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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 Overview: The Greening of Earth • Looking at a lush landscape, it is difficult to imagine the land without any plants or other organisms • For more than the first 3 billion years of Earth’s history, the terrestrial surface was lifeless • Since colonizing land, plants have diversified into roughly 290,000 living species • Plants supply oxygen and are the ultimate source of most food eaten by land animals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.1: Land plants evolved from green algae • Green algae called charophytes are the closest relatives of land plants • Morphological and Molecular Evidence • Many characteristics of land plants also appear in a variety of algal clades, mainly algae • However, 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 • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-3 5 mm Chara species, a pond organism Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) 40 µm Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Adaptations Enabling the Move to Land • In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out • The movement onto land by charophyte ancestors 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 • The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants • Some biologists think the plant kingdom should be expanded to include some or all green algae • Until this debate is resolved, we will retain the embryophyte definition of kingdom Plantae Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-4 Red algae Chlorophytes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gametophyte (n) Fig. 29-5a produces haploid gametes by mitosis Mitosis Mitosis n sporophyte produces haploid spores n Spore 2 gametes from different plants form a zygote Gamete FERTILIZATION MEIOSIS 2n zygote develops into a multicellular diploid sporophyte Mitosis Sporophyte (2n) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Alternation of Generations • 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 embryo wall ingrowths placental transfer cell (blue outline) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings maternal tissue 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 sporangium containing spores sporophyte gametophyte Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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, are the site of sperm production and release femalegemetophyte Archegonium with egg Antheridium with sperm male gametophyte Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Apical Meristems • Plants sustain continual growth in their apical meristems • Cells from the apical meristems differentiate into various tissues apical meristem developing leaves shoot Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings root Other Characteristics • epidermis in many species has a covering named cuticle which acts as waterproof preventing desiccation and protects against microbal infections • secondary compounds are produced in secondary metabolic pathways; examples are terpenes, alkaloids, tannins that have bitter taste, strong odors, toxic effect on consumers and pathogens Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 fossilized spores with more than one grain fossilized sporophyte tissue with spores embebed in it Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Those ancestral species gave rise to a vast diversity of modern 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Seedless vascular plants can be divided into clades – Lycophytes (club mosses and their relatives) – Pterophytes (ferns and their relatives) • Seedless vascular plants are paraphyletic, and are of the same level of biological organization, or grade Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 29-1 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-7 origin of land plants (about 475 mya) origin of vascular plants (about 420 mya) origin of seeded plants ~305 mya Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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 • Mosses are most closely related to vascular plants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryophyte • In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes • Sporophytes are typically present only part of the time mature sporophyte Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-8-3 1. spores develop into threadlike protonema protonema produces "buds" that grow into haploid gametes sperm swim through moisture to reach the egg meiosis occurs, spores develop in capsule. When mature lid opens sporophyte grows a long stalk (seta) which emerges from the archegonium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life Cycle of Moss • 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 (capsule), which discharges spores through a peristome which acts like teeth allowing it to open and close according to the environmental conditions • Hornwort and moss sporophytes have stomata for gas exchange Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9a Ph. Hepatophyta (Liverworth) Thallus Hepatophyta derives from Hepaticus= liver thalloid= flattened shape of gametophytes Gametophore of female gametophyte Sporophyte Foot absorbs nutrients Seta sends nutrients to the capsule gemma cup asexual reproduction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings produces spores by meiosis 500 µm Marchantia polymorpha, a “thalloid” liverwort Capsule (sporangium) Fig. 29-9c Ph. Anthocerophyta