops into
Male gametophyte
(pollen grain) released pollination and fertilization
Seed
(embryo sporophyte in mature ovule)
Megaspore in the ovule of a sporophyte develops into
Female gametophyte in ovule
Fig, 21.17, p. 333

• 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

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
488 443 416 359 299 251 200 146 66
Tertiary
Millions of years ago (mya)
Fig, 21.13, p. 332

• 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

• 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

• Conifers include the long-lived bristlecone pines
• One of these trees is now 4,600 years old

• 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

• Ephedra: Yellow structures on stems are pollen-bearing cones
• gnetophyte
• Shrubby or vinelike gymnosperm, with nonmotile sperm

• 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

• 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

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 has many scales, each housing a pollen sac.
section through pollenproducing 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 nutritive tissue
7 One sperm nucleus fertilizes the egg, forming a zygote.
6
8 pollen tube sperm-producing cell
Pollen grain matures into male gametophyte. Two nonflagellated sperm nuclei form as pollen tube grows through ovule tissue.
Ovule develops into a mature seed.
Fertilization
Diploid Stage
Haploid Stage
Meiosis
(view inside ovule) eggs
5 Pollination: wind deposits pollen grain on seed cone.
4 Microspores form by meiosis, develop into pollen grains.
female gametophyte
2 Megaspores form by meiosis; one develops into the female gametophyte.
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
3 A pollen cone has many scales, each housing a pollen sac.
ovule section through pollenproducing 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 nutritive tissue
7 One sperm nucleus fertilizes the egg, forming a zygote.
6
8 pollen tube sperm-producing cell
Pollen grain matures into male gametophyte. Two nonflagellated sperm nuclei form as pollen tube grows through ovule tissue.
Ovule develops into a mature seed.
Fertilization
Diploid Stage
Haploid Stage
Meiosis eggs
5
(view inside ovule)
Pollination: wind deposits pollen grain on seed cone.
4 Microspores form by meiosis, develop into pollen grains.
female gametophyte
2 Megaspores form by meiosis; one develops into the female gametophyte.
Stepped Art
Fig, 21.19, p. 335

Fig, 21.19.1, p. 335

Fig, 21.19.3, p. 335

Fig, 21.19.9, p. 335

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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

• 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

• 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

stamen filament anther stigma carpel style ovary petal (all petals combined form the flower’s corolla) sepal (all sepals combined form flower’s calyx) ovule
(forms within ovary) receptacle
Fig, 21.20, p. 336

• Many flowering plants coevolved with pollinators
• pollinator
• Animal that moves pollen, facilitating pollination

• 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

• 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

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 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

Lilium)

pollen tube delivering two sperm to an ovule
1
6 seedling seed coat embryo (2n) endosperm (3n)
5 seed
Double fertilization
Diploid (2n) Phase
Haploid (n) Phase pollen sac, where each one of many cells will give rise to microspores
Meiosis
2 ovules inside ovary
4 pollen tube sperm (n) sperm (n)
Life Cycle of Lily ( Lilium) cell in ovule that will give rise to a megaspore ovules inside ovary
Meiosis pollen grain
(the male gametophyte) cell from which endosperm will form egg
3 ovary that holds many ovules female gametophyte inside ovule
1
A sporophyte dominates this life cycle.
2 Pollen forms 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

1
Life Cycle of Lily ( Lilium)
6 seedling
Diploid (2n) Phase
Haploid (n) Phase
5 seed coat embryo (2n) endosperm (3n) seed
Double fertilization
4 pollen tube sperm (n) sperm (n) pollen tube delivering two sperm to an ovule pollen sac, where each one of many cells will give rise to microspores
Meiosis
2 cell in ovule that will give rise to a megaspore ovules inside ovary
Meiosis pollen grain
(the male gametophyte) cell from which endosperm will form egg
3 ovary that holds many ovules female gametophyte inside ovule
Stepped Art
Fig, 21.21, p. 337

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• 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…

• Angiosperms provide food and shelter for a variety of animals
• This hummingbird is sipping nectar, which is mainly sucrose, from a columbine flower

• Nutrient-rich endosperms of angiosperm seeds are staples of human diets throughout the world
• Mechanized harvesting of wheat, a monocot

• Angiosperms supply us with fiber, wood, and oils
• Field of cotton, a eudicot

• 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

• 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

• 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