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Plant Diversity I: How Plants Colonized Land
Chapter 29 Plant Diversity I: How Plants Colonized Land
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Overview: The Greening of Earth
Around 500 million years ago, small plants, fungi, and animals emerged on land Now approximately 290,000 species Have terrestrial ancestors Do not include protists Supply oxygen Ultimate source of food for land animals © 2011 Pearson Education, Inc.
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Figure 29.1 Figure 29.1 How did plants change the world? 1 m
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Concept 29.1: Land plants evolved from green algae
called charophytes share four key traits with only charophytes Rings of cellulose-synthesizing complexes Peroxisome enzymes – minimize loss of organic products during photorespiration Structure of flagellated sperm Formation of a phragmoplast – precusor to cell plate Comparison of nuclear and chloroplast genes © 2011 Pearson Education, Inc.
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1 m Chara species, a pond organism 5 mm
Figure 29.3 Chara species, a pond organism 5 mm Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) Figure 29.3 Examples of charophytes, the closest algal relatives of land plants. 40 m 1 m
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Adaptations Enabling the Move to Land
sporopollenin prevents exposed zygotes from drying out; also found in plant spore walls provided 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 © 2011 Pearson Education, Inc.
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Derived Traits of Plants
Four key traits appear in nearly all land plants but are absent in the charophytes 1. Alternation of generations and multicellular, dependent embryos 2. Walled spores produced in sporangia 3. Multicellular gametangia 4. Apical meristems © 2011 Pearson Education, Inc.
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Alternation of Generations and Multicellular, Dependent Embryos
gametophyte - haploid and produces haploid gametes by mitosis Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis © 2011 Pearson Education, Inc.
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1 m Key Gamete from another plant Haploid (n) Gametophyte (n)
Figure 29.5a Key Gamete from another plant Gametophyte (n) Haploid (n) Diploid (2n) Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION 2n Zygote Figure 29.5 Exploring: Derived Traits of Land Plants Mitosis Sporophyte (2n) Alternation of generations 1 m
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The Flow Sporophyte (meiosis)spores (mitosis) to produce gametophytereleases gametes produced by mitosisfertiliztion produces zygotemitosis develops a sporophyte
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Walled Spores Produced in Sporangia
The sporophyte produces spores in organs called sporangia Diploid cells called sporocytes undergo meiosis to generate haploid spores Spore walls contain sporopollenin, which makes them resistant to harsh environments © 2011 Pearson Education, Inc.
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Figure 29.5c Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Figure 29.5 Exploring: Derived Traits of Land Plants Sporophyte Gametophyte 1 m Sporophytes and sporangia of Sphagnum (a moss)
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Multicellular Gametangia
Gametes are produced within organs called gametangia Female gametangia, - archegonia, produce eggs and are the site of fertilization Male gametangia - antheridia, produce and release sperm © 2011 Pearson Education, Inc.
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1 m Female gametophyte Archegonia, each with an egg (yellow)
Figure 29.5d Female gametophyte Archegonia, each with an egg (yellow) Antheridia (brown), containing sperm Figure 29.5 Exploring: Derived Traits of Land Plants Male gametophyte Archegonia and antheridia of Marchantia (a liverwort) 1 m
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Plant growth occurs at this structural site
Apical Meristems Plant growth occurs at this structural site Cells from the apical meristems differentiate into various tissues © 2011 Pearson Education, Inc.
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1 m Apical meristem of shoot Developing leaves
Figure 29.5e Apical meristem of shoot Developing leaves Apical meristems of plant roots and shoots Figure 29.5 Exploring: Derived Traits of Land Plants Apical meristem of root Root Shoot 100 m 1 m 100 m
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Additional derived traits include
a. Cuticle, a waxy covering of the epidermis b. Mycorrhizae, symbiotic associations between fungi and land plants that may have helped plants without true roots to obtain nutrients c. Secondary compounds that deter herbivores and parasites © 2011 Pearson Education, Inc.
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The Origin and Diversification of Plants
Fossil evidence indicates that plants were on land at least 475 million years ago Fossilized spores and tissues have been extracted from 475-million-year-old rocks © 2011 Pearson Education, Inc.
