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Chapter 29 Plant Diversity I: How Plants Colonized Land PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Morphological and Molecular Evidence • Land plants share four key traits only with charophytes: – Rose-shaped complexes for cellulose synthesis – Peroxisome enzymes – Structure of flagellated sperm – Formation of a phragmoplast Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-3 Examples of charophytes, the closest algal relatives of land plants 5 mm Chara species, a pond organism Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) 40 µm Adaptations Enabling the Move to Land • In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out • Land presented challenges: a scarcity of water and lack of structural support Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-4 Three possible “plant” kingdoms Red algae Chlorophytes 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: – Alternation of generations (with multicellular, dependent embryos) – Walled spores produced in sporangia – Multicellular gametangia – Apical meristems • Additional derived traits such as a cuticle and secondary compounds evolved in many plant species • Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Alternation of Generations and Multicellular, Dependent Embryos • Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations • Gametophyte - haploid and produces haploid gametes by mitosis • Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis • The diploid embryo is retained within the tissue of the female gametophyte • Placental transfer cells transfer nutrients from parent to embryo • Land plants are called embryophytes because of the dependency of the embryo on the parent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-5a Gametophyte (n) Mitosis n n Spore Gamete from another plant Mitosis n n Gamete MEIOSIS FERTILIZATION 2n Mitosis Sporophyte (2n) Alternation of generations Zygote Walled Spores Produced in Sporangia • Sporangia – organ in the sporophyte that produces spores • Sporocytes (2n) undergo meiosis to generate haploid spores • Spore walls contain sporopollenin, which makes them resistant to harsh environments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-5c Derived traits of land plants Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Sporophyte Gametophyte Sporophytes and sporangia of Sphagnum (a moss) Multicellular Gametangia • Gametes are produced within organs called gametangia • Female gametangia - archegonia • Male gametangia - antheridia Apical Meristems • Plants sustain continual growth in their apical meristems • Cells from the apical meristems differentiate into various tissues Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-5d Female gametophyte Archegonium with egg Antheridium with sperm Male gametophyte Archegonia and antheridia of Marchantia (a liverwort) Fig. 29-5e Apical meristem of shoot Shoot Developing leaves 100 µm Apical meristems Apical meristem of root Root 100 µm • Most plants have vascular tissue - vascular plants • Nonvascular plants aka bryophytes • Seedless vascular plants are paraphyletic – Lycophytes (club mosses and their relatives) – Pterophytes (ferns and their relatives) • Seed - embryo and nutrients surrounded by a protective coat – Gymnosperms, the “naked seed” plants, including the conifers – Angiosperms, the flowering plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-7 1 Origin of land plants (about 475 mya) 2 Origin of vascular plants (about 420 mya) 3 Origin of extant seed plants (about 305 mya) Hornworts 1 Mosses Pterophytes (ferns, horsetails, whisk ferns) 3 Angiosperms 450 400 350 300 Millions of years ago (mya) 50 0 Seed plants Gymnosperms Vascular plants 2 Seedless vascular plants Lycophytes (club mosses, spike mosses, quillworts) 500 Land plants ANCESTRAL GREEN ALGA Nonvascular plants (bryophytes) Liverworts 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, phy. Bryophyta, are most related to vascular plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte Gametophytes • Gametophytes are larger and longer-living than sporophytes • Sporophytes are typically present only part of the time • Spores germinates into a gametophyte composed of a protonema and gamete-producing gametophore • Rhizoids anchor gametophytes to substrate • Mature gametophytes produce flagellated sperm in antheridia and an egg in each archegonium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-8-3 Raindrop Sperm “Bud” Key Haploid (n) Diploid (2n) Protonemata (n) Antheridia Male gametophyte (n) “Bud” Egg Spores Gametophore Female Archegonia gametophyte (n) Spore dispersal Rhizoid Peristome FERTILIZATION Sporangium MEIOSIS Mature sporophytes Seta Capsule (sporangium) Foot (within archegonium) Zygote (2n) Embryo 2 mm Archegonium Capsule with peristome (SEM) Young sporophyte (2n) Female gametophytes 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, aka capsule, which discharges spores through a peristome • Hornwort and moss sporophytes have stomata for gas exchange Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9a Thallus Gametophore of female gametophyte Sporophyte Foot Seta Marchantia sporophyte (LM) 500 µm Marchantia polymorpha, a “thalloid” liverwort Capsule (sporangium) Fig. 29-9c An Anthoceros hornwort species Sporophyte Gametophyte Fig. 29-9d Polytrichum commune, hairy-cap moss Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Gametophyte Transport in Xylem and Phloem (AKA vascular tissue) • Living vascular plants are characterized by: • Life cycles with dominant sporophytes • Vascular tissues called xylem and phloem • Well-developed roots and leaves • Xylem conducts most of the water and minerals and includes dead cells called tracheids • Phloem consists of living cells and distributes sugars, amino acids, and other organic products • Water-conducting cells are strengthened by lignin and provide structural support • Increased height was an evolutionary advantage Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Roots and Leaves • Roots - organs that anchor vascular plants and enable them to absorb water and nutrients from the soil. • Leaves - organs that increase the surface area of vascular plants (capturing more solar energy) • Microphylls, leaves with a single vein • Megaphylls, leaves with a highly branched vascular system • Sporophylls - modified leaves with sporangia • Sori -clusters of sporangia on the undersides of sporophylls • Strobili - cone-like structures formed from groups of sporophylls Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-UN3 Homosporous spore production (Most seedless vascular plants) Sporangium on sporophyll Single type of spore Typically a bisexual gametophyte Eggs Sperm Heterosporous spore production (All seed plants & some Megasporangium on megasporophyll Megaspore Microsporangium on microsporophyll Microspore seedless vascular plants) Female Eggs gametophyte Male gametophyte Sperm Fig. 29-15a Seedless vascular plant diversity Lycophytes (Phylum Lycophyta) 2.5 cm Isoetes Strobili (clusters of gunnii, a quillwort sporophylls) 1 cm Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss Fig. 29-15e Seedless vascular plant diversity Pterophytes (Phylum Pterophyta) Athyrium filix-femina, lady fern Equisetum arvense, field horsetail Psilotum nudum, a whisk fern Vegetative stem 2.5 cm 1.5 cm 25 cm Strobilus on fertile stem Fig. 29-UN4 Gametophyte Mitosis Mitosis n n Spore Gamete MEIOSIS Apical meristem of shoot Developing leaves n n FERTILIZATION Zygote 2n Mitosis Haploid Sporophyte Diploid 1 Alternation of generations Archegonium with egg 2 Apical meristems Antheridium with sperm 3 Multicellular gametangia Sporangium Spores 4 Walled spores in sporangia