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Chapter 27

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Department
Biology
Course
BI111
Professor
Tristan Long
Semester
Winter

Description
Chapter 27: The Plant Body 27.1 Plant Structure and Growth: An Overview • Photosynthetic shoot system extending upward into the air and a  nonphotosynthetic root system extending down into the soil Growth in Plants  Determinate growth common in animals  Indeterminate growth in plants  Plant grows throughout life  Meristems give rise to plant body  Why would this be adaptive?  Plasticity of growth gives some flexibility since plants cannot move around  Plants grow by:  Increase in number of cells  Increase in size of cells Shoot Systems: Functions  Stems, leaves, buds, flowers  Highly adaptive for photosynthesis & positions flowers for pollination  Vegetative (nonreproductive) shoot  Stem with attached leaves and buds  Bud gives rise to extension of shoot or new, branching shoot  Reproductive shoot  Produces flowers which later develop fruits containing seeds Root Systems: Functions  Usually grows below ground  Anchors plant and supports upright parts  Absorbs water and dissolved minerals from soil  Stores carbohydrates 27.1a Cells of All Plant Tissues Share Some General Features • Organs: body structures that contain two or more types of tissues and have a  definite form and function o Includes leaves, stems, roots • Tissue is a group of cells and intercellular substances that function together in one  or more specialized tasks • Primary cell walls surround the plasma membrane and cell contents(cytoplasm  and organelles) o Made of cellulose • Plasmodesmata is a cytoplasmic connection between adjacent cells that allows  solutes such as amino acids and sugars to move from one cell to the next o Space between primary walls and adjacent cells is filled with  polysaccharide layer called middle lamella • As a plant grows, different types of cells deposit additional cellulose and other  materials inside primary wall, forming secondary cell wall o Contain lignin: makes walls o strong and impermeable to water • the ability of almost any cell to give rise to all other parts of a plant is totipotency o allows plants to heal wounds o one mean of asexual reproduction 27.1b Shoot and Root Systems Perform Different but Integrated Functions • a stem with its attached leaves and buds is a vegetative shoot (nonreproduuctive) • a reproductive shoot produces flowers, which later develop fruits containing seeds 27.1c Meristems Produce New Tissues throughout a Plant’s Life • determinate growth: growing to a certain size and then growth stops • indeterminate growth: growing throughout lives • meristems produce new tissues more or less continuously while the plant is alive 27.1d Meristems Are Responsible for Growth in Both Height and Girth • all plants have apical meristems: clusters of self­perpetuating tissue at the tips of  their buds, stems, and roots • tissues that develop from apical meristems are called primary tissues, and they  make up the primary plant body • growth of the primary plant body is called primary growth • secondary growth originates at cylinders of tissue called lateral meristems and  increases the diameter of older roots and stems • tissues that develop from lateral meristems are secondary tissues Primary Growth  Apical meristems at root and shoot tips  Self-perpetuating clusters of cells  Increases height of shoot, length of roots Secondary Growth (in some species)  Lateral meristems at root and shoot tips  Self-perpetuating cylinder of tissue  Increases diameter of stems and roots Primary Growth and Stems  Primary growth produces primary plant body Derivatives of theApical Meristem: Three Primary Meristems  Protoderm  Produces stem’s epidermis  Procambium  Produces primary xylem and phloem  Ground meristem  Produces ground tissue Modifed Stems Spatial & temporal variation in temperature • Ocean environments are less variable than those on land Primary Growth and Leaves  Leaf Primordia gives rise to leaves 27.1e Monocots and Eudicots Are The Two General Structural Forms of Flowering Plants • eudicots: trees, shrubs, non woody plants • monocots: grasses, lilies, cattails, corn, rice • monocot seeds have one cotyledon, eudicot has two o cotyledon: leaves produced by the embryo 27.1f Flowering Plants Can Be Grouped According to Type of Growth and Lifespan • annuals are herbaceous plants in which the life cycle is completed in one growing  season with minimal or no secondary growth o animals typically only have apical meristems • biennials such as carrots complete their life cycle in two growing seasons and  limited secondary growth occurs in some species • perennials, vegetative growth and reproduction continue year after year 27.2 The Three Plant Tissue Systems • simple tissues have only one type of cell • complex tissues are organized with arrays of two or more types of cells • ground tissue system (makes up most of the plant body) functions in metabolism  (including photosynthesis), storage, and support • vascular tissue system consists of xylem and phloem, which transport water and  nutrients throughout the plant o cylinders of vascular tissue are embedded in ground tissue • dermal tissue system is a shin like protective covering for the plant body Vascular Plant Body  3 Tissue Systems: Ground, Vascular & Dermal  Organ/Tissue system: Body structure that contains two (or more!) types of tissues