26 The Colonization of Land by Plants and Fungi

Transcription

1 CAMPBELL BIOLOGY IN FOCUS Urry Cain Wasserman Minorsky Jackson Reece 26 The Colonization of Land by Plants and Fungi Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

2 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

3 Figure 26.1 How have plants and fungi changed the world?

4 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

5 Figure 26.2 Relationships among multicellular eukaryotes Fungi Animals Charophyte algae Plants As shown in this phylogenic tree, fungi and animals are more closely related than either Group is to plants or algae.

6 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

7 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

8 Figure 26.3 Rings of cellulose-synthesizing proteins membrane proteins Found in land plants and charophyte 30 nm

9 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

10 Figure 26.4 Examples of charophytes, the closest algal relatives of land plants Chara vulgaris, a pond organism Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) 40 m

11 Figure 26.4a Chara vulgaris, a pond organism Examples of charophytes, the closest algal relatives of land plants (part 1: Chara vulgaris)

12 Figure 26.4b Examples of charophytes, the closest algal relatives of land plants (part 2: Coleochaete orbicularis) 40 m Coleochaete orbicularis, a diskshaped charophyte that also lives in ponds (LM)

13 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 CO 2, and nutrient-rich soil Land presented challenges: a scarcity of water and lack of structural support

14 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

15 Animation: Fern Life Cycle Right click slide / Select play

16 Animation: Moss Life Cycle Right click slide / Select play

17 Figure 26.5 Three possible plant kingdoms Red algae ANCESTRAL ALGA Chlorophytes Charophytes Embryophytes Plantae Streptophyta Viridiplantae

18 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

19 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

20 Figure 26.6 Alternation of generations Gametophyte (n) Mitosis n n Spore Gamete Gamete from another plant Mitosis n n Exploring alternation of generations MEIOSIS FERTILIZATION Sporophyte (2n) Zygote Mitosis 2n Multicellular, dependent embryos Key Haploid (n) Diploid (2n) Embryo Maternal tissue 10 m 2 m Wall ingrowths Placental transfer cell (blue outline)

21 Figure 26.6a Exploring alternation of generations (part 1: cycle) Alternation of generations n Mitosis n Gametophyte (n) Spore Gamete Gamete from another plant Mitosis n n MEIOSIS FERTILIZATION Zygote Sporophyte (2n) Mitosis 2n Key Haploid (n) Diploid (2n)

22 Figure 26.6b Exploring alternation of generations (part 2: multicellular, dependent embryos) Multicellular, dependent embryos Embryo Maternal tissue 10 m 2 m Wall ingrowths Placental transfer cell (blue outline)

23 Figure 26.6ba Exploring alternation of generations (part 2a: embryo, LM) Embryo Maternal tissue 10 m

24 Figure 26.6bb Exploring alternation of generations (part 2b: placental transfer cell, TEM 2 m Wall ingrowths Placental transfer cell (blue outline)

25 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

26 Walled spores produced in sporangia Sporangia are multicellular organs that produce spores Spore walls contain sporopollenin, which makes them resistant to harsh environments

27 Figure 26.7 Sporophytes and sporangia of a moss (Sphagnum) Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Sporophyte Gametophyte

28 Figure 26.7a Sporophytes and sporangia of a moss (Sphagnum) (part 1: photo) Sporangium Sporophyte Gametophyte

29 Figure 26.7b Sporophytes and sporangia of a moss (Sphagnum) (part 2: LM) Spores Sporangium Longitudinal section of Sphagnum sporangium (LM)

30 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

31 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 CO 2 and O 2 between the outside air and the plant

32 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

33 Figure 26.8 Ancient plant spores and tissue (a) Fossilized spores (b) Fossilized sporophyte tissue

34 Figure 26.8a Ancient plant spores and tissue (part 1: spores) (a) Fossilized spores

35 Figure 26.8b Ancient plant spores and tissue (part 2: tissue) (b) Fossilized sporophyte tissue

36 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

37 Animation: Fungal Reproduction Nutrition Right click slide / Select play

38 Figure 26.UN mm Cooksonia sporangium fossil (425 million years old)

39 Figure 26.9 Sporangia 25 m 2 cm Rhizoids

40 Figure 26.9a 25 m

41 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

42 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

43 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

44 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-areato-volume ratio

45 Figure Structure of a multicellular fungus Reproductive structure Hyphae Spore-producing structures 60 m Mycelium

46 Figure 26.10a Structure of a multicellular fungus (part 1: mushrooms)

47 Figure 26.10b Structure of a multicellular fungus (part 2: mycelium Mycelium

48 Figure 26.10c Structure of a multicellular fungus (part 3: mycelium, SEM) 60 m

49 Specialized Hyphae in Mycorrhizal Fungi Some fungi have specialized hyphae called haustoria that allow them to extract or exchange nutrients with plant hosts

