Plant Structure - Fundametnals of Biology - Lecture Notes, Study notes of Biology

Download Plant Structure - Fundametnals of Biology - Lecture Notes and more Study notes Biology in PDF only on Docsity! 1 1 Chapter 35 Plant Structure, Growth, and Development 2 Concept 35.1: The plant body has a hierarchy of organs, tissues, and cells • Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells • Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below ground and above ground 3 • Three basic organs evolved: roots, stems, and leaves • They are organized into a root system and a shoot system • Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system 4 5 Roots • Roots are multicellular organs with important functions: – Anchoring the plant – Absorbing minerals and water – Storing organic nutrients 6 • A taproot system consists of one main vertical root that gives rise to lateral roots, or branch roots • Adventitious roots arise from stems or leaves • Seedless vascular plants and monocots have a fibrous root system characterized by thin lateral roots with no main root 7 8 9 Stems • A stem is an organ consisting of – An alternating system of nodes, the points at which leaves are attached – Internodes, the stem segments between nodes 10 • An axillary bud is a structure that has the potential to form a lateral shoot, or branch • An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot • Apical dominance helps to maintain dormancy in most nonapical buds 11 12 Leaves • The leaf is the main photosynthetic organ of most vascular plants Chapter 35 - Plant Structure, Growth and Development Docsity.com 2 • Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem 13 • Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves – Most monocots have parallel veins – Most eudicots have branching veins • In classifying angiosperms, taxonomists may use leaf morphology as a criterion 14 15 16 Dermal, Vascular, and Ground Tissues • Each plant organ has dermal, vascular, and ground tissues • Each of these three categories forms a tissue system 17 18 • In nonwoody plants, the dermal tissue system consists of the epidermis • A waxy coating called the cuticle helps prevent water loss from the epidermis • In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots • Trichomes are outgrowths of the shoot epidermis and can help with insect defense 19 • The vascular tissue system carries out long-distance transport of materials between roots and shoots • The two vascular tissues are xylem and phloem • Xylem conveys water and dissolved minerals upward from roots into the shoots • Phloem transports organic nutrients from where they are made to where they are needed 20 • The vascular tissue of a stem or root is collectively called the stele • In angiosperms the stele of the root is a solid central vascular cylinder • The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem 21 • Tissues that are neither dermal nor vascular are the ground tissue system • Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex • Ground tissue includes cells specialized for storage, photosynthesis, and support 22 Common Types of Plant Cells • Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function 23 Chapter 35 - Plant Structure, Growth and Development Docsity.com 5 epidermis • The innermost layer of the cortex is called the endodermis 44 45 46 47 48 49 Primary Growth of Shoots • A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip • Leaves develop from leaf primordia along the sides of the apical meristem • Axillary buds develop from meristematic cells left at the bases of leaf primordia 50 51 Tissue Organization of Stems • Lateral shoots develop from axillary buds on the stem’s surface • In most eudicots, the vascular tissue consists of vascular bundles that are arranged in a ring 52 53 • In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring 54 55 Tissue Organization of Leaves • The epidermis in leaves is interrupted by stomata, which allow CO2 exchange between the air and the photosynthetic cells in a leaf • Each stomatal pore is flanked by two guard cells, which regulate its opening and closing • The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis 56 • Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll, where gas exchange occurs • The vascular tissue of each leaf is continuous with the vascular tissue of the stem • Veins are the leaf’s vascular bundles and function as the leaf’s skeleton • Each vein in a leaf is enclosed by a protective bundle sheath 57 Chapter 35 - Plant Structure, Growth and Development Docsity.com 6 58 Concept 35.4: Secondary growth adds girth to stems and roots in woody plants • Secondary growth occurs in stems and roots of woody plants but rarely in leaves • The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium • Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots 59 The Vascular Cambium and Secondary Vascular Tissue • The vascular cambium is a cylinder of meristematic cells one cell layer thick • It develops from undifferentiated parenchyma cells 60 • In cross section, the vascular cambium appears as a ring of initials • The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside 61 • Secondary xylem accumulates as wood, and consists of tracheids, vessel elements (only in angiosperms), and fibers • Early wood, formed in the spring, has thin cell walls to maximize water delivery • Late wood, formed in late summer, has thick-walled cells and contributes more to stem support • In temperate regions, the vascular cambium of perennials is dormant through the winter 62 63 64 • Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age • Dendrochronology is the analysis of tree ring growth patterns, and can be used to study past climate change 65 66 • As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals • The outer layers, known as sapwood, still transport materials through the xylem • Older secondary phloem sloughs off and does not accumulate 67 68 The Cork Cambium and the Production of Periderm • The cork cambium gives rise to the secondary plant body’s protective covering, or periderm • Periderm consists of the cork cambium plus the layers of cork cells it produces • Bark consists of all the tissues external to the vascular cambium, including secondary Chapter 35 - Plant Structure, Growth and Development Docsity.com 7 phloem and periderm • Lenticels in the periderm allow for gas exchange between living stem or root cells and the outside air 69 Chapter 35 - Plant Structure, Growth and Development Docsity.com