biology in focus - chapter 26
TRANSCRIPT
CAMPBELL BIOLOGY IN FOCUS
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Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge
26The Colonization of Land by Plants and Fungi
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Overview: The Greening of Earth
For more than the first 2 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
The first forests formed about 385 million years ago
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Figure 26.1
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Although not closely related, plants and fungi colonized the land as partners before animals arrived
Plants supply oxygen and are the ultimate source of most food eaten by land animals
Fungi break down organic material and recycle nutrients
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Figure 26.2
Charophytealgae
Fungi
Animals
Plants
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Concept 26.1: Fossils show that plants colonized land more than 470 million years ago
Green algae called charophytes are the closest relatives of land plants
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Evidence of Algal Ancestry
Many characteristics of land plants also appear in some algae
However, land plants share certain distinctive traits with only charophytes, including Rings of cellulose-synthesizing complexes Structure of flagellated sperm
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Figure 26.3
30 nm
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Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants
Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes
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Figure 26.4
40 m
Coleochaete orbicularis, adisk-shaped charophyte thatalso lives in ponds (LM)
Chara vulgaris, a pond organism
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Figure 26.4a
Chara vulgaris, a pond organism
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Figure 26.4b
40 mColeochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM)
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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 The movement onto land by charophyte ancestors
provided unfiltered sunlight, more plentiful CO2, and nutrient-rich soil
Land presented challenges: a scarcity of water and lack of structural support
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The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants
Systematists are currently debating the boundaries of the plant kingdom
Until this debate is resolved, we define plants as embryophytes, plants with embryos
Animation: Moss Life Cycle
Animation: Fern Life Cycle
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Figure 26.5
ANCESTRALALGA
Red algae
Chlorophytes
Plantae
Charophytes
Embryophytes
ViridiplantaeStreptophyta
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Derived Traits of Plants
Key traits that appear in nearly all land plants but are absent in the charophytes include Alternation of generations Multicellular, dependent embryos Walled spores produced in sporangia Apical meristems
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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
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Figure 26.6
FERTILIZATIONMEIOSIS
Key
Alternation of generations
Mitosis
Gametophyte(n)
Gamete fromanother plant
Wall ingrowths
Mitosis
Spore Gamete
Zygote
MitosisSporophyte(2n)
Placental transfercell (blue outline)
Multicellular, dependent embryos
EmbryoMaternal tissue
Haploid (n)Diploid (2n)
10 m2 m
2n
n
n
n
n
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Figure 26.6a
FERTILIZATIONMEIOSIS
Key
Alternation of generations
Mitosis
Gametophyte(n)
Gamete fromanother plant
Mitosis
Spore Gamete
Zygote
MitosisSporophyte(2n)
Haploid (n)Diploid (2n)
2n
n
n
n
n
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Figure 26.6b
Wall ingrowthsPlacental transfercell (blue outline)
Multicellular, dependent embryos
EmbryoMaternal tissue
10 m2 m
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Figure 26.6ba
EmbryoMaternaltissue
10 m
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Figure 26.6bb
Wall ingrowthsPlacental transfercell (blue outline)
2 m
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Multicellular, dependent embryos The multicellular, diploid embryo is retained within the
tissue of the female gametophyte Nutrients are transferred from parent to embryo
through placental transfer cells Land plants are called embryophytes because of the
dependency of the embryo on the parent
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Walled spores produced in sporangia Sporangia are multicellular organs that produce
spores Spore walls contain sporopollenin, which makes them
resistant to harsh environments
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Figure 26.7
Gametophyte
Sporophyte
SporangiumSpores
Longitudinal section ofSphagnum sporangium(LM)
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Figure 26.7a
Gametophyte
Sporophyte
Sporangium
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Figure 26.7b
SporangiumSpores
Longitudinal section ofSphagnum sporangium(LM)
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Apical meristems Localized regions of cell division at the tips of roots
and shoots are called apical meristems Apical meristem cells can divide throughout the
plant’s life
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Additional derived traits include Cuticle, a waxy covering of the epidermis that
functions in preventing water loss and microbial attack