50 Figure Haustoria of mycorrhizae Fungal hypha Plant cell wall Plant cell Haustorium Plant cell plasma membrane

51 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

52 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

53 Figure Key Generalized life cycle of fungi (step 1) Haploid (n) Heterokaryotic Diploid (2n) Spores Sporeproducing structures ASEXUAL REPRODUCTION Mycelium GERMINATION

54 Figure Key Generalized life cycle of fungi (step 2) Haploid (n) Heterokaryotic Diploid (2n) PLASMOGAMY Heterokaryotic stage Spores Sporeproducing structures ASEXUAL REPRODUCTION Mycelium SEXUAL REPRODUCTION KARYOGAMY Zygote GERMINATION

55 Figure Key Generalized life cycle of fungi (step 3) Haploid (n) Heterokaryotic Diploid (2n) PLASMOGAMY Heterokaryotic stage Spores Sporeproducing structures ASEXUAL REPRODUCTION Mycelium SEXUAL REPRODUCTION KARYOGAMY Zygote GERMINATION GERMINATION MEIOSIS Spores

56 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

57 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

58 The Origin of Fungi Fungi and animals are more closely related to each other than they are to plants or other eukaryotes

59 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

60 Figure Fossil fungal hyphae and spores from the Ordovician period (about 460 million years ago) 50 m

61 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

62 Video: Allomyces Zoospores

63 Video: Phlyctochytrium Spores

64 Figure Zone of arbusculecontaining cells An ancient symbiosis 100 nm

65 Figure 26.14a An ancient symbiosis (part 1: fossil stem cross section) Zone of arbusculecontaining cells 100 nm

66 Figure 26.14b An ancient symbiosis (part 2: arbuscule-containing cell)

67 Molecular evidence suggests that genes required for the establishment of mycorrhizal symbiosis were present in the common ancestor to land plants

68 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

69 Figure Chytrids (1,000 species) Hyphae 25 m Zygomycetes (1,000 species) Glomeromycetes (160 species) Ascomycetes (65,000 species) 2.5 m Basidiomycetes (30,000 species) Exploring fungal diversity

70 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

71 Figure 26.15a Exploring fungal diversity (part 1: chytrids) Chytrids (1,000 species) 25 m Hyphae

72 Zygomycetes (1,000 species) include fast-growing molds, parasites, and commensal symbionts

73 Figure 26.15b Exploring fungal diversity (part 2: zygomycetes) Zygomycetes (1,000 species)

74 Glomeromycetes (160 species) form arbuscular mycorrhizae with plant roots About 80% of plant species have mutualistic relationships with glomeromycetes

75 Figure 26.15c Exploring fungal diversity (part 3: glomeromycetes) Glomeromycetes (160 species) 2.5 m

76 Ascomycetes (65,000 species) live in marine, freshwater, and terrestrial habitats Ascomycetes produce fruiting bodies called ascocarps

77 Figure 26.15d Exploring fungal diversity (part 4: ascomycetes) Ascomycetes (65,000 species)

78 Basidiomycetes (30,000 species) are important decomposers and ectomycorrhizal fungi The fruiting bodies of basidiomycetes are commonly called mushrooms

79 Figure 26.15e Exploring fungal diversity (part 5: basidiomycetes) Basidiomycetes (30,000 species)

80 Concept 26.3: Early land plants radiated into a diverse set of lineages Ancestral species gave rise to a vast diversity of modern plants

