29 Lectures PPT

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Published on February 12, 2008

Author: Urania

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Chapter 29:  Chapter 29 Plant Diversity I How Plants Colonized Land Overview: The Greening of Earth:  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 Concept 29.1: Land plants evolved from green algae:  Concept 29.1: Land plants evolved from green algae Green algae called charophyceans are the closest relatives of land plants Morphological and Biochemical Evidence:  Morphological and Biochemical 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 charophyceans: Rose-shaped complexes for cellulose synthesis Peroxisome enzymes Structure of flagellated sperm Formation of a phragmoplast Genetic Evidence:  Genetic Evidence Comparisons of both nuclear and chloroplast genes point to charophyceans as the closest living relatives of land plants LE 29-3:  LE 29-3 10 mm 40 µm Chara, a pond organism (LM). Coleochaete orbicularis, a disk-shaped charophycean (LM). Adaptations Enabling the Move to Land:  Adaptations Enabling the Move to Land In charophyceans a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants Concept 29.2: Land plants possess a set of derived terrestrial adaptations:  Concept 29.2: Land plants possess a set of derived terrestrial adaptations Many adaptations emerged after land plants diverged from their charophycean relatives Defining the Plant Kingdom:  Defining the Plant Kingdom Systematists are currently debating the boundaries of the plant kingdom 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 LE 29-4:  LE 29-4 Viridiplantae Streptophyta Plantae Red algae Chlorophytes Charophyceans Embryophytes Ancestral alga Derived Traits of Plants:  Derived Traits of Plants Five key traits appear in nearly all land plants but are absent in the charophyceans: Apical meristems Alternation of generations Walled spores produced in sporangia Multicellular gametangia Multicellular dependent embryos LE 29-5a:  LE 29-5a Apical Meristem of shoot Developing leaves Shoot Root Apical meristem 100 µm 100 µm Apical Meristems LE 29-5b:  LE 29-5b Mitosis Alternation of Generations Spores Mitosis Mitosis Zygote Gametes Haploid multicellular organism (gametophyte) Diploid multicellular organism (sporophyte) MEIOSIS FERTILIZATION LE 29-5c:  LE 29-5c Walled Spores Produced in Sporangia Multicellular Gametangia Multicellular, Dependent Embryos Longitudinal section of Sphagnum sporangium (LM) Spores Sporangium Sporophyte Gametophyte Sporophyte and sporangium of Sphagnum (a moss) Archegonia and antheridia of Marchantia (a liverwort) Male gametophyte Antheridium with sperm Female gametophyte Archegonium with egg Maternal tissue Embryo 2 µm 10 µm Wall ingrowths Placental transfer cell Slide17:  Additional derived traits such as a cuticle and secondary compounds evolved in many plant species The Origin and Diversification of Plants:  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 LE 29-6:  LE 29-6 Fossilized spores. Unlike the spores of most living plants, which are single grains, these spores found in Oman are in groups of four (left; one hidden) and two (right). Fossilized sporophyte tissue. The spores were embedded in tissue that appears to be from plants. Slide20:  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 LE 29-7:  LE 29-7 Ancestral green alga Origin of land plants (about 475 mya) Origin of vascular plants (about 420 mya) Origin of seed plants (about 360 mya) Land plants Vascular plants Seed plants Seedless vascular plants Bryophytes Liverworts Hornworts Mosses Lycophytes Pterophytes Gymno- sperms Angio- sperms Charophyceans Concept 29.3: The life cycles of mosses and other bryophytes are dominated by the gametophyte stage:  Concept 29.3: 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 Slide24:  Debate continues over the sequence of bryophyte evolution Mosses are most closely related to vascular plants Bryophyte Gametophytes:  Bryophyte Gametophytes In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time Animation: Moss Life Cycle LE 29-8:  LE 29-8 Male gametophyte “Bud” Spores develop into threadlike protonemata. Protonemata “Bud” The haploid protonemata produce “buds” that grow into gametophytes. Raindrop Sperm Antheridia Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. Egg Haploid (n) Diploid (2n) Key A sperm swims through a film of moisture to an archegonium and fertilizes the egg. Archegonia Rhizoid Female gametophyte Gametophore Spores Sporangium Peristome MEIOSIS Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores. The sporophyte grows a long stalk, or seta, that emerges from the archegonium. FERTILIZATION (within archegonium) Archegonium Zygote Embryo Calyptra Young sporophyte Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. The diploid zygote develops into a sporophyte embryo within the archegonium. Capsule (sporangium) Seta Foot Mature sporophytes Capsule with peristome (SEM) Female gametophytes Slide27:  Bryophyte gametophytes Produce flagellated sperm in antheridia Produce ova in archegonia Generally form ground-hugging carpets and are at most only a few cells thick Some mosses have conducting tissues in the center of their “stems” and may grow vertically Bryophyte Sporophytes:  Bryophyte Sporophytes Bryophyte sporophytes Grow out of archegonia Are the smallest and simplest of all extant plant groups Consist of a foot, a seta, and a sporangium Hornwort and moss sporophytes have stomata LE 29-9a:  LE 29-9a Gametophore of female gametophyte Marchantia polymorpha, a “thalloid” liverwort Foot Seta Sporangium 500 µm Marchantia sporophyte (LM) LE 29-9b:  LE 29-9b Plagiochila deltoidea, a “leafy” liverwort LE 29-9c:  LE 29-9c An Anthroceros hornwort species Sporophyte Gametophyte LE 29-9d:  LE 29-9d Polytrichum commune, hairy cap moss Sporophyte Gametophyte Ecological and Economic Importance of Mosses:  Ecological and Economic Importance of Mosses Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Sphagnum plays an important role in the Earth’s carbon cycle LE 29-10:  LE 29-10 A peat bog. Gametophyte Sporangium at tip of sporophyte Living photo- synthetic cells Dead water- storing cells 100 µm Closeup of Sphagnum. Note the “leafy” Gametophytes and their offspring, the sporophytes. Sphagnum “leaf” (LM). The combination of living photosynthetic cells and dead water-storing cells gives the moss its spongy quality. “Tolland Man,” a bog mummy dating from 405–100 B.C. The acidic, oxygen-poor conditions produced by Sphagnum can preserve human or animal bodies for thousands of years. Concept 29.4: Ferns and other seedless vascular plants formed the first forests:  Concept 29.4: Ferns and other seedless vascular plants formed the first forests 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 Carboniferous period Vascular plants dominate most landscapes today Origins and Traits of Vascular Plants:  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 They lacked other derived traits of vascular plants Life Cycles with Dominant Sporophytes:  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 Animation: Fern Life Cycle LE 29-12:  LE 29-12 Spore Sperm Antheridium Egg Haploid (n) Diploid (2n) Key Young gametophyte Sorus Sporangium MEIOSIS FERTILIZATION Archegonium Zygote New sporophyte Mature sporophyte Sporangium Gametophyte Fiddlehead Transport in Xylem and Phloem:  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 Evolution of Roots:  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 Evolution of Leaves:  Evolution of Leaves Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis Slide43:  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 LE 29-13:  LE 29-13 Vascular tissue Microphylls Megaphylls Sporophylls and Spore Variations:  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 Classification of Seedless Vascular Plants:  Classification of Seedless Vascular Plants There are two phyla of seedless vascular plants: Lycophyta includes club mosses, spike mosses, and quillworts Pterophyta includes ferns, horsetails, and whisk ferns and their relatives LE 29-14a:  LE 29-14a Selaginella apoda, a spike moss LE 29-14b:  LE 29-14b Isoetes gunnii, a quillwort LE 29-14c:  LE 29-14c Diphasiastrum tristachyum, a club moss Strobili (clusters of sporophyllis) LE 29-14d:  LE 29-14d Psilotum nudum, a whisk fern LE 29-14e:  LE 29-14e Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem LE 29-14f:  LE 29-14f Athyrium filix-femina, lady fern Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts:  Phylum Lycophyta: Club Mosses, Spike Mosses, and Quillworts Giant lycophytes thrived for millions of years in moist swamps Surviving species are small herbaceous plants Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives:  Phylum Pterophyta: Ferns, Horsetails, and Whisk Ferns and Relatives Ferns are the most diverse seedless vascular plants, with more than 12,000 species They are most diverse in the tropics but also thrive in temperate forests Some species are even adapted to arid climates The Significance of Seedless Vascular Plants:  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 These forests may have helped produce the global cooling at the end of the Carboniferous period The decaying plants of these Carboniferous forests eventually became coal

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