Stomata, specialized pores that allow the exchange of CO2 and O2 between the outside air and the plant
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Early Land Plants
Fossil evidence indicates that plants were on land at least 470 million years ago
Fossilized spores and tissues have been extracted from 450-million-year-old rocks
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Figure 26.8
(a) Fossilizedspores
(b) Fossilizedsporophytetissue
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Figure 26.8a
(a) Fossilizedspores
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Figure 26.8b
(b) Fossilizedsporophytetissue
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Large plant structures, such as the sporangium of Cooksonia, appeared in the fossil record 425 million years ago
By 400 million years ago, a diverse assemblage of plants lived on land
Unique traits in these early plants included specialized tissues for water transport, stomata, and branched sporophytes
Animation: Fungal Reproduction Nutrition
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Figure 26.UN01
Cooksonia sporangium fossil (425 millionyears old)
0.3 mm
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Figure 26.9
Sporangia
Rhizoids
25 m
2 cm
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Figure 26.9a
25 m
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Concept 26.2: Fungi played an essential role in the colonization of land
Fungi may have colonized land before plants Mycorrhizae are symbiotic associations between
fungi and land plants that may have helped plants without roots to obtain nutrients
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Fungal Nutrition
Fungi are heterotrophs and absorb nutrients from outside of their body
Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds
Fungi can digest compounds from a wide range of sources, living or dead
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Adaptations for Feeding by Absorption
Fungal cell walls contain chitin, a strong but flexible nitrogen-containing polysaccharide
The most common body structures are multicellular filaments and single cells (yeasts)
Some species grow as either filaments or yeasts; others grow as both
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The morphology of multicellular fungi enhances their ability to absorb nutrients
Fungi consist of mycelia, networks of branched hyphae, filiments adapted for absorption
A mycelium’s structure maximizes its surface-area-to-volume ratio
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Figure 26.10
Hyphae
Mycelium
60 m
Reproductivestructure
Spore-producingstructures
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Figure 26.10a
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Figure 26.10b
Mycelium
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Figure 26.10c
60 m
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Specialized Hyphae in Mycorrhizal Fungi
Some fungi have specialized hyphae called haustoria that allow them to extract or exchange nutrients with plant hosts
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Figure 26.11
Fungal hypha
Haustorium
Plant cell
Plant cellplasmamembrane
Plantcellwall
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Mycorrhizae are mutually beneficial relationships between fungi and plant roots
Ectomycorrhizal fungi form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex
Arbuscular mycorrhizal fungi extend hyphae through the cell walls of root cells and into tubes formed by invagination of the root cell membrane
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Sexual and Asexual Reproduction
Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually
Fungi can produce spores from different types of life cycles
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Figure 26.12-1
Key
GERMINATION
SporesASEXUALREPRODUCTION
Spore-producingstructures
Mycelium
Haploid (n)
Diploid (2n)Heterokaryotic
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Figure 26.12-2
Zygote
PLASMOGAMY
Key
KARYOGAMY
GERMINATION
Spores SEXUALREPRODUCTION
ASEXUALREPRODUCTION
Heterokaryoticstage
Spore-producingstructures
Mycelium
Haploid (n)
Diploid (2n)Heterokaryotic
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Figure 26.12-3
Zygote
Spores
PLASMOGAMY
Key
KARYOGAMY
GERMINATION MEIOSISGERMINATION
Spores SEXUALREPRODUCTION
ASEXUALREPRODUCTION
Heterokaryoticstage
Spore-producingstructures
Mycelium
Haploid (n)
Diploid (2n)Heterokaryotic
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Plasmogamy is the union of cytoplasm from two haploid parent mycelia
Hours, days, or even centuries may pass before the occurrence of karyogamy, nuclear fusion
During karyogamy, the haploid nuclei fuse, producing diploid cells
The diploid phase is short-lived and undergoes meiosis, producing haploid spores
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In addition to sexual reproduction, many fungi can reproduce asexually
Molds produce haploid spores by mitosis and form visible mycelia
Single-celled yeasts reproduce asexually through cell division
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The Origin of Fungi
Fungi and animals are more closely related to each other than they are to plants or other eukaryotes
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DNA evidence suggests that Fungi are most closely related to unicellular
protists called nucleariids Animals are most closely related to unicellular
choanoflagellates This suggests that multicellularity arose separately in