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1 m (a) Fossilized spores Fossilized sporophyte tissue (b)
Figure 29.6 (a) Fossilized spores Figure 29.6 Ancient plant spores and tissue (colorized SEMs). Fossilized sporophyte tissue (b) 1 m
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1 m Figure 29.7 1 Origin of land plants (about 475 mya) 2
Origin of vascular plants (about 425 mya) 3 Origin of extant seed plants (about 305 mya) Liverworts Nonvascular plants (bryophytes) ANCESTRAL GREEN ALGA Land plants 1 Mosses Hornworts Lycophytes (club mosses, spike mosses, quillworts) Seedless vascular plants 2 Pterophytes (ferns, horsetails, whisk ferns) Vascular plants Figure 29.7 Highlights of plant evolution. Gymnosperms 3 Seed plants Angiosperms 500 450 400 350 300 50 Millions of years ago (mya) 1 m
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Most plants have vascular tissue; these constitute the vascular plants
Land plants can be informally grouped based on the presence or absence of vascular tissue Most plants have vascular tissue; these constitute the vascular plants Nonvascular plants are commonly called bryophytes © 2011 Pearson Education, Inc.
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A seed - an embryo and nutrients surrounded by a protective coat
Seed plants: Gymnosperms, the “naked seed” plants, including the conifers Angiosperms, the flowering plants © 2011 Pearson Education, Inc.
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Table 29. 1 Table 29.1 Ten Phyla of Extant Plants 1 m
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Concept 29.2:Dominant gametophyte stage
Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants Liverworts Hornworts Mosses © 2011 Pearson Education, Inc.
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1 m “Bud” Male gametophyte (n) Key Haploid (n) Protonemata (n)
Figure “Bud” Male gametophyte (n) Key Haploid (n) Protonemata (n) Diploid (2n) “Bud” Spores Gametophore Spore dispersal Female gametophyte (n) Rhizoid Peristome Sporangium Seta Figure 29.8 The life cycle of a moss. MEIOSIS Capsule (sporangium) Mature sporophytes Foot 2 mm 1 m Capsule with peristome (LM) Female gametophytes
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1 m Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n)
Figure Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n) Protonemata (n) Diploid (2n) “Bud” Egg Spores Gametophore Spore dispersal Archegonia Female gametophyte (n) Rhizoid Peristome FERTILIZATION Sporangium Seta Figure 29.8 The life cycle of a moss. (within archegonium) MEIOSIS Capsule (sporangium) Mature sporophytes Foot 2 mm 1 m Capsule with peristome (LM) Female gametophytes
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1 m Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n)
Figure Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n) Protonemata (n) Diploid (2n) “Bud” Egg Spores Gametophore Spore dispersal Archegonia Female gametophyte (n) Rhizoid Peristome FERTILIZATION Sporangium Seta Figure 29.8 The life cycle of a moss. Zygote (2n) (within archegonium) MEIOSIS Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium Young sporophyte (2n) 2 mm 1 m Capsule with peristome (LM) Female gametophytes
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Capsule with peristome (LM)
Figure 29.8a Figure 29.8 The life cycle of a moss. 2 mm 1 m Capsule with peristome (LM)
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Animation: Moss Life Cycle
© 2011 Pearson Education, Inc.
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1 m Gametophore of female gametophyte Thallus Sporophyte Foot Seta
Figure 29.9a Gametophore of female gametophyte Thallus Sporophyte Foot Seta Capsule (sporangium) Marchantia polymorpha, a “thalloid” liverwort Figure 29.9 Exploring: Bryophyte Diversity 500 m Marchantia sporophyte (LM) Plagiochila deltoidea, a “leafy” liverwort 1 m
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1 m An Anthoceros hornwort species Sporophyte Gametophyte
Figure 29.9b An Anthoceros hornwort species Sporophyte Figure 29.9 Exploring: Bryophyte Diversity Gametophyte 1 m
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1 m Polytrichum commune, hairy-cap moss
Figure 29.9c Polytrichum commune, hairy-cap moss Sporophyte (a sturdy plant that takes months to grow) Capsule Seta Figure 29.9 Exploring: Bryophyte Diversity Gametophyte 1 m
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The Ecological and Economic Importance of Mosses
Mosses are capable of inhabiting diverse and sometimes extreme environments, but are especially common in moist forests and wetlands Some mosses might help retain nitrogen in the soil © 2011 Pearson Education, Inc.