81 Figure Highlights of plant evolution ANCESTRAL GREEN ALGA 1 Origin of land plants Liverworts Mosses Nonvascular plants (bryophytes) Land plants Hornworts 2 Origin of vascular plants 3 Origin of extant seed plants Lycophytes (club mosses, spike mosses, quillworts) Monilophytes (ferns, horsetails, whisk ferns) Gymnosperms Angiosperms Seedless vascular plants Seed plants Vascular plants Millions of years ago (mya)

82 Figure 26.16a Highlights of plant evolution (part 1: tree) Liverworts ANCESTRAL GREEN ALGA 1 Origin of land plants Mosses Hornworts Lycophytes 2 Origin of vascular plants Monilophytes 3 Gymnosperms Origin of extant seed plants Angiosperms Millions of years ago (mya)

83 Figure 26.16b Highlights of plant evolution (part 2: art) Liverworts Mosses Nonvascular plants (bryophytes) Land plants Hornworts Lycophytes (club mosses, spike mosses, quillworts) Monilophytes (ferns, horsetails, whisk ferns) Gymnosperms Angiosperms Seedless vascular plants Seed plants Vascular plants

84 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

85 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

86 Figure 26.UN03 nonvascular mini-tree, p. 514 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms

87 Figure Sporophyte (a) Plagiochila deltoidea, a liverwort (c) Anthoceros sp., a hornwort Gametophyte Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Bryophytes (nonvascular plants) Gametophyte (b) Polytrichum commune, a moss

88 Figure 26.17a Bryophytes (nonvascular plants) (part 1: liverwort) (a) Plagiochila deltoidea, a liverwort

89 Figure 26.17b Bryophytes (nonvascular plants) (part 2: moss) Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Gametophyte (b) Polytrichum commune, a moss

90 Figure 26.17c Bryophytes (nonvascular plants) (part 3: hornwort) Sporophyte (c) Anthoceros sp., a hornwort Gametophyte

91 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

92 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 million years ago Vascular tissue allowed these plants to grow tall Early vascular plants lacked seeds

93 Seedless vascular plants can be divided into clades Lycophytes (club mosses and their relatives) Monilophytes (ferns and their relatives)

94 Video: Plant time Lapse

95 Figure 26.UN04 seedless vascular mini-tree, p. 514 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms

96 Figure Lycophytes and monilophytes (seedless vascular plants) 2.5 cm 2.5 cm Strobili (conelike structures in which spores are produced) (a) Diphasiastrum tristachyum, a lycophyte (b) Athyrium filix-femina, a monilophyte

97 Figure 26.18a Lycophytes and monilophytes (seedless vascular plants) (part 1: lycophyte) 2.5 cm Strobili (conelike structures in which spores are produced) (a) Diphasiastrum tristachyum, a lycophyte

98 Figure 26.18b Lycophytes and monilophytes 2.5 cm (seedless vascular plants) (part 2: monilophyte) (b) Athyrium filix-femina, a monilophyte

99 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

100 Animation: Pine Life Cycle Right click slide / Select play

101 Figure Gametophyte-sporophyte relationships in different plant groups PLANT GROUP Mosses and other nonvascular plants Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) Gametophyte Dominant Reduced, independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Sporophyte Reduced, dependent on gametophyte for nutrition Dominant Dominant Sporophyte (2n) Sporophyte (2n) Gymnosperm Microscopic female gametophytes (n) inside ovulate cone Angiosperm Microscopic female gametophytes (n) inside these parts of flowers Example Gametophyte (n) Microscopic male gametophytes (n) inside pollen cone Microscopic male gametophytes (n) inside these parts of flowers Gametophyte (n) Sporophyte (2n) Sporophyte (2n)

102 Figure 26.19a Gametophyte-sporophyte relationships in different plant groups (part 1: nonvascular Gametophyte plants) Sporophyte Mosses and other nonvascular plants Dominant Reduced, dependent on gametophyte for nutrition Sporophyte (2n) Example Gametophyte (n)

103 Figure 26.19b (part 2: seedless vascular plants) Gametophyte Sporophyte Ferns and other seedless vascular plants Reduced, independent (photosynthetic and free-living) Dominant Sporophyte (2n) Example Gametophyte (n)

104 Figure 26.19c (part 3: gymnosperms) Gametophyte Sporophyte Seed plants (gymnosperms and angiosperms) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Dominant Gymnosperm Microscopic female gametophytes (n) inside ovulate cone Example Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n)