animals and fungi The oldest undisputed fossils of fungi are only about
460 million years old
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Figure 26.13
50 m
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The Move to Land
Fungi were among the earliest colonizers of land and probably formed mutualistic relationships with early land plants For example, 405-million-year-old fossils of
Aglaophyton contain evidence of fossil hyphae penetrating plant cells
Video: Phlyctochytrium Spores
Video: Allomyces Zoospores
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Figure 26.14
100 nm
Zone of arbuscule-containing cells
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Figure 26.14a
100 nm
Zone of arbuscule-containing cells
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Figure 26.14b
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Molecular evidence suggests that genes required for the establishment of mycorrhizal symbiosis were present in the common ancestor to land plants
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Diversification of Fungi
Molecular analyses have helped clarify evolutionary relationships among fungal groups, although areas of uncertainty remain
There are about 100,000 known species of fungi, but there are estimated to be as many as 1.5 million species
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Figure 26.15
2.5 m
Chytrids (1,000 species)
Zygomycetes (1,000 species)
Glomeromycetes (160 species)
Ascomycetes (65,000 species)
Basidiomycetes (30,000 species)
25 mHyphae
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Chytrids (1,000 species) are found in freshwater and terrestrial habitats
Chytrids have flagellated spores and are thought to have diverged early in fungal evolution
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Figure 26.15a
Chytrids (1,000 species)
25 m
Hyphae
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Zygomycetes (1,000 species) include fast-growing molds, parasites, and commensal symbionts
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Figure 26.15b
Zygomycetes (1,000 species)
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Glomeromycetes (160 species) form arbuscular mycorrhizae with plant roots
About 80% of plant species have mutualistic relationships with glomeromycetes
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Figure 26.15c
2.5 m
Glomeromycetes (160 species)
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Ascomycetes (65,000 species) live in marine, freshwater, and terrestrial habitats
Ascomycetes produce fruiting bodies called ascocarps
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Figure 26.15d
Ascomycetes (65,000 species)
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Basidiomycetes (30,000 species) are important decomposers and ectomycorrhizal fungi
The fruiting bodies of basidiomycetes are commonly called mushrooms
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Figure 26.15e
Basidiomycetes (30,000 species)
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Concept 26.3: Early land plants radiated into a diverse set of lineages
Ancestral species gave rise to a vast diversity of modern plants
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Figure 26.16
Origin of land plants
Origin of vascular plants
Origin of extant seedplants
ANCESTRALGREENALGA
Millions of years ago (mya)500
Angiosperms
450 400 350 300 50 0
3
2
1
Gymnosperms
Mosses
Hornworts
Lycophytes (clubmosses, spikemosses, quillworts)Monilophytes (ferns,horsetails, whisk ferns)
Liverworts
Land plantsVascular plantsSeed plantsSeedlessvascularplants
Nonvascular
plants(bryophytes)
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Figure 26.16a
Origin of land plants
Origin of vascular plants
Origin of extant seedplants
ANCESTRALGREENALGA
Millions of years ago (mya)500
Angiosperms
450 400 350 300 50 0
3
2
1
Gymnosperms
Mosses
Hornworts
Lycophytes
Monilophytes
Liverworts
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Figure 26.16b
Angiosperms
Gymnosperms
Mosses
Hornworts
Lycophytes (clubmosses, spikemosses, quillworts)Monilophytes (ferns,horsetails, whisk ferns)
Liverworts Land plantsVascular plantsSeed plantsSeedlessvascularplants
Nonvascular
plants(bryophytes)
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Land plants can be informally grouped based on the presence or absence of vascular tissue
Most plants have vascular tissue for the transport of water and nutrients; these constitute the vascular plants
Nonvascular plants are commonly called bryophytes
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Bryophytes: A Collection of Early Diverging Plant Lineages
Bryophytes are represented today by three clades of small herbaceous (nonwoody) plants Liverworts Mosses Hornworts
These three clades are thought to be the earliest lineages diverged from the common ancestor of land plants
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Figure 26.UN03
AngiospermsGymnospermsSeedless vascular plantsNonvascular plants (bryophytes)
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Figure 26.17
Sporophyte
Sporophyte(a sturdyplant thattakes monthsto grow)
Gametophyte
Gametophyte
Capsule
Seta
(b) Polytrichum commune, a moss
(c) Anthoceros sp., a hornwort
(a) Plagiochila deltoidea, aliverwort
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Figure 26.17a
(a) Plagiochila deltoidea, aliverwort
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Figure 26.17b
Sporophyte(a sturdyplant thattakes monthsto grow)
Gametophyte
Capsule
Seta
(b) Polytrichum commune, a moss
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Figure 26.17c
