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Biology Sylvia S. Mader Michael Windelspecht Chapter 24 Flowering Plants: Structure and Organization Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outline • 24.1 Organs of Flowering Plants • 24.2 Tissues of Flowering Plants • 24.3 Organization and Diversity of Roots • 24.4 Organization and Diversity of Stems • 24.5 Organization and Diversity of Leaves 2 24.1 Organs of Flowering Plants • Flowering plants, or angiosperms, are extremely diverse but share many common structural features. • Most flowering plants possess a root system and a shoot system The root system simply consists of the roots, The shoot system consists of the stem and leaves. • A typical plant features three vegetative organs roots, stems, and leaves Vegetative organs are concerned with growth and nutrition. • Flowers, seeds, and fruits are structures involved in 3 reproduction. Organization of Plant Body Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. terminal bud blade leaf vein petiole axillary bud stem node internode node vascular tissues shoot system root system branch root root hairs primary root 4 Organs of Flowering Plants • Roots Generally, the root system is at least equivalent in size and extent to the shoot system • Anchors plant in soil • Absorbs water and minerals from the soil • Produces hormones Root hairs: • Projections from epidermal root-hair cells • Greatly increase absorptive capacity of root 5 Organs of Flowering Plants • Stems Shoot system of a plant is composed of the stem, branches, and leaves • Stem is the main axis of a plant that elongates and produces leaves – Nodes occur where leaves are attached to the stem – Internode is region between nodes – Axillary buds can produce new branches of the stem (or flowers) • Stem also has vascular tissue that transports water and minerals 6 Organs of Flowering Plants • Leaves major part of the plant that carries on photosynthesis • Foliage leaves are usually broad and thin – Blade - Wide portion of foliage leaf – Petiole - Stalk attaching blade to stem – Leaf Axil - Upper acute angle between petiole and stem where the axillary bud is found • Tendrils - Leaves that attach to objects • Bulbs - Leaves that store food 7 Vegetative Organs of Several Eudicots Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. blade petiole stems stem roots lateral root a. Root system, dandelion b. Shoot system, bean seedling c. Leaves, pumpkin seedling a: © Dorling Kindersley/Getty Images; b:© Dwight Kuhn; c: © Dwight Kuhn 8 Organs of Flowering Plants • Monocots (Single cotyledon) Cotyledons act as transfer tissue • Nutrients are derived from the endosperm Root vascular tissue occurs in ring Parallel leaf venation Flower parts arranged in multiples of three • Eudicots (Two cotyledons) Cotyledons supply nutrients to seedlings Root phloem located between xylem arms Netted leaf venation Flower parts arranged in multiples of four or five 9 Flowering Plants are Either Monocots or Eudicots Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Root Stem Leaf Vascular bundles scattered in stem Leaf veins form a parallel pattern Flower Monocots Seed Root xylem and phloem in a ring Flower parts in threes and multiples of three Eudicots One cotyledon in seed Two cotyledons in seed Root phloem between arms of xylem Vascular bundles in a distinct ring Leaf veins form a net pattern Flower parts in fours or fives and their multiples 10 24.2 Tissues of Flowering Plants • Meristematic tissue enables flowering plants to grow throughout their lifetime • Apical meristems at the tips of stems and roots increase the length of these tissues • Apical meristem produces three types of meristem, which produce three specialized tissues Epidermal tissue Ground tissue Vascular tissue 11 Tissues of Flowering Plants • Epidermal Tissue Forms the outer protective covering of a plant Epidermis contains closely packed epidermal cells • Epidermal cells exposed to air are covered with waxy cuticle • Root epidermal cells have root hairs • Epidermal cells of stems, leaves, and reproductive organs have trichomes • Lower leaf surface contains stomata In older woody plants, the epidermis of the stem is