and have a definite form and function  Tissue: Group of one (or more!) types of cells and intercellular substances that function together in one (or more!) specialized tasks Primary Shoot System  Consists of main stem, leaves, and buds  Plus any attached flowers and fruits  Stems are adapted to provide  Mechanical support  House vascular tissues  Food and water storage  Buds and meristems for growth  Leaves carry out photosynthesis and gas exchange Lignin  Some plant cells have “lignified” secondary cell wall  Cellulose fibres anchored with lignin: stronger and more rigid  Creates waterproof barrier (hydrophobic)  Resistant to decay and attack by microbes Plant Tissue System: Form & Function  3 Tissue Systems: Ground, Vascular & Dermal  Ground tissues are all structurally simple but exhibit important differences  Vascular tissues are specialized for conducting fluids  The dermal tissue system protects plant surfaces Ground, Vascular, and Dermal Tissues 27.2a Ground Tissues Are All Structurally Simple but Exhibit Important Differences • 3 types of tissues: parenchyma, collenchyma, sclerenchyma • parenchyma: soft primary tissues o makes up bulk of primary growth of roots, stems, leaves, flowers, fruits o thin primary wall o permeable to water o large air spaces o storage, secretion, photosynthesis o alive and metabolically active when mature o Thin primary cell walls, pliable and permeable to water, often round o Air spaces (gas exchange, buoyancy) o Specialized for storage, secretion, photosynthesis  They are found in the cortex and pith of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds. o Metabolically active when mature o Capable of additional cellular division (meristematic) if stimulated • collenchyma: flexible support o strings in celery o strengthen plant parts o cellulose and pectin o walls stretch as the cell enlarges, growing organs o alive and metabolically active, continue to synthesize primary wall layers  as the plant grows o Thicker (uneven) primary cell walls (pectin) – especially at the corners o Elongated cells in strands or sheath like cylinder o Not uniformly thick walls o Strengthen plant parts still elongating  Found adjacent to outer growing tissues and the vascular cambium o Metabolically active & meristematic  Additional growth stimulated by mechanical stress • sclerenchyma: rigid support and protection o Thick, uniform, secondary cell walls (hemicelluslose & lignin) o No air spaces between them, large amount of strength o Adding lignin chokes off plants, and thus these cells are terminal o Dead at maturity as cut off from rest of organism o Found in stems, leaf veins and make up the hard outer covering of seeds & nuts. o Two major types  Sclereids (protective casings) • Cells are irregular in shape. Commonly found in fruit and seeds.  Fibres (support) • Cells are often needle-shaped with pointed tips – some elasticity Ground Tissues 27.2b Vascular Tissues Are Specialized for Conducting Fluids • xylem: transporting minerals and water o conducts water and dissolved minerals absorbed from the soil upward  from a plants roots to the shoot o types of conducting cells:  tracheid’s • elongated with tapered, overlapping ends • strong secondary walls to keep plants from collapsing when  water becomes scarce • water can move between through pits o seeps laterally between cells  vessel members • shorter, wider cells joined end to end in tubelike columns  called vessels • have pits • as they mature, enzymes break down portions of their end  walls, producing perforations • moves water more efficiently • phloem: transporting sugars and other solutes o transports solutes and sugars made in photosynthesis through the plant  body o main conducting cells are sieve tube members connected end to end  end walls called sieve plates, are studded with pores  immature sieve tube members contain the usual plant organelles,  but the cell nucleus and internal membranes in plastids break  down, mitochondria shrink, and cytoplasm is reduced to a think  layer lining the interior surface of the cell wall • specialized parenchyma cells known as companion cells are connected to mature  sieve tube members by Plasmodesmata Vascular Tissue: Xylem • Conducts water and dissolved minerals • Thick, lignified secondary walls • Dead when functional Types of Xylems: Tracheids and Vessel Members Tracheids • Elongated, tapered, overlapping ends • Lateral connections through pits Vessel members • Shorter, tubelike columns • Lateral connections through pits and perforations • Vessel members are better at quickly moving water, more easily blocked by air bubbles in water Vascular Tissue: Phloem • Conduct sugars and other solutes • Living* when functional Sieve Tube Members  Joined end to end in sieve tubes  Sieve tube cells assisted by “companion cells”  Parenchyma cells that load and unload organic compounds into sieve tube  End walls (sieve plates) studded with pores 27.2c The Dermal Tissue System Protects Plant Surfaces • epidermis covers primary plant body in single continuous layer or multiple layers  of packed cells • external surface of epidermal cell walls is coated with waxes that are embedded in  cutin, a network of chemically linked fats • epidermal cells secrete cuticle which resists water loss and helps protect against  attacks by microbes • guard cells contain chloroplasts and so can carry out photosynthesis o pore between guards is stomata
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