Sporophyte
Gametophyte(c) Anthoceros sp., a hornwort
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Bryophytes are anchored to the substrate by rhizoids
The flagellated sperm produced by bryophytes must swim through a film of water to reach and fertilize the egg
In bryophytes, the gametophytes are larger and longer-living than sporophytes
The height of gametophytes is constrained by lack of vascular tissues
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Seedless Vascular Plants: The First Plants to Grow Tall Bryophytes were the prevalent vegetation during
the first 100 million years of plant evolution The earliest vascular plants date to 425–420 million
years ago Vascular tissue allowed these plants to grow tall Early vascular plants lacked seeds
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Seedless vascular plants can be divided into clades
– Lycophytes (club mosses and their relatives)
– Monilophytes (ferns and their relatives)
Video: Plant time Lapse
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Figure 26.UN04
AngiospermsGymnospermsSeedless vascular plantsNonvascular plants (bryophytes)
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Figure 26.18
(a) Diphasiastrum tristachyum, alycophyte
Strobili(conelikestructuresin whichspores areproduced)
(b) Athyrium filix-femina, amonilophyte
2.5 cm 2.5 cm
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Figure 26.18a
(a) Diphasiastrum tristachyum, alycophyte
Strobili(conelikestructuresin whichspores areproduced)
2.5 cm
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Figure 26.18b
(b) Athyrium filix-femina, amonilophyte
2.5 cm
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Life Cycles with Dominant Sporophytes
In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in familiar ferns
The gametophytes are tiny plants that grow on or below the soil surface
Flagellated sperm must swim through a film of water to reach eggs
Animation: Pine Life Cycle
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Figure 26.19
Sporophyte
Gametophyte
Example
PLANT GROUP
Mosses and othernonvascular plants
Ferns and otherseedless
vascular plants
Reduced, independent(photosynthetic andfree-living)
Reduced (usually microscopic), dependent onsurrounding sporophyte tissue for nutrition
Seed plants (gymnosperms and angiosperms)
Dominant
Dominant DominantReduced, dependenton gametophyte fornutrition
Gametophyte(n)
Gametophyte(n)
Sporophyte(2n)
Sporophyte(2n)
Sporophyte (2n) Sporophyte (2n)
Gymnosperm AngiospermMicroscopic femalegametophytes (n) insideovulate cone Microscopic female
gametophytes(n) inside these partsof flowers
Microscopicmalegametophytes(n) insidethese partsof flowersMicroscopic
malegametophytes (n)inside pollencone
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Figure 26.19a
Sporophyte
Gametophyte
Example
Mosses and othernonvascular plants
Dominant
Reduced, dependent ongametophyte for nutrition
Gametophyte(n)
Sporophyte(2n)
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Figure 26.19b
Sporophyte
Gametophyte
Example
Ferns and other seedlessvascular plants
Reduced, independent(photosynthetic and free-living)
Dominant
Gametophyte (n)
Sporophyte(2n)
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Figure 26.19c
Sporophyte
Gametophyte
Example
Reduced (usually microscopic), dependent onsurrounding sporophyte tissue for nutrition
Seed plants (gymnosperms and angiosperms)
Dominant
Sporophyte (2n)
GymnospermMicroscopic femalegametophytes (n)inside ovulatecone
Microscopic malegametophytes (n)inside pollen cone
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Figure 26.19d
Sporophyte
Gametophyte
Example
Reduced (usually microscopic), dependent onsurrounding sporophyte tissue for nutrition
Seed plants (gymnosperms and angiosperms)
Dominant
Sporophyte (2n)
Angiosperm
Microscopic female gametophytes(n) inside these partsof flowers
Microscopic malegametophytes (n) inside theseparts of flowers
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Transport in Xylem and Phloem
Vascular plants have two types of vascular tissue: xylem and phloem
Xylem conducts most of the water and minerals and includes tube-shaped cells called tracheids
Water-conducting cells are strengthened by lignin and provide structural support
Phloem consists of cells arranged in tubes that distribute sugars, amino acids, and other organic products
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Vascular tissue allowed for increased height, which provided an evolutionary advantage
Tall plants were better competitors for sunlight and could disperse spores much farther than short plants
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Evolution of Roots and Leaves
Roots are organs that anchor vascular plants They enable vascular plants to absorb water and
nutrients from the soil
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Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis
Leaves are categorized by two types Microphylls, small leaves with a single vein Megaphylls, larger, more productive leaves with a
highly branched vascular system
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Seedless vascular plants were abundant in the Carboniferous period (359–299 million years ago)
Early seed plants rose to prominence at the end of the Carboniferous period
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Concept 26.4: Seeds and pollen grains are key adaptations for life on land
Seed plants originated about 360 million years ago An adaptation called the seed allowed them to
expand into diverse terrestrial habitats A seed consists of an embryo and its food supply,