replaced by periderm • Major component is cork • New cork is made by cork cambium 12 Modifications of Epidermal Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. corn seedling guard cell chloroplasts periderm lenticel cork cambium cork root hairs enlongating root tip a. Root hairs Stoma b. Stoma of leaf nucleus c. Cork of older stem a: © Evelyn Jo Johnson; b: © J.R. Waaland/Biological Photo Service; c: © Kingsley Stern 13 Tissues of Flowering Plants • Ground tissue forms bulk of a flowering plant Parenchyma cells: • Least specialized and are found in all organs of plant • Can divide and give rise to more specialized cells Collenchyma cells: • Have thicker primary walls • Form bundles underneath epidermis • Provide flexible support for immature regions of the plant 14 Tissues of Flowering Plants Ground tissue (continued) • Sclerenchyma cells: – Have thick secondary walls impregnated with lignin – Most are nonliving – Primary function is to support mature regions of the plant – Two types of sclerenchyma cells » Fibers » Sclereids 15 Ground Tissue Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Parenchyma cells 50 mm 50 mm 50 mm b. Collenchyma cells c. Sclerenchyma cells (All): © Biophoto Associates/Photo Researchers, Inc. 16 Tissues of Flowering Plants • Vascular Tissue Xylem transports water and minerals from the roots to the leaves • Tracheids – Long, with tapered ends – Water moves across pits in end walls and side walls – Vascular rays between rows of tracheids conduct water across the width of the plant • Vessel Elements – Larger, with perforated plates in their end walls – Form a continuous vessel for water and mineral transport 17 Xylem Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. vessel element tracheids xylem parenchyma cell vessel element tracheid perforation plate pitted walls pits 50 mm a. Xylem micrograph (left) and drawing (to side) b. T wo types of vessels c. Tracheids a: © J. Robert Waaland/Biological Photo Service 18 Tissues of Flowering Plants • Vascular Tissue Phloem transports sucrose and other organic compounds from the leaves to the roots • Sieve-tube members function as conducting cells – Contain cytoplasm, but lack nuclei – Sieve plate – cluster of pores in wall • Each sieve-tube member has a companion cell – Plasmodesmata connect the two – Companion cell contains a nucleus 19 Phloem Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. sieve plate sieve-tube member sieve-tube member companion cell companion cell sieve plate nucleus phloem parenchyma cells 20 mm a. Phloem micrograph (left) and drawing (to side) b. Sieve-tube member and companion cells a: © George Wilder/Visuals Unlimited 20 24.3 Organization and Diversity of Roots • Root cap contains root apical meristem • Zone of cell division contains primary meristems • Zone of elongation contains cells that are lengthening and becoming specialized • Zone of maturation contains fully differentiated cells 21 Organization and Diversity of Roots • Tissues of a Eudicot Root: Epidermis - outer layer of root Cortex – composed of parenchyma cells allowing water and minerals movement Endodermis – forms a boundary between cortex and inner vascular cylinder • Casparian strip Vascular Tissue - contains xylem and phloem • Pericycle – mitotically active and can begin development of branch or lateral roots 22 Eudicot Roots Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vascular cylinder endodermis pericycle phloem xylem cortex epidermis root hair 50 µm b. Vascular cylinder phloem endodermis Zone of maturation water and minerals Casparian strip xylem of vascular cylinder pericycle Zone of elongation c. Casparian strip procambium Zone of cell division ground meristem protoderm root apical meristem protected by root cap root cap 23 a. Root tip a: Courtesy Ray F. Evert/University of Wisconsin Madison; b: © CABISCO/Phototake Branching of Eudicot Root Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. epidermis emerging branch root cortex pericycle vascular cylinder endodermis © Dwight Kuhn; 24.10a: © John D. Cunningham/Visuals Unlimited 24 Organization and Diversity of Roots • Monocot roots: Ground tissue of root’s pith is surrounded by vascular ring