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Transcript
The Land Plants Chapter 23 Part 1 Impacts, Issues Beginnings and Endings Land plants provide oxygen, food, and shelter to humans and animals, but human activities are pushing some species toward extinction 23.1 Evolution on a Changing World Stage Changes in atmospheric conditions and shifts in positions of continents affected the evolutionary history of land plants Evolution of Land Plants Land plants (embryophytes) evolved from a lineage of green algae (charophytes) after the ozone layer made life on land possible red algae chlorophytes charophytes land plants p. 370 Evolution of Land Plants Bryophytes include three early diverging land plant lineages Nonvascular seedless plants evolved next The first seed plants were gymnosperms, from which angiosperms (flowering plants) evolved Evolutionary Tree for Land Plants Fig. 23-2a, p. 370 bryophytes seedless vascular plants gymnosperms angiosperms (flowering plants) Seed Plants Vascular Plants Land Plants ancestral green alga Fig. 23-2a, p. 370 bryophyte (moss) Fig. 23-2b (1), p. 370 seedless vascular plant (fern) Fig. 23-2b (2), p. 370 gymnosperm (conifer) Fig. 23-2b (3), p. 370 angiosperm (monocot) Fig. 23-2b (4), p. 370 Diversity of Modern Land Plants Timeline for Plant Evolution Continental movements that caused global climate to become drier favored groups that were better adapted to drought (seed plants) • • • • • Silurian: Small seedless vascular plants Carboniferous: Large seedless vascular plants Devonian: First seeds (gymnosperms) Permian-Jurassic: Drought-tolerant conifers Jurassic-Cretaceous: Flowering plants Timeline for Plant Evolution Gondwana 425 Origin of first land plants (bryophytes) by 475 mya. Origin of seedless vascular plants. Ordovician Silurian 488 443 425 mya Bryophytes and seedless vascular plants diversify. Seed plants arise by 385 mya. Devonian 416 342 mya Tree-sized lycophytes and horsetails live in swamp forests. First conifers arise late in Carboniferous. Carboniferous 359 Pangea 255 mya Ginkgos, cycads appear. Most horsetails and lycophytes disappear by the end of the Permian. Permian 299 Adaptive radiations of ferns, cycads, conifers; by start of Cretaceous, conifers are dominant trees. 65 mya Flowering plants appear in the early Cretaceous, undergo adaptive radiation and become dominant. Triassic Jurassic Cretaceous Tertiary 251 200 146 66 Millions of years ago (mya) Fig. 23-3, p. 371 Early Seedless Vascular Plants Cooksonia and Psilophyton 23.2 Evolutionary Trends Among Plants Over time, the spore-producing bodies of plants became larger, more complex, and better adapted to dry habitats From Haploid to Diploid Dominance Plants shifted from gametophyte-dominated life cycle (in bryophytes) to sporophyte-dominated life cycle (in other plants) • Gametophyte: Haploid stage that forms gametes by mitosis • Sporophyte: Diploid stage that forms spores by meiosis; a sporangium helps protect and disperse spores Life Cycle of Land Plants Fig. 23-5a, p. 372 mitosis multicelled sporophyte (2n) zygote (2n) fertilization DIPLOID meiosis HAPLOID gametes (n) mitosis multicelled gametophyte (n) spores (n) mitosis Fig. 23-5a, p. 372 Fig. 23-5b, p. 372 zygote is only diploid phase green algae bryophytes ferns gymnosperms angiosperms Fig. 23-5b, p. 372 Animation: Haploid to diploid dominance Roots, Stems, and Leaves Life on land favored water conserving features • Cuticle: Waxy layer that restricts evaporation • Stomata: Openings across the cuticle cuticle (waxy layer at leaf surface) Fig. 23-6a, p. 373 stoma (opening across cuticle) Fig. 23-6b, p. 373 Roots, Stems, and Leaves In vascular plants, a system of vascular tissue reinforced by lignin distributes materials through leaves, stems, and roots of sporophytes • Xylem: Distributes water and minerals • Phloem: Distributes products of photosynthesis Vascular Tissues xylem Fig. 23-7a, p. 373 xylem phloem Fig. 23-7b, p. 373 Pollen and Seeds Bryophytes and seedless plants release spores Only seed-bearing vascular plants release pollen grains and seeds • Pollen grain: A walled, immature gametophyte that will give rise to the sperm • Seed: An embryo sporophyte and some nutritive tissue enclosed inside a waterproof coat Two Lineages of Seed-Bearing Vascular Plants Gymnosperms • Cycads, conifers, ginkgos, and gnetophytes Angiosperms (flowering plants) • Most modern plants • Seeds form inside floral tissue that later develops into a fruit Dispersal Methods: Spores and Seeds 23.1-23.2 Key Concepts Milestones in Plant Evolution The earliest known plants date from 475 million years ago Ever since then, environmental changes have triggered divergences, adaptive radiations, and extinctions Structural and functional adaptations of lineages are responses to some of the changes 23.3 The Bryophytes Bryophytes include three land plant lineages – liverworts, hornworts, and mosses – with a gametophyte-dominated life-cycle Characteristics of Bryophytes Nonvascular (no xylem or phloem) Sperm swim through water to eggs The sporophyte forms on, and is nourished by, the dominant gametophyte Spores are the dispersal form Liverworts Gametophyte has a