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Peat can be used as a source of fuel
Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Peat can be used as a source of fuel Sphagnum is an important global reservoir of organic carbon Overharvesting of Sphagnum and/or a drop in water level in peatlands could release stored CO2 to the atmosphere © 2011 Pearson Education, Inc.
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1 m Peat being harvested from a peatland (a)
Figure 29.11 Figure Sphagnum, or peat moss: a bryophyte with economic, ecological, and archaeological significance. Peat being harvested from a peatland (a) “Tollund Man,” a bog mummy dating from 405–100 B.C.E. (b) 1 m
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Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall
Vascular plants began to diversify during the Devonian and Carboniferous periods Vascular tissue allowed these plants to grow tall Seedless vascular plants have flagellated sperm and are usually restricted to moist environments © 2011 Pearson Education, Inc.
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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 Animation: Fern Life Cycle © 2011 Pearson Education, Inc.
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1 m Key Haploid (n) Diploid (2n) Spore dispersal MEIOSIS Sporangium
Figure Key Haploid (n) Diploid (2n) Spore dispersal MEIOSIS Sporangium Mature sporophyte (2n) Sporangium Sorus Figure The life cycle of a fern. Fiddlehead (young leaf) 1 m
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1 m Key Haploid (n) Diploid (2n) Spore (n) Antheridium
Figure Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Rhizoid Underside of mature gametophyte (n) Sporangium Sperm Archegonium Mature sporophyte (2n) Egg Sporangium FERTILIZATION Sorus Figure The life cycle of a fern. Fiddlehead (young leaf) 1 m
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1 m Key Haploid (n) Diploid (2n) Spore (n) Antheridium
Figure Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Rhizoid Underside of mature gametophyte (n) Sporangium Sperm Archegonium Mature sporophyte (2n) Egg New sporophyte Sporangium Zygote (2n) FERTILIZATION Sorus Figure The life cycle of a fern. Gametophyte Fiddlehead (young leaf) 1 m
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Vascular Plants 1. Xylem conducts most of the water and minerals and includes dead cells called tracheids Water-conducting cells are strengthened by lignin and provide structural support 2. Phloem consists of living cells and distributes sugars, amino acids, and other organic products Vascular tissue allowed for increased height, which provided an evolutionary advantage © 2011 Pearson Education, Inc.
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Roots are organs that anchor vascular plants
Evolution of Roots Roots are organs that anchor vascular plants They enable vascular plants to absorb water and nutrients from the soil Roots may have evolved from subterranean stems © 2011 Pearson Education, Inc.
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Evolution of Leaves Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis © 2011 Pearson Education, Inc.
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All seed plants and some seedless vascular plants are heterosporous
Most seedless vascular plants are homosporous, producing one type of spore that develops into a bisexual gametophyte All seed plants and some seedless vascular plants are heterosporous Heterosporous species produce megaspores, which give rise to female gametophytes, and microspores, which give rise to male gametophytes © 2011 Pearson Education, Inc.
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1 m 2.5 cm Isoetes gunnii, a quillwort
Figure 29.15a 2.5 cm Isoetes gunnii, a quillwort Strobili (clusters of sporophylls) Selaginella moellendorffii, a spike moss Figure Exploring: Seedless Vascular Plant Diversity 1 cm 1 m Diphasiastrum tristachyum, a club moss
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1 m Athyrium filix-femina, lady fern
Figure 29.15b Athyrium filix-femina, lady fern Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem 25 cm 1.5 cm Psilotum nudum, a whisk fern Figure Exploring: Seedless Vascular Plant Diversity 1 m 4 cm
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The Significance of Seedless Vascular Plants
The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Devonian and Carboniferous, forming the first forests Increased growth and photosynthesis removed CO2 from the atmosphere and may have contributed to global cooling at the end of the Carboniferous period The decaying plants of these Carboniferous forests eventually became coal © 2011 Pearson Education, Inc.
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1 m Tree trunk covered with small leaves
Figure 29.16 Tree trunk covered with small leaves Lycophyte tree reproductive structures Fern Lycophyte trees Horsetail Figure Artist’s conception of a Carboniferous forest based on fossil evidence. 1 m
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