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Create a timeline with the following events: a. b. c. d. e. f. g. h. Earth is born First life Multicellularity Colonization of land First vascular plants First insects Dinosaurs Flowering plants Create a timeline with the following events: a. b. c. d. e. f. g. h. Earth is born 4.6 bya First life 3.8 bya Multicellularity 1 bya Colonization of land 500 mya (or 1.2 bya) First vascular plants 425 mya First insects 400 mya Dinosaurs 300 mya Flowering plants 130 mya LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 29 Plant Diversity I: How Plants Colonized Land Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Guiding questions: • Why did land plants come to be? • What challenges did it pose? • Name the 4 primary clades of all plants. – Derived traits of them collectively • Especially alternation of generations – Ancestral traits of them collectively • What are the derived characters unique to seedless plants? – Non-vascular (mosses) – Vascular (ferns) Concept 29.1: Land plants evolved from green algae • Green algae called charophytes are the closest relatives of land plants – Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes © 2011 Pearson Education, Inc. 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 • Why move to land? • What challenges did the move pose? © 2011 Pearson Education, Inc. Figure 29.4 Red algae Chlorophytes 1 m Plantae Embryophytes Streptophyta Charophytes Viridiplantae ANCESTRAL ALGA Derived Traits of Plants • Four key traits appear in nearly all land plants but are absent in the charophytes 1. 2. 3. 4. Alternation of generations Walled spores produced in sporangia Multicellular gametangia Apical meristems © 2011 Pearson Education, Inc. 1. Alternation of Generations and Multicellular, Dependent Embryos • Plants alternate between two multicellular stages, a reproductive cycle called 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 © 2011 Pearson Education, Inc. • The 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 © 2011 Pearson Education, Inc. Figure 29.5a Gametophyte (n) Mitosis n Gamete from another plant Mitosis n FERTILIZATION 2n Sporophyte (2n) Haploid (n) Diploid (2n) n Spore Gamete n MEIOSIS Key Zygote Mitosis Alternation of generations 1 m 2. 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. Figure 29.5c Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Sporophyte Gametophyte 1 m Sporophytes and sporangia of Sphagnum (a moss) 3. Multicellular Gametangia • Gametes are produced within organs called gametangia • Female gametangia, called archegonia, produce eggs and are the site of fertilization • Male gametangia, called antheridia, produce and release sperm © 2011 Pearson Education, Inc. Figure 29.5d Female gametophyte Archegonia, each with an egg (yellow) Antheridia (brown), containing sperm Male gametophyte Archegonia and antheridia of Marchantia (a liverwort) 1 m 4. Apical Meristems • Plants sustain continual growth in their apical meristems • Cells from the apical meristems differentiate into various tissues © 2011 Pearson Education, Inc. Figure 29.5e Apical meristem of shoot Developing leaves Apical meristems of plant roots and shoots Apical meristem of root Root 100 m Shoot 1 m 100 m • Additional derived traits include – Cuticle, a waxy covering of the epidermis – Mycorrhizae, symbiotic associations between fungi and land plants that may have helped plants without true roots to obtain nutrients – Secondary compounds that deter herbivores and parasites – Very useful to humans, too © 2011 Pearson Education, Inc. 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) Mosses Land plants ANCESTRAL 1 GREEN ALGA Nonvascular plants (bryophytes) Liverworts Hornworts Pterophytes (ferns, horsetails, whisk ferns) 3 Angiosperms 500 450 400 350 300 Millions of years ago (mya) 50 0 1 m Know plant types, and key distinguishing elements Seed plants Gymnosperms Vascular plants 2 Seedless vascular plants Lycophytes (club mosses, spike mosses, quillworts) • Seedless plants can be divided into clades – Bryophytes (non-vascular, e.g. mosses and their relatives) – Lycophytes and Pterophytes (vascular, e.g. club mossess, ferns and their relatives) – Seedless vascular plants are paraphyletic, and are of the same level of biological organization, or grade © 2011 Pearson Education, Inc. • A seed is an embryo and nutrients surrounded by a protective coat • Seed plants form a clade and can be divided into further clades – Gymnosperms, the “naked seed” plants, including the conifers – Angiosperms, the flowering plants Table 29. 1 1 m Concept 29.2: Mosses and other nonvascular plants have life cycles dominated by gametophytes • Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants – Liverworts, phylum Hepatophyta – Hornworts, phylum Anthocerophyta – Mosses, phylum Bryophyta • Bryophyte refers to all nonvascular plants, whereas Bryophyta refers only to the phylum of mosses © 2011 Pearson Education, Inc. Figure 29.UN01 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms 1 m Bryophyte Gametophytes • In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes • Sporophytes are typically present only part of the time © 2011 Pearson Education, Inc. Figure 29.8-1 “Bud” Key Haploid (n) Diploid (2n) Protonemata (n) “Bud” Spores Male gametophyte (n) Gametophore Spore dispersal Female gametophyte (n) Peristome Sporangium MEIOSIS Mature sporophytes Rhizoid Seta Capsule (sporangium) 2 mm Foot Capsule with peristome (LM) 1 m Female gametophytes Figure 29.8-2 “Bud” Key Haploid (n) Diploid (2n) Protonemata (n) “Bud” Sperm Antheridia Male gametophyte (n) Egg Spores Gametophore Spore dispersal Female gametophyte (n) Peristome Sporangium MEIOSIS Mature sporophytes Archegonia Rhizoid FERTILIZATION (within archegonium) Seta Capsule (sporangium) 2 mm Foot Capsule with peristome (LM) 1 m Female gametophytes Figure 29.8-3 “Bud” Key Haploid (n) Diploid (2n) Protonemata (n) “Bud” Antheridia Male gametophyte (n) Sperm Egg Spores Gametophore Spore dispersal Female gametophyte (n) Peristome Sporangium MEIOSIS Mature sporophytes Archegonia Rhizoid FERTILIZATION Zygote (within archegonium) (2n) Seta Capsule (sporangium) Foot Embryo 2 mm Archegonium Capsule with peristome (LM) Young sporophyte (2n) Female gametophytes 1 m Animation: Moss Life Cycle Right-click slide / select “Play” © 2011 Pearson Education, Inc. Bryophyte Sporophytes • Bryophyte sporophytes grow out of archegonia, and are the smallest and simplest sporophytes of all extant plant groups • A sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome • Hornwort and moss sporophytes have stomata for gas exchange; liverworts do not © 2011 Pearson Education, Inc. Figure 29.9a Thallus Gametophore of female gametophyte Sporophyte Foot Seta Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM) 500 m Capsule (sporangium) Plagiochila deltoidea, a “leafy” liverwort 1 m Figure 29.9b An Anthoceros hornwort species Sporophyte Gametophyte 1 m Figure 29.9c Polytrichum commune, hairy-cap moss Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Gametophyte 1 m Annual nitrogen loss (kg/ha) Can bryophytes reduce the rate at which key nutrients are lost from soils? RESULTS 6 5 4 3 2 1 0 With moss Without moss 1 m Figure 29.11 (a) Peat being harvested from a peatland (b) “Tollund Man,” a bog mummy dating from 405–100 B.C.E. 1 m Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall • Why bother striving for being tall? • What new feature allowed for height? © 2011 Pearson Education, Inc. Figure 29.UN03 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms 1 m Derived Traits of Vascular Plants • Living vascular plants are characterized by 1. Life cycles with dominant sporophytes 2. Vascular tissues called xylem and phloem 3. Well-developed roots and leaves © 2011 Pearson Education, Inc. Figure 29.12 Sporangia 1 m 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 • Seedless vascular plants have flagellated sperm and are usually restricted to moist environments © 2011 Pearson Education, Inc. Figure 29.13-3 Key Haploid (n) Diploid (2n) MEIOSIS Spore dispersal Spore (n) Rhizoid Underside of mature gametophyte (n) Sporangium Sporangium Antheridium Young gametophyte Mature sporophyte (2n) Sorus New sporophyte Sperm Archegonium Egg Zygote (2n) Gametophyte Fiddlehead (young leaf) 1 m FERTILIZATION Animation: Fern Life Cycle Right-click slide / select “Play” © 2011 Pearson Education, Inc. 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 dead cells called tracheids – Water-conducting cells are strengthened by lignin and provide structural support – Phloem consists of living cells and distributes sugars, amino acids, and other organic products © 2011 Pearson Education, Inc. Evolution of Roots and Leaves • Roots were originally underground stems • 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, leaves with a single vein Megaphylls, leaves with a highly branched vascular system • According to one model of evolution, microphylls evolved as outgrowths of stems • Megaphylls may have evolved as webbing between flattened branches © 2011 Pearson Education, Inc. Figure 29.14 Overtopping growth Vascular tissue Sporangia Microphyll Megaphyll Other stems become reduced and flattened. (a) Microphylls (b) Megaphylls 1 m Webbing develops. Seedless plant diversity 2.5 cm 1 cm Selaginella moellendorffii, a spike moss Isoetes gunnii, a quillwort Strobili (clusters of sporophylls) Diphasiastrum 1 m tristachyum, a club moss Vascular plant diversity Equisetum arvense, field horsetail Athyrium filix-femina, lady fern Vegetative stem 1.5 cm 25 cm Strobilus on fertile stem 4 cm Psilotum nudum, a whisk fern 1 m Applying ideas Fern Lycophyte trees Horsetail Tree trunk covered with small leaves Lycophyte tree reproductive structures How would the first large plants have affected global climate? Processing the big points (flip your paper over) • Can you name the derived traits of the colonizing land plants (mosses)? • Can you name the derived traits of vascular, seedless plants (ferns)? • What ancestral traits do plants share with the protists from which they split? Processing the big points • Can you name the derived traits of the colonizing land plants (mosses)? 1. 2. 3. 4. Alternation of generations Walled spores produced in sporangia Multicellular gametangia Apical meristems As well as: cuticles, secondary compounds, symbioses • Can you name the derived traits of vascular, seedless plants (ferns)? • What ancestral traits do plants share with the protists from which they split? Processing the big points • Can you name the derived traits of the colonizing land plants (mosses)? • Can you name the derived traits of vascular, seedless plants (ferns)? 1. Life cycles with dominant sporophytes 2. Vascular tissues called xylem and phloem 3. Well-developed roots and leaves • What ancestral traits do plants share with the protists from which they split? Processing the big points • Can you name the derived traits of the colonizing land plants (mosses)? • Can you name the derived traits of vascular, seedless plants (ferns)? • What ancestral traits do plants share with the protists from which they split? – Chloroplasts – All eukaryotic cell functions and organelles Figure 29: summary of common traits Gametophyte Mitosis Mitosis n n n Spore n Gamete MEIOSIS Apical meristem of shoot Developing leaves FERTILIZATION 2n Zygote Haploid Diploid Mitosis Sporophyte 1 Alternation of generations Archegonium with egg 2 Apical meristems Antheridium with sperm Sporangium Spores 1 m 3 Multicellular gametangia 4 Walled spores in sporangia