surrounded by a protective coat Mature seeds are dispersed by wind or other means
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Extant seed plants are divided into two clades Gymnosperms have “naked” seeds that are not
enclosed in chambers Angiosperms have seeds that develop inside
chambers called ovaries
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Figure 26.UN05
AngiospermsGymnospermsSeedless vascular plantsNonvascular plants (bryophytes)
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Terrestrial Adaptations in Seed Plants
In addition to seeds, the following are common to all seed plants: Reduced gametophytes Ovules Pollen
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Reduced Gametophytes
The gametophytes of seed plants are microscopic Gametophytes develop within the walls of spores
that are retained within tissues of the parent sporophyte
The parent sporophyte protects and provides nutrients to the developing gametophyte
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Ovules and Pollen
An ovule consists of an egg-producing female gametophyte surrounded by a protective layer of sporophyte tissue called the integument
Female gametophytes develop from large megaspores
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Figure 26.20-1
Immatureovulate cone
Megaspore (n)
Integument (2n)
Spore wall
Megasporangium(2n)
Pollengrain (n)Micropyle
(a) Unfertilized ovule
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Figure 26.20-2
Pollen tube
Femalegametophyte (n)
Egg nucleus(n)
Dischargedsperm nucleus(n)
Malegametophyte
Immatureovulate cone
Megaspore (n)
Integument (2n)
Spore wall
Megasporangium(2n)
Pollengrain (n)Micropyle
(a) Unfertilized ovule (b) Fertilized ovule
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Figure 26.20-3
Pollen tube
Femalegametophyte (n)
Seed coat
Sporewall
Foodsupply(n)
Embryo (2n)
Egg nucleus(n)
Dischargedsperm nucleus(n)
Malegametophyte
Immatureovulate cone
Megaspore (n)
Integument (2n)
Spore wall
Megasporangium(2n)
Pollengrain (n)Micropyle
(a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed
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Male gametophytes develop from small microspores Microspores develop into pollen grains, which
consist of a male gametophyte enclosed within the protective pollen wall
Pollination is the transfer of pollen to the part of a seed plant containing the ovules
Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals
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The Evolutionary Advantage of Seeds
A seed develops from the whole ovule A seed is a sporophyte embryo, along with its food
supply, packaged in a protective coat
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Seeds provide some evolutionary advantages over spores They may remain dormant from days to years, until
conditions are favorable for germination Seeds have a supply of stored food
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Early Seed Plants and the Rise of Gymnosperms
Fossil evidence reveals that by the late Devonian period, some plants had begun to acquire features found in seed plants but did not bear seeds
Gymnosperms appeared in the fossil record about 305 million years ago
Gymnosperms largely replaced nonvascular plants as the climate became drier toward the end of the Carboniferous period
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Gymnosperms were better suited than nonvascular plants to drier conditions due to adaptations including Seeds and pollen Thick cuticles Leaves with small surface area
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Gymnosperms are an important part of Earth’s flora For example, vast regions in northern latitudes are
covered by forests of cone-bearing gymnosperms called conifers
Video: Flower Time Lapse
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Figure 26.21
(b) Douglas fir (Pseudotsugamenziesii)
(a) Sago palm (Cycas revoluta)
(c) Creeping juniper (Juniperushorizontalis)
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Figure 26.21a
(a) Sago palm (Cycas revoluta)
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Figure 26.21b
(b) Douglas fir (Pseudotsuga menziesii)
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Figure 26.21c
(c) Creeping juniper (Juniperus horizontalis)
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The Origin and Diversification of Angiosperms
Angiosperms are seed plants with reproductive structures called flowers and fruits
They are the most widespread and diverse of all plants
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Flowers and Fruits
The flower is an angiosperm structure specialized for sexual reproduction
Many species are pollinated by insects or animals, while some species are wind-pollinated
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A flower is a specialized shoot with up to four types of modified leaves called floral organs Sepals, which enclose the flower Petals, which are brightly colored and attract
pollinators Stamens, which produce pollen Carpels, which produce ovules
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Figure 26.22
Sepal
Ovule
Petal
Style
Ovary
Stigma CarpelStamen
Filament
Anther
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A stamen consists of a stalk called a filament, with a sac called an anther where the pollen is produced
A carpel consists of an ovary at the base and a style leading up to a stigma, where pollen is received
The ovary contains one or more ovules