105 Figure 26.19d (part 4: angiosperms) Gametophyte Sporophyte Seed plants (gymnosperms and angiosperms) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Dominant Angiosperm Microscopic female gametophytes (n) inside these parts of flowers Example Microscopic male gametophytes (n) inside these parts of flowers Sporophyte (2n)

106 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

107 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

108 Evolution of Roots and Leaves Roots are organs that anchor vascular plants They enable vascular plants to absorb water and nutrients from the soil

109 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

110 Seedless vascular plants were abundant in the Carboniferous period ( million years ago) Early seed plants rose to prominence at the end of the Carboniferous period

111 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

112 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

113 Figure 26.UN05 seed plants mini-tree, p. 516 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms

114 Terrestrial Adaptations in Seed Plants In addition to seeds, the following are common to all seed plants: Reduced gametophytes Ovules Pollen

115 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

116 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

117 Figure From ovule to seed in a gymnosperm (step 1) Immature ovulate cone Integument (2n) Megaspore (n) Spore wall Micropyle Megasporangium (2n) Pollen grain (n) (a) Unfertilized ovule

118 Figure (step 2) Immature ovulate cone Integument (2n) Megaspore (n) Spore wall Female gametophyte (n) Egg nucleus (n) Micropyle Megasporangium (2n) Pollen grain (n) Male gametophyte Discharged sperm nucleus (n) Pollen tube (a) Unfertilized ovule (b) Fertilized ovule

119 Figure (step 3) Immature ovulate cone Integument (2n) Megaspore (n) Spore wall Female gametophyte (n) Egg nucleus (n) Seed coat Spore wall Micropyle Megasporangium (2n) Pollen grain (n) Male gametophyte Discharged sperm nucleus (n) Pollen tube Embryo (2n) Food supply (n) (a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed

120 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

121 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

122 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

123 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

124 Gymnosperms were better suited than nonvascular plants to drier conditions due to adaptations including Seeds and pollen Thick cuticles Leaves with small surface area

125 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

126 Video: Flower Time Lapse

127 Figure Examples of gymnosperms (a) Sago palm (Cycas revoluta) (b) Douglas fir (Pseudotsuga menziesii) (c) Creeping juniper (Juniperus horizontalis)

128 Figure 26.21a (part 1: sago palm) (a) Sago palm (Cycas revoluta)

129 Figure 26.21b (part 2: Douglas fir) (b) Douglas fir (Pseudotsuga menziesii)

130 Figure 26.21c (part 3: creeping juniper) (c) Creeping juniper (Juniperus horizontalis)

131 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

132 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

133 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

134 Figure The structure of an idealized flower Stigma Carpel Stamen Anther Style Filament Ovary Petal Sepal Ovule

135 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

136 Seeds develop from ovules after fertilization The ovary wall thickens and matures to form a fruit Fruits protect seeds and aid in their dispersal

137 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

138 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

139 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

140 Figure Carpel Stamen 5 cm (a) Archaefructus sinensis, a 125-million-year-old fossil An early flowering plant (b) Artist s reconstruction of Archaefructus sinensis

141 Figure 26.23a An early flowering plant (photo) 5 cm (a) Archaefructus sinensis, a 125-million-year-old fossil

142 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

143 Figure A close relative of the angiosperms? Microsporangia (contain microspores) Ovules

144 Amborella and water lilies are likely descended from two of the most ancient angiosperm lineages

145 Exploring angiosperm phylogeny Most recent common ancestor of all living angiosperms Amborella Figure Amborella Water lilies Water lilies Star anise and relatives Magnoliids Monocots Star anise Millions of years ago Eudicots Eudicots Magnoliids Monocots

146 Figure 26.25a Most recent common ancestor of all living angiosperms (part 1: tree) Amborella Water lilies Star anise and relatives Magnoliids Monocots Eudicots Millions of years ago