anthos= top; keras=horn sporophyta lacks seta, consists only of a sporangium horn splits open releasing spores (Hornworths) Sporophyte Gametophyte Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-9d Polytrichum commune, hairy-cap moss Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Gametophyte Ph. Bryophyta (Mosses) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bryo= mosses sperm requires water to reach egg male and female gametophytes The Ecological and Economic Importance of Mosses • Moses 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 Annual Nitrogen loss Kg/Ha 6 3 0 with moss Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings without moss • Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat • Sphagnum is an important global reservoir of organic carbon because of its acidic and oxygen-poor conditions (a) Peat being harvested (b) “Tollund Man,” a bog mummy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall • Bryophytes and bryophyte-like plants were the prevalent vegetation during the first 100 million years of plant evolution • Vascular plants began to diversify during the Devonian and Carboniferous periods • Vascular tissue allowed these plants to grow tall • Because seedless vascular plants have flagellated sperm they are usually restricted to moist environments Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Origins and Traits of Vascular Plants • Fossils of the forerunners of vascular plants date back about 420 million years • These early tiny plants had independent, branching sporophytes • Living vascular plants are characterized by: • Life cycles with dominant sporophytes • Vascular tissues called xylem and phloem • Well-developed roots and leaves Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-12 Aglaophyton major branching is typical of vascular plants www.adonline.id.au/plantevol/images sporophyte fossilized sample Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Life Cycles with Dominant Sporophytes • In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern • The gametophytes are tiny plants that grow on or below the soil surface Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-13-3 1. single spore develops into bysexual gametophyte prothallus Key Haploid (n) Diploid (2n) MEIOSIS Spore dispersal Spore (n) Sporangium Sporangium Antheridium Young gametophyte Mature gametophyte (n) Archegonium Egg Mature sporophyte (2n) New sporophyte Zygote (2n) FERTILIZATION Sorus sorus is a cluster of sporangia Gametophyte Fiddlehead zygotedevelops into a sporophyte Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sperm 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 • 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 • 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution of Leaves • 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 first, as outgrowths of stems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-14 Overtopping growth Vascular tissue Sporangia Microphyll Other stems become reduced and flattened. (a) Microphylls Megaphyll (b) Megaphylls Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Webbing develops. Sporophylls and Spore Variations • Sporophylls are modified leaves with sporangia • Sori are clusters of sporangia located on the underside of the sporophyll • Strobili are cone-like structures formed from groups of sporophylls strobilus sori Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-UN3 Seedless Homosporous spore production Sporangium on sporophyll Single type of spore Typically a bisexual gametophyte Eggs Sperm Seeded Heterosporous spore production Megasporangium on megasporophyll Megaspore Female gametophyte Eggs Microsporangium on microsporophyll Microspore Male gametophyte Sperm Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Classification of Seedless Vascular Plants • There are two phyla of seedless vascular plants: – Phylum Lycophyta includes club mosses, spike mosses, and quillworts – Phylum Pterophyta includes ferns, horsetails, and whisk ferns and their relatives Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-15a Lycophytes (Phylum Lycophyta) 2.5 cm Lyco=wolf small plants Isoetes Strobili (clusters of gunnii, a quillwort sporophylls) 1 cm Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-15e Pterophytes (Phylum Pterophyta) ptero= winged more than 12,000 species tropics, temperate and arid habitats share traits with seed plants (overtopping growth, megaphyll leaves and branching roots Psilotus, Equisetum 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 observe similarity with fossil Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-15f Fern Athyrium filix-femina Has megaphylls = fond Homosporous most of them fonds are made of leaflets 25 cm fond Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-15g Horsetail Equisetum arvense brushy appearance vegetative and cone bearing stems homosporous known as arthrophytes (joints in stems) small leaves stem is the main photosynthetic organ large air canals Vegetative stem 1.5 cm Strobilus on fertile stem Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-15h Whisk fern Psilotum nudum 2.5 cm dichotomus branching scalelike outgrowths that lack vascular tissue no roots, rhizoids instead "living fossils" 3 fused sporangia (yellow knob) homosporous bysexual gametophytes gametophytes grow underground gametophytes measure aprox. 1cm length Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 29-16 Concept of carboniferous era The End Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings