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Chapter 29 Plant Diversity I How Plants Colonized Land PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An Overview of Land Plant Evolution • 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 • Land plants evolved from green algae (chlorophyta): – Researchers have identified green algae called charophyceans as the closest relatives of land plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Plants • The first plants evolved from an organism much like the multicellular green algae living today – However, the evolution of plants favored species that were more resistant to the drying rays of the sun! Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of Land Plant Evolution • > 280,000 species of plants inhibit Earth today. • 4 major evolutionary trends characterize plants today: – Movement to land (new niches) – Development of vascular tissue (taller growth) – Development of seeds (dispersal of offspring) – Development of flowers (pollinators) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 29.1 Some highlights of plant evolution Morphological and Biochemical Evidence • Land plants evolved from charophycean algae over 500 million years ago. There are four key traits that land plants share only with charophyceans: – Rose-shaped complexes for cellulose synthesis • – Peroxisome enzymes • – Help minimize the loss of organic product due to photorespiration Structure of flagellated sperm • – Rose-shaped array of proteins that synthesize the cellulose microfibrils of the cell wall Used for sperm motility Formation of a phragmoplast • An alignment of cytoskeletal elements and Golgi-derived vesicles across the midline of the dividing cell. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Derived Traits of Plants • Five key traits appear in nearly all land plants but are absent in the charophyceans: – Apical meristems – Multicellular dependent embryos – Alternation of generations – Walled spores produced in sporangia – Multicellular gametangia Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Apical Meristems – Producers of Plant’s Tissues • These are localized regions of cell division at the tips of shoots and roots. – Maximize their exposure to environmental resources. Developing leaves Apical meristem of shoot Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Apical meristem of root Multicellular Dependent Embryos • Multicellular plant embryos develop from zygotes that are retained within tissues of the female parent. – Parental tissues provide developing embryo with nutrients. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alternation of Generations Life Cycle • During the life cycle of ALL land plants, two multicellular body forms alternate, each form producing the other. – Called alternation of generations – Cells of gametophyte generation are haploid (single set of chromosomes) – produces gametes • Fusion of gametes (eggs and sperm) during fertilization forms diploid zygotes. – Mitotic division of the zygote produces the multicellular sporophyte (diploid). • Meiosis in a mature sporophyte produces haploid reproductive cells called spores (reproductive cells that can develop into a new organism without fusing with another cell). Mitotic division of spore produces new gametophyte…so cycle continues. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 29.6 Alternation of generations: a generalized scheme Walled Spores Produced in Sporangia • Plant spores are haploid reproductive cells that have the potential to grow into multicellular, haploid gametophytes by mitosis. – A polymer called sporopollenin (durable organic material) makes walls of plant spores tough and resistant to harsh environments. – Multicellular organs called sporangia, found on the sporophyte generation of a plant, produce the spores. – The outer tissues of the sporangium protect developing spores until they are ready to be released – a key adaptation in land plants. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Multicellular Gametangia • The gametophyte forms of bryophytes, pteridophytes, and gymnosperms all produce their gametes within multicellular organs called gametangia. – Female gametangia are called archegonia – Male gametangia are called antheridia Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other Terrestrial Adaptations Common to Land Plants • Adaptations for water conservation – Cuticle (waxy cover on surface of stems and leaves) – Stomata (pore on leaves allowing for gas exchange) • Adaptations for Water Transport – Xylem (carries water and minerals from roots to rest of plant) – Phloem (carries sugars and other nutrients throughout plant) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 Main Groups of Land Plants • Bryophytes: non-vascular plants – mosses, hornworts, and liverworts • Pteridophytes: seedless vascular plants – Club moss, horsetails, ferns • Gymnosperms: vascular seeded cone-bearers – Ginkgos, cycads, gnetophytes, conifers • Angiosperms: vascular seeded flowering plants – Monocots & dicots Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 22-7 The Diversity of Plants 22-1 LandSection plants can be informally grouped based on the presence or absence of vascular tissue Cone-bearing plants 760 species Ferns and their relatives 11,000 species Mosses and their relatives 15,600 species Go to Section: Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Flowering plants 235,000 species Table 29.1 Ten Phyla of Extant Plants An Overview of Land Plant Evolution Land plants Vascular plants Figure 29.7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Angiosperms Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Seed plants Gymnosperms Pterophyte (ferns, horsetails, whisk fern) Seedless vascular plants Lycophytes (club mosses, spike mosses, quillworts) Mosses Hornworts Liverworts Charophyceans Bryophytes (nonvascular plants) Bryophytes – Nonvascular Plants • The life cycles of mosses and other bryophytes are dominated by the gametophyte stage • Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants – Liverworts, phylum Hepatophyta – Hornworts, phylum Anthocerophyta – Mosses, phylum Bryophyta • In all three bryophyte phyla – Gametophytes are larger and longer-living than sporophytes – Water is required for survival AND reproduction – absorb water by diffusion – Have no true roots, stems, and