147 Figure 26.25b Amborella (part 2: photos) Water lilies Star anise Eudicots Magnoliids Monocots

148 Amborella includes only one known species, a small shrub called Amborella trichopoda

149 Figure 26.25ba (part 2a: Amborella) Amborella

150 Water lilies are found in aquatic habitats throughout the world

151 Figure 26.25bb (part 2b: water lilies) Water lilies

152 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

153 Figure 26.25bc Exploring angiosperm phylogeny (part 2c: star anise) Star anise

154 Magnoliids include magnolias, laurels, avocado, cinnamon, and black pepper plants

155 Figure 26.25bd Exploring angiosperm phylogeny (part 2d: magnoliids) Magnoliids

156 Monocots account for more than one-quarter of angiosperm species

157 Figure 26.25be Exploring angiosperm phylogeny (part 2e: monocots) Monocots

158 Eudicots account for more than two-thirds of angiosperm species

159 Figure 26.25bf Exploring angiosperm phylogeny (part 2f: eudicots) Eudicots

160 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

161 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

162 50 m Figure Lichens Crustose (encrusting) lichens A foliose (leaflike) lichen (a) Two common lichen growth forms Fungal hyphae Algal cell (b) Anatomy of a lichen involving an ascomycete fungus and an alga

163 Figure 26.26a Lichens (part 1: growth forms) Crustose (encrusting) lichens A foliose (leaflike) lichen (a) Two common lichen growth forms

164 Figure 26.26aa Lichens (part 1a: crustose) Crustose (encrusting) lichens

165 Figure 26.26ab Lichens (part 1b: foliose) A foliose (leaflike) lichen

166 Figure 26.26b 50 m Lichens (part 2: anatomy) Fungal hyphae Algal cell (b) Anatomy of a lichen involving an ascomycete fungus and an alga

167 Figure 26.26ba 50 m Lichens (part 2a: anatomy micrograph) Fungal hyphae Algal cell

168 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

169 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

170 Plants play an important role in carbon recycling Photosynthesis removes CO 2 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

171 Figure Fern Artist s conception of a Carboniferous forest based on fossil evidence Lycophyte trees Horsetail Tree trunk covered with small leaves Lycophyte tree reproductive structures

172 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

173 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

174 Figure Leaf mortality (%) Leaf area damaged (%) Results Endophyte not present; pathogen present (E P ) Both endophyte and pathogen present (E P ) E P E P E P E P

175 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

176 Figure Examples of fungal diseases of plants (b) Tar spot fungus on maple leaves (a) Corn smut on corn (c) Ergots on rye

177 Figure 26.29a (part 1: corn smut) (a) Corn smut on corn

178 Figure 26.29b (part 2: tar spot fungus) (b) Tar spot fungus on maple leaves

179 Figure 26.29c (part 3: ergots on rye) (c) Ergots on rye

180 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

181 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

182 Figure 26.UN06 Bilateral symmetry Radial symmetry Common ancestor Time since divergence from common ancestor Bilateral clade Radial clade Compare numbers of species

183 Angiosperms and other plant groups are being threatened by the exploding human population and its demand for space and resources About 55,000 km 2 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

184 Figure km (a) A satellite image from 2000 shows clear-cut areas in Brazil (brown) surrounded by dense tropical forest (green). (b) By 2009, much more of this same tropical forest had been cut down.

185 Figure 26.30a 4 km (a) A satellite image from 2000 shows clear-cut areas in Brazil (brown) surrounded by dense tropical forest (green).

186 Figure 26.30b 4 km (b) By 2009, much more of this same tropical forest had been cut down.

187 Figure 26.UN02a Shoot dry weight (g) No AM fungi Nonthermal AM fungi Thermal AM fungi Soil treatment

188 Figure 26.UN02b

189 Figure 26.UN02c Root length (cm/g) Hyphal length (m/g) Root length Hyphal length Soil temperature ( C)

190 Figure 26.UN07 n Gametophyte Mitosis Mitosis n n Spore Gamete n MEIOSIS FERTILIZATION Sporangium Spores 2n Zygote Sporophyte Mitosis Haploid Diploid 1 Alternation of generations 2 Walled spores in sporangia

191 Figure 26.UN08 Stamen (produces pollen) Anther Filament Stigma Carpel (produces ovules) Style Ovary Petal Sepal Ovule Flower anatomy

192 Figure 26.UN09 Charophyte green algae Mosses Ferns Gymnosperms Angiosperms

193 Figure 26.UN10