Transcript chapter23
The Plant Kingdom: Seedless Vascular Plants Chapter 23 Artist’s conception of a tropical Carboniferous forest. During the Carboniferous period, North America and Europe were considerably closer to the equator than they are today and had tropical swamp forests. Carboniferous forests in drier regions farther away from the equator were sparser and more open than the one depicted here. Lygodium overtaking cypress in Florida. LEARNING OBJECTIVE 1 • Summarize the features that distinguish seedless vascular plants from bryophytes KEY TERMS • XYLEM • • Vascular tissue that conducts water and dissolved minerals PHLOEM • Vascular tissue that conducts dissolved sugar and other organic compounds Seedless Vascular Plants • Adaptations that bryophytes lack • • • Vascular tissues (xylem and phloem) Dominant sporophyte generation As in bryophytes, reproduction depends on water to transport motile sperm cells Tasmanian Tree Fern Evolution of Seedless Vascular Plants SEEDLESS VASCULAR PLANTS B Seed plants Ferns Whisk ferns Horsetails FERNS Club mosses Spike mosses Quillworts LYCOPHYTES Evolution of seeds Evolution of microphylls Evolution of megaphylls A Ancestral vascular plant Fig. 23-2, p. 447 LEARNING OBJECTIVE 2 • Contrast microphylls and megaphylls KEY TERMS • • MICROPHYLL • Type of leaf found in lycophytes • Contains one vascular strand MEGAPHYLL • • Type of leaf found in virtually all vascular plants except lycophytes Contains multiple vascular strands True Leaves • Two basic types of true leaves, microphylls and megaphylls, evolved independently of each other Evolution of Leaves Stem Microphyll Vascular tissue Enation Vein Smooth stem Enation Vascular supply to enation (a) Microphyll evolution Microphyll (one vein) Thicker main Dichotomous Equal stem end branches branches Vascular tissue Thinner side branch Overtopping Dichotomously (unequal branching stems branching) (b) Megaphyll evolution Planation (branching in same plane) Webbing of side Megaphyll branch system (many veins) Fig. 23-3, p. 448 Stem Vascular tissue Microphyll Enation Vein Smooth Enation Vascular stem supply to (a) Microphyll evolution enation Thicker main Dichotomous stem end branches Equal branches Vascular tissue Microphyll (one vein) Thinner side branch Overtopping Dichotomously (unequal branching stems branching) (b) Megaphyll evolution Planation (branching in same plane) Webbing of side branch system Megaphyll (many veins) Stepped Art Fig. 23-3, p. 448 LEARNING OBJECTIVE 3 • Distinguish between the two phyla of seedless vascular plants KEY TERMS • FERNS (phylum Pteridophyta) • • • • Phylum of seedless vascular plants that reproduce by spores produced in sporangia Undergoes alternation of generations between dominant sporophyte and gametophyte (prothallus) Largest, most diverse group of seedless vascular plants Whisk ferns and horsetails classified as ferns KEY TERMS • LYCOPHYTES (phylum Lycopodiophyta) • • Phylum of seedless vascular plants, some of which are heterosporous Lycophytes include club mosses, spike mosses, quillworts Fern Diversity Fern Diversity Fern Diversity Fern Diversity LEARNING OBJECTIVE 4 • Name and briefly describe ferns • Explain why whisk ferns and horsetails are currently classified as ferns Fern Sporophytes 1 • Consist of • • • A rhizome that bears fronds (megaphylls) True roots Whisk fern sporophytes • • Have dichotomously branching rhizomes and erect stems Lack true roots and leaves Fern Sporophytes 2 • Horsetail sporophytes • • Roots, rhizomes, and aerial stems are hollow and jointed Leaves are reduced megaphylls Classification • Whisk ferns and horsetails were considered distinct enough to be classified in separate phyla • DNA comparisons and similarities in sperm structure resulted in reclassification as ferns Whisk Fern Sporangia Aerial stem with scale-like outgrowths (no leaves) Fig. 23-9a, p. 452 Whisk Fern Antheridia Archegonia Rhizoids (b) The gametophyte of P. nudum lives underground, nourished by mycorrhizae. Fig. 23-9b, p. 452 Ancient Horsetail Horsetails Strobilus Reproductive shoot Vegetative shoot (a) In some horsetail (Equisetum) species, both fertile shoots, which bear conelike strobili, and vegetative (nonreproductive) shoots are unbranched. Fig. 23-11a, p. 453 Horsetail Spores Spore Elater Fig. 23-12b, p. 456 LEARNING OBJECTIVE 5 • Describe the life cycle of ferns • Compare their sporophyte and gametophyte generations Life Cycle of Ferns 1 • Fern fronds bear sporangia in clusters (sori) • • Meiosis in sporangia produces haploid spores Fern gametophyte (prothallus) develops from a haploid spore • Bears both archegonia and antheridia