Have the same growth zones as eudicot roots, but do not undergo secondary growth Have pericycle, endodermis, cortex, and epidermis 25 Monocot Root Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. vascular cylinder a. pith phloem xylem pericycle endodermis cortex epidermis b. 100 mm a: © John D. Cunningham/Visuals Unlimited; b: Courtesy George Ellmore, Tufts University 26 Organization and Diversity of Roots • Primary root (taproot) - Fleshy, long single root, that grows straight down Stores food • Fibrous root system - Slender roots and lateral branches Anchors plant to soil • Adventitious roots - Roots develop from organs of the shoot system instead of the root system Prop roots 27 Organization and Diversity of Roots • Haustoria: Found in parasitic plants Rootlike projections that grow into host plant Make contact with vascular tissue of the host plant and extract water and nutrients • Mycorrhizae: Mutualistic associations between roots and fungi Assist in water and mineral extraction • Root nodules Contain nitrogen-fixing bacteria 28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Root Diversity a. Taproot c. Prop roots ,a type of adventitious root b. Fibrous root system d. Pneumatophores of black mangrove trees e. Aerial roots of English ivy clinging to tree trunks (a): © Dr. Robert Calentine/Visuals Unlimited; (b): © Evelyn Jo Johnson; (c): © David Newman/Visuals Unlimited; (d): © Alan and Linda Detrick/Photo Researchers, Inc.; (e) left: © David Sieren/Visuals Unlimited; (e) right: © Professor David F. Cox, Lincoln Land Community College 29 24.4 Organization and Diversity of Stems • Shoot apical meristem Produces new cells that elongate and increase stem length Protected by terminal bud • Enveloped by leaf primordia • Specialized primary meristems – Protoderm – gives rise to the epidermis – Ground Meristem – gives rise to pith and cortex – Procambium – produces primary xylem and phloem 30 Woody Twig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. bud scale one year's growth lenticel terminal bud internode node node terminal bud scale scars axillary bud stem leaf scar bundle scars 31 Shoot Tip and Primary Meristems Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Three Primary Meristems: protoderm leaf primordium shoot apical meristem protoderm ground meristem procambium ground meristem procambium Primary Tissues internode epidermis axillary bud pith cortex vascular cambium vascular bundles pith primary xylem vascular cambium primary phloem cortex primary xylem primary phloem a. Shoot tip b. Fate of primary meristems 32 Organization and Diversity of Stems • Herbaceous Stems Mature non-woody stems exhibit only primary growth • Outermost tissue covered with waxy cuticle • Stems have distinctive vascular bundles – Herbaceous eudicots - Vascular bundles arranged in distinct ring – Monocots - Vascular bundles scattered throughout stem 33 Herbaceous Eudicot Stem Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. epidermis phloem fiber xylem phloem cortex epidermis pith vascular bundle 100 µm pith vascular cambium 50 µm parenchyma collenchyma Left: © Ed Reschke; Right: Courtesy Ray F. Evert/University of Wisconsin Madison 34 Monocot Stem epidermis ground tissue vascular bundle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ground tissue (parenchyma) xylem phloem bundle sheath cells (Top): © CABISCO/Phototake; (Bottom): © Kingsley Stern vessel element air space sieve-tube member companion cell 35 Organization and Diversity of Stems • Woody Stems Woody plants have both primary and secondary tissues • Primary tissues formed each year from primary meristems • Secondary tissues develop during first and subsequent years from lateral meristems 36 Organization and Diversity of Stems • Woody stems have both primary and secondary growth Primary growth increases the length of the plant Secondary growth increases the girth • Woody stems have no vascular tissue, and instead have three distinct regions Bark Wood Pith 37 Secondary Growth of Stems Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vascular cambium: Lateral meristem that will produce secondary xylem and secondary phloem in each succeeding year. pith primary xylem