thallus that attaches to soil or surfaces by rootlike rhizoids Reproduces sexually, or asexually by producing gemmae in cups on the gametophyte Liverwort: Marchantia thallus (leaflike part) with gemmae cups Fig. 23-9a, p. 374 asexually-produced gemmae in cup Fig. 23-9b, p. 374 sperm-producing structure of a male plant Fig. 23-9c, p. 374 egg-producing structure of a female plant Fig. 23-9d, p. 374 Hornworts Have a hornlike sporophyte with its base embedded in gametophyte tissue; spores form in an upright capsule (sporangium) • Sporophyte has chloroplasts • Gametophyte has nitrogen-fixing bacteria sporophyte gametophyte p. 374 Mosses Sporophyte consists of a capsule (sporangium) embedded in gametophyte Life cycle • Haploid spores form in the capsule by meiosis, germinate, and develop into gametophytes • Eggs and sperm form in gametangia • After fertilization, zygote develops into sporophyte Moss Life Cycle: Polytrichum G Zygote grows, develops into a sporophyte while still attached to gametophyte. A Mature moss sporophyte consists of a capsule atop a stalk. It is still attached to the gametophyte. sporophyte zygote Diploid Stage Haploid Stage gametophyte fertilization F Drops of rain disperse sperm, which swim to eggs and fertilize them. spermproducing antheridium D Sperm form at tips of male gametophyte. eggproducing archegonium E Eggs form at tip of female gametophyte. rhizoids meiosis B Meiosis of cells inside the capsule forms spores, which are released when the capsule pops open. male female immature gametophytes C Spores germinate, grow, and develop into gametophytes. Fig. 23-10, p. 375 G Zygote grows, develops into a sporophyte while still attached to gametophyte. A Mature moss sporophyte consists of a capsule atop a stalk. It is still attached to the gametophyte. sporophyte zygote Diploid Stage gametophyte Haploid Stage fertilization F Drops of rain disperse sperm, which spermswim to producing eggs and fertilize them. antheridium rhizoids D Sperm form at tips of male gametophyte. meiosis B Meiosis of cells inside the capsule forms spores, which are released when the capsule pops open. male eggproducing archegonium E Eggs form at tip of female gametophyte. female immature gametophytes C Spores germinate, grow, and develop into gametophytes. Stepped Art Fig. 23-10, p. 375 Animation: Moss life cycle Importance of Mosses Mosses are the most diverse group of bryophytes; peat mosses (Sphagnum) are ecologically and commercially important Fig. 23-11a, p. 375 sporophyte gametophyte Fig. 23-11b, p. 375 23.3 Key Concepts Early-Diverging Plant Lineages Three plant lineages (mosses, hornworts, and liverworts) are commonly referred to as bryophytes, although they are not a natural group The gamete-producing stage dominates their life cycle, and sperm reach the eggs by swimming through droplets or films of water 23.4 Seedless Vascular Plants A sporophyte with lignified vascular tissue (xylem and phloem) dominates the life cycle Two lineages of seedless vascular plants • Lycophytes (club mosses, spike mosses) • Monilophytes (whisk ferns, horsetails, ferns) Some Lycophytes Club moss (Lycopodium) • Spores form inside a soft, cone-shaped strobilus Spike moss (Selaginella) “resurrection plant” • The most drought-tolerant vascular plants Whisk Ferns Whisk ferns (Psilotum) • Have rhizomes (underground stems) but no roots • Photosynthetic stems appear leafless • Spores form in fused sporangia at tips of branches Horsetails Horsetails (Equisetum) • Have rhizomes, hollow stems with silica deposits, and nonphotosynthetic leaves • Photosynthesis occurs in stems and leaflike branches • Spores in strobili form tiny gametophytes Seedless Vascular Plants Club moss (Lycopodium), whisk fern (Psilotum), and horsetails (Equisetum) strobilus Fig. 23-12a, p. 376 sporangia Fig. 23-12b, p. 376 leaflike branch Fig. 23-12c, p. 376 strobilus Fig. 23-12d, p. 376 Ferns – No Seeds, Much Diversity Ferns • The most diverse seedless vascular plants • Most sporophytes have leaves and roots that grow out from rhizomes • Spores are dispersed from clusters of sporangia (sori) on lower surfaces of frond leaves • Many live as epiphytes attached to another plant Fern Life Cycle: Woodwardia The sporophyte (still attached to the gametophyte) grows, develops. zygote rhizome Diploid Stage fertilization egg sperm meiosis Haploid Stage eggproducing archegonium spermproducing antheridium sorus Spores develop. mature gametophyte (underside) Spores are released. C A spore germinates, grows into a gametophyte. Stepped Art Fig. 23-13, p. 377 The sporophyte (still attached to the gametophyte) grows, develops. zygote rhizome sorus Diploid Stage fertilization egg sperm Haploid Stage eggproducing archegonium spermproducing antheridium meiosis Spores develop. mature gametophyte (underside) Spores are released. A spore germinates, grows into a gametophyte. Fig. 23-13, p. 377 Animation: Fern life cycle Fern Diversity Fig. 23-14a, p. 377 Fig. 23-14b, p. 377 Fig. 23-14c, p. 377 Animation: Alternations of generations Animation: Evolutionary tree for plants Animation: Marchantia, a liverwort Animation: Milestones in plant evolution Animation: Seedless vascular plants