leaves and lack lignin-fortified tissue required to support tall plants on land Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life Cycle of Moss Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bryophyte Diversity Gametophore of female gametophyte LIVERWORTS (PHYLUM HEPATOPHYTA) Plagiochila deltoidea, a “leafy” liverwort Foot Seta Marchantia sporophyte (LM) HORNWORTS (PHYLUM ANTHOCEROPHYTA) An Anthoceros hornwort species Sporophyte Sporangium 500 µm Marchantia polymorpha, a “thalloid” liverwort MOSSES (PHYLUM BRYOPHYTA) Polytrichum commune, hairy-cap moss Sporophyte Gametophyte Gametophyte Figure 29.9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tracheophytes – Vascular Plants • Most common and widespread of land plants • Have true vascular tissues -- xylem and phloem that allow true “organs” to develop – roots, stems, leaves – Xylem carries water and minerals in a plant – Phloem carries nutrients in a plant • Two categories – Seedless (reproduce by spores) – Seeded (reproduce by seeds) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life Cycles with Dominant Sporophytes • In contrast with bryophytes – The 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 © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Life Cycle of a Fern 1 Sporangia release spores. Most fern species produce a single type of spore that gives rise to a bisexual gametophyte. Key 2 The fern spore develops into a small, photosynthetic gametophyte. 3 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanisms promote cross-fertilization between gametophytes. Haploid (n) Diploid (2n) Antheridium Spore MEIOSIS Young gametophyte Sporangium Archegonium Mature sporophyte New sporophyte Sperm Egg Zygote Sporangium FERTILIZATION Sorus 6 On the underside of the sporophyte‘s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia. Gametophyte Fiddlehead Figure 29.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 A zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. 4 Fern sperm use flagella to swim from the antheridia to eggs in the archegonia. Transport in Xylem and Phloem • Vascular plants have two types of vascular tissue: xylem and phloem • Xylem – Conducts most of the water and minerals – Includes dead cells called tracheids • Phloem – Distributes sugars, amino acids, and other organic products – Consists of living cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Roots • Roots are organs that anchor vascular plants – Enable vascular plants to absorb water and nutrients from the soil – May have evolved from subterranean stems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Leaves • Leaves – Are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis • Leaves are categorized by two types – Microphylls, leaves with a single vein – Megaphylls, leaves with a highly branched vascular system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sporophylls and Spore Variations • Sporophylls are modified leaves with sporangia • 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, having two types of spores that give rise to male and female gametophytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Life Cycle of a Fern 1 Sporangia release spores. Most fern species produce a single type of spore that gives rise to a bisexual gametophyte. Key 2 The fern spore develops into a small, photosynthetic gametophyte. 3 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanisms promote cross-fertilization between gametophytes. Haploid (n) Diploid (2n) Antheridium Spore MEIOSIS Young gametophyte Sporangium Archegonium Mature sporophyte New sporophyte Sperm Egg Zygote Sporangium FERTILIZATION Sorus 6 On the underside of the sporophyte‘s reproductive leaves are spots called sori. Each sorus is a cluster of sporangia. Gametophyte Fiddlehead Figure 29.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 A zygote develops into a new sporophyte, and the young plant grows out from an archegonium of its parent, the gametophyte. 4 Fern sperm use flagella to swim from the antheridia to eggs in the archegonia. Figure 29.24b Fern sporophyll, a leaf specialized for spore production Classification of Seedless Vascular Plants • Seedless vascular plants form two phyla – Lycophyta, including club mosses, spike mosses, and quillworts – Pterophyta, including ferns, horsetails, and whisk ferns and their relatives • Since they don’t have seeds, they need LOTS of water for fertilization – USE SPORES TO REPRODUCE FOR MAJORITY OF LIFE; gametes are used only for a short period of time • Display alternation of generations – part of time is asexual (uses spores), part is sexual (uses gametes) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings General Groups of Seedless Vascular Plants LYCOPHYTES (PHYLUM LYCOPHYTA) Strobili (clusters of sporophylls) Isoetes gunnii, a quillwort Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss PTEROPHYTES (PHYLUM PTEROPHYTA) Psilotum nudum, a whisk fern Equisetum arvense, field horsetail Athyrium filix-femina, lady fern Vegetative stem Strobilus on fertile stem Figure 29.14 WHISK FERNS AND RELATIVES HORSETAILS Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings FERNS Figure 29.21 Pteridophytes: club "moss" (top left), whisk fern (top right), horsetail (bottom left), fern (bottom right) Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts • Modern species of lycophytes – Are relics from a far more eminent past – Are small herbaceous plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives • Ferns – Are the most diverse seedless vascular plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Significance of Seedless Vascular Plants • The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Carboniferous, forming the first forests Figure 29.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Significance of Seedless Vascular Plants • The growth of these early forests – May have helped produce the major global cooling that characterized the end of the Carboniferous period – Decayed and eventually became coal Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evolution of Plants Vascular w/ Seeds Vascular w/ Seeds Angiosperms Vascular Seedless Gymnosperms Non-Vascular Pterophyta Flowering plants Bryophytes Cone-bearing plants Ferns and their relatives Flowers; Seeds Enclosed in Fruit Mosses and their relatives Seeds Water-Conducting (Vascular) Tissue Green algae ancestor