primary phloem a. b. Periderm: As a stem becomes woody, epidermis is replaced by the periderm. cortex epidermis pith primary xylem secondary xylem vascular cambium secondary phloem lenticel primary phloem cortex cork cambium cork Bark: Includes periderm and also living secondary phloem. Wood: Increases each year; includes annual rings of xylem. c. xylem ray phloem ray secondary xylem vascular cambium secondary phloem cork cambium cork 38 Organization and Diversity of Stems • Bark Bark of a tree contains cork, cork cambium, and phloem Bark can be removed, but it is harmful to the plant due to lack of organic nutrient transport Cork cells are impregnated with suberin • Gas exchange is impeded except at lenticels 39 Organization and Diversity of Stems • Wood Wood is secondary xylem that builds up year after year • Vascular cambium is dormant during winter • Annual ring is made up of spring wood and summer wood In older trees, inner annual rings, called heartwood, no longer function in water transport 40 Three-year-old Woody Twig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. cork cork cambium cortex phloem ray Bark phloem Vascular Cambium summer wood spring wood secondary xylem annual ring Wood primary xylem Pith 41 © Ed Reschke/Peter Arnold, Inc. Tree Trunk Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. annual rings heart wood sap wood vascular cambium phloem cork a. Tree trunk, cross-sectional view b. Tree trunk, longitudinal view a: © Ardea London Limited 42 Organization and Diversity of Stems • Stem Diversity Above ground vertical stems Stolons • Above ground horizontal stems • Produce new plants when nodes touch the ground Rhizomes • Underground horizontal stems • Contribute to asexual reproduction • Variations: – Tubers - Enlarged portions functioning in food storage – Corms - Underground stems that produce new plants during the next season 43 Stem Diversity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. rhizome branch papery leaves axillary bud adventitious roots stolon corm axillary bud node rhizome adventitious roots tuber adventitious roots a. Stolon b. Rhizome c. Tuber d. Corm a: © The McGraw-Hill Companies Inc./Evelyn Jo Johnson, photographer; b: © Science Pictures Limited/Photo Researchers, Inc.; c: © The McGraw Hill Companies, Inc./Carlyn Iverson, photographer; d: © The McGraw Hill Companies, Inc./Carlyn Iverson, photographer 44 24.5 Organization and Diversity of Leaves • Leaves contain: Upper and lower epidermis • Waxy cuticle • Trichomes • Lower epidermis has stomata for gas exchange Mesophyll • Eudicot leaves have – Palisade mesophyll containing elongated cells – Spongy mesophyll containing irregular cells bounded by air spaces • Contains many chloroplasts 45 Leaf Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. trichomes cuticle Water and minerals enter leaf through xylem. upper epidermis palisade mesophyll Sugar exits leaf through phloem. air space bundle sheath cell spongy mesophyll lower epidermis cuticle leaf vein stoma chloroplast central vacuole epidermal cell upper epidermis nucleus chloroplast palisade mesophyll O2 and H2O exit leaf through stoma. nucleus leaf vein guard cell CO2 enters leaf through stoma. mitochondrion spongy mesophyll stoma Leaf cell Stoma and guard cells lower epidermis 100 m SEM of leaf cross section © Jeremy Burgess/SPL/Photo Researchers, Inc. 46 Organization and Diversity of Leaves • Leaf Diversity Blade of a leaf can be simple or compound Leaves are adapted to environmental conditions • Shade leaves • Spines • Climbing leaves 47 Classification of Leaves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. axillary bud Alternate leaves, beech Simple leaf, magnolia axillary buds Palmately compound leaf, buckeye Whorled leaves, bedstraw Pinnately compound leaf black walnut, a. Simple versus compound leaves Opposite leaves, maple b. Arrangement of leaves on stem 48 Leaf Diversity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. stem spine tendril hinged leaves a. Cactus, Opuntia b. Cucumber, Cucumis c. Venuss ’ flytrap, Dionaea a: © Patti Murray Animals Animals/Earth Scenes; b: © Gerald & Buff Corsi/Visuals Unlimited; c: © P. Goetgheluck/Peter Arnold, Inc. 49