Life Cycle of Ferns 2 • Each archegonium contains a single, nonmotile egg; each antheridium produces numerous sperm cells • Following fertilization, diploid zygote grows by mitosis into a multicellular embryo (immature sporophyte) Animation: Fern Life Cycle CLICK TO PLAY Fern Life Cycle Underside of enlarged mature gametophyte (prothallus) Germination of spores and development of young gametophyte Egg 5 4 Spores released Rhizoids 3 Antheridium Sporangium Meiosis Sorus 2 (cluster of sporangia) Archegonium HAPLOID (n) GAMETOPHYTE GENERATION Cells within sporangia undergo meiosis Sperm cell Fertilization DIPLOID (2n) SPOROPHYTE GENERATION Frond Zygote 6 1 Leaf of young sporophyte Leaf cross section Haploid prothallus Fiddlehead Roots Underside of a frond Fern (mature sporophyte) Development of the sporophyte Rhizome Root of young sporophyte Fig. 23-5, p. 450 Fiddleheads Sori Prothallus Archegonium Rhizoids Fig. 23-8, p. 451 LEARNING OBJECTIVE 6 • Name and briefly describe the three groups of lycophytes 3 Groups of Lycophytes 1. Club moss sporophyte • • • true roots rhizomes and erect or trailing aerial stems small, scalelike microphylls Club Mosses Strobilus Leaves (microphylls) (a) The sporophyte of Lycopodium obscurum has small, scalelike, evergreen leaves (microphylls). Spores are produced in sporangia on fertile leaves clustered in a conelike strobilus. (b) Vegetative growth of Lycopodium complanatum, which has a creeping growth form. Like most club mosses, L. complanatum prefers moist, shady woodlands. Fig. 23-14, p. 457 3 Groups of Lycophytes 2. Spike moss sporophyte • • • long, creeping rhizomes that typically branch dichotomously roots that branch dichotomously overlapping, scalelike microphylls Spike Moss Resurrection Plant 3 Groups of Lycophytes 3. Quillwort sporophyte • • • underground corm cylindrical, quill-like microphylls roots Quillworts LEARNING OBJECTIVE 7 • Compare the generalized life cycle of a homosporous plant with that of a heterosporous plant KEY TERMS • HOMOSPORY • • Production of one type of n spore that gives rise to a bisexual gametophyte HETEROSPORY • Production of two types of n spores, microspores and megaspores KEY TERMS • MICROSPORE • • The n spore in heterosporous plants that gives rise to a male gametophyte that produces sperm cells within antheridia MEGASPORE • The n spore in heterosporous plants that gives rise to a female gametophyte that produces eggs within archegonia Life Cycle: Heterosporous Plants Gametophyte Megaspore Microspore Meiosis Antheridium HAPLOID (n) GAMETOPHYTE GENERATION DIPLOID (2n) SPOROPHYTE GENERATION Microspore mother cell Megaspore mother cell Archegonium Gametophyte Sperm Egg Fertilization Zygote Microsporangium Embryo Megasporangium Sporophyte Fig. 23-17, p. 459 Life Cycle: Selaginella Male gametophyte develops inside microspore wall 3 Single antheridium in male gametophyte produces many sperm cells 2 Microspores 5 Sperm cell Ruptured Archegonium megaspore wall containing egg Female gametophyte develops and protrudes 4 from megaspore wall Longitudinal section through Megaspores archegonium Egg HAPLOID (n) GAMETOPHYTE GENERATION Meiosis Fertilization Microsporangium DIPLOID (2n) with microspore SPOROPHYTE mother cells GENERATION Female Megasporangium with megaspore Strobilus gametophyte mother cells First 1 leaves Leaf (microphyll) Stem Zygote Stem Longitudinal section 6 Root through strobilus Root Young sporophyte Mature (attached to female sporophyte gametophyte) Fig. 23-18, p. 460 LEARNING OBJECTIVE 8 • Name and describe one of Earth’s earliest vascular plants Oldest Vascular Plants • Phylum Rhyniophyta • According to fossil record, arose about 420 mya and became extinct about 380 mya Early Vascular Plant • Rhynia gwynne-vaughanii • • • • • Superficially resembled whisk ferns Leafless upright stems branched dichotomously from an underground rhizome Lacked roots, but had absorptive rhizoids Sporangia formed at ends of short branches Internal structure of rhizome contained a central core of xylem cells for conducting water and minerals Rhynia gwynne-vaughanii Aglaophyton major LEARNING OBJECTIVE 9 • Describe the ecological and economic significance of the ferns and lycophytes Ecology and Economics 1 • Ferns and lycophytes help form soil, prevent erosion • • Branching underground rhizomes and roots or rhizoids hold soil in place Living species of limited economic importance • Many cultivated for aesthetic appeal Ecology and Economics 2 • Coal deposits • • Formed from remains of ancient ferns, club mosses, horsetails Powered Industrial Revolution of 19th century, used today to produce electricity