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Seeds develop from ovules after fertilization The ovary wall thickens and matures to form a fruit Fruits protect seeds and aid in their dispersal
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Various fruit adaptations help disperse seeds by wind, water, or animals
Fruits can function as Parachutes or propellers for wind dispersal Burrs that cling to animal fur or human clothing Food that is carried in the digestive system of animals
with seeds passing unharmed when the animal defecates
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Angiosperm Evolution
Darwin called the origin of angiosperms an “abominable mystery”
Fossil evidence and phylogenetic analysis have led to progress in solving the mystery, but we still do not fully understand the evolution of angiosperms
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Fossil evidence: Angiosperms originated at least 140 million years ago and dominated the landscape by the end of the Cretaceous period, 65 million years ago
Chinese fossils of 125-million-year-old angiosperms help us to infer traits of the angiosperm common ancestor
Archaefructus sinensis, for example, was herbaceous and may have been aquatic
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Figure 26.23
Carpel
Stamen
(a) Archaefructus sinensis, a125-million-year-old fossil
(b) Artist’s reconstruction ofArchaefructus sinensis
5 cm
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Figure 26.23a
(a) Archaefructus sinensis, a125-million-year-old fossil
5 cm
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Angiosperm phylogeny: The ancestors of angiosperms and gymnosperms diverged about 305 million years ago
Angiosperms may be closely related to Bennettitales, extinct seed plants with flowerlike structures
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Figure 26.24
Microsporangia(containmicrospores)
Ovules
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Amborella and water lilies are likely descended from two of the most ancient angiosperm lineages
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Figure 26.25
Most recent common ancestorof all living angiosperms
Magnoliids Monocots
Eudicots
Star anise
Water liliesAmborella
Amborella
Star aniseand relatives
Water lilies
Magnoliids
Monocots
Eudicots
Millions of years ago150 125 100 25 0
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Figure 26.25a
Most recent common ancestorof all living angiosperms
Amborella
Star aniseand relatives
Water lilies
Magnoliids
Monocots
Eudicots
Millions of years ago150 125 100 25 0
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Figure 26.25b
Amborella Star aniseWater lilies
Magnoliids Monocots
Eudicots
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Amborella includes only one known species, a small shrub called Amborella trichopoda
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Figure 26.25ba
Amborella
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Water lilies are found in aquatic habitats throughout the world
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Figure 26.25bb
Water lilies
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Star anise naturally occur in southeast Asia and the southeastern United States
Extant species are likely descended from ancestral populations that were separated by continental drift
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Figure 26.25bc
Star anise
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Magnoliids include magnolias, laurels, avocado, cinnamon, and black pepper plants
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Figure 26.25bd
Magnoliids
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Monocots account for more than one-quarter of angiosperm species
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Figure 26.25be
Monocots
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Eudicots account for more than two-thirds of angiosperm species
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Figure 26.25bf
Eudicots
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Concept 26.5: Land plants and fungi fundamentally changed chemical cycling and biotic interactions
The colonization of land by plants and fungi altered the physical environment and the organisms that live there
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Physical Environment and Chemical Cycling
A lichen is a symbiotic association between a photosynthetic microorganism and a fungus
Lichens are important pioneers on new rock and soil surfaces
They break down the surface, affecting the formation of soil and making it possible for plants to grow
Lichens may have helped the colonization of land by plants
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Figure 26.26 A foliose (leaflike) lichen
Crustose(encrusting) lichens
(b) Anatomy of a lichen involving an ascomycete fungusand an alga
(a) Two common lichen growth forms
Fungal hyphae Algal cell
50
m
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Figure 26.26a
A foliose (leaflike) lichen
Crustose(encrusting) lichens
(a) Two common lichen growth forms
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Figure 26.26aa
Crustose (encrusting) lichens
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Figure 26.26ab
A foliose (leaflike) lichen
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Figure 26.26b
(b) Anatomy of a lichen involving an ascomycete fungusand an alga
Fungal hyphae Algal cell
50
m
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Figure 26.26ba
Fungal hyphae Algal cell
50
m
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Plants affect the formation of soil Roots hold the soil in place Leaf litter and other decaying plant parts add
nutrients to the soil
Plants have also altered Earth’s atmosphere by releasing oxygen to the air through photosynthesis
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Plants and fungi affect the cycling of chemicals in ecosystems
Plants absorb nutrients, which are passed on to the animals that eat them
Decomposers, including fungi and bacteria, break down dead organisms and return nutrients to the physical environment
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Plants play an important role in carbon recycling
Photosynthesis removes CO2 from the atmosphere
Increased growth and accelerated photosynthesis resulted from the formation of vascular tissue and may have contributed to global cooling at the end of the Carboniferous period
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Figure 26.27
Lycophyte trees Horsetail FernLycophyte treereproductivestructures
Tree trunk coveredwith small leaves
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Biotic Interactions
Biotic interactions can benefit both species involved (mutualisms) or be beneficial to one species while harming the other (as when a parasite feeds on its host)
Plants and fungi had large effects on biotic interactions because they increased the available energy and nutrients on land
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Fungi as Mutualists and Pathogens
Mutualistic fungi absorb nutrients from a host organism and reciprocate with actions that benefit the host
Plants harbor harmless symbiotic endophytes, fungi that live inside leaves or other plant parts
Endophytes make toxins that deter herbivores and defend against pathogens
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Figure 26.28
Endophyte not present; pathogen present (E−P) Both endophyte and pathogen present (EP)
E−P E−P EP EP
15
10
5
0
Leaf
mor
talit
y (%
)
Leaf
are
a da
mag
ed (%
)
30
20
10
0
Results
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Parasitic fungi absorb nutrients from host cells, but provide no benefits in return
About 30% of known fungal species are parasites or pathogens, mostly on or in plants For example, Cryphonectria parasitica causes
chestnut blight
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Figure 26.29
(a) Corn smut on corn
(c) Ergots on rye
(b) Tar spotfunguson mapleleaves
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Figure 26.29a
(a) Corn smut on corn
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Figure 26.29b
(b) Tar spot fungus on mapleleaves
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Figure 26.29c
(c) Ergots on rye
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Plant-Animal Interactions
Animals influence the evolution of plants, and vice versa For example, animal herbivory selects for plant
defenses For example, interactions between pollinators and
flowering plants select for mutually beneficial adaptations
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Clades with bilaterally symmetrical flowers have more species than those with radially symmetrical flowers
This is likely because bilateral symmetry affects the movement of pollinators and reduces gene flow in diverging populations
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Figure 26.UN06
Bilateral symmetry
Time since divergencefrom common ancestor
Radial symmetry
Commonancestor “Bilateral” clade
“Radial” clade
Comparenumbersof species
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Angiosperms and other plant groups are being threatened by the exploding human population and its demand for space and resources
About 55,000 km2 of tropical rain forest are cleared each year
Deforestation leads to the extinction of plant, insect and other animal species
If current extinction rates continue, more than 50% of Earth’s species will be lost within the next few centuries
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Figure 26.30
(b) By 2009, much moreof this same tropicalforest had been cutdown.
(a) A satellite image from2000 shows clear-cutareas in Brazil (brown)surrounded by densetropical forest (green).
4 km
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Figure 26.30a
(a) A satellite image from2000 shows clear-cutareas in Brazil (brown)surrounded by densetropical forest (green).
4 km
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Figure 26.30b
(b) By 2009, much moreof this same tropicalforest had been cutdown.
4 km
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Figure 26.UN02a
No AM fungi
Thermal AM fungiNonthermal AM fungi
Soil treatment
Shoo
t dry
wei
ght (
g) 0.4
0.3
0.2
0.1
0.0
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Figure 26.UN02b
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Figure 26.UN02c
Root length
Soil temperature (C)
Roo
t len
gth
(cm
/g)
50
40
30
20
10Hyphal length
0
5
4
3
2
1
0
Hyp
hal l
engt
h (m
/g)
35 403020 250 45
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Figure 26.UN07
FERTILIZATIONMEIOSIS
Alternation of generations
MitosisGametophyte
Mitosis
Spore Gamete
Zygote
Mitosis
SporophyteHaploidDiploid
2n
n
n
n
n
SporesSporangium
Walled sporesin sporangia
21
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Figure 26.UN08
Sepal
Ovule
Petal
Style
Ovary
Stigma Carpel (produces ovules)Stamen
(produces pollen)
Filament
Anther
Flower anatomy
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Figure 26.UN09
Angiosperms
Gymnosperms
Mosses
Charophyte green algae
Ferns
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Figure 26.UN10