Plant Structure, Growth & Development: Overview of Roots, Stems, Leaves & Tissue Systems, Slides of Biology

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Chapter 35 Plant Structure, Growth, and Development Docsity.com Plant Structure • The plant body has a hierarchy of organs, tissues, and cells • Plants, like multicellular animals, have organs composed of different tissues, which are in turn composed of cells • The basic morphology of vascular plant reflects their evolutionary history as terrestrial organisms that draw nutrients from two different environments: below-ground (water and minerals) and above-ground (carbon dioxide and light) Docsity.com Roots • In most plants – The absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the root Docsity.com 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 Docsity.com Buds • An axillary bud – Is a structure that has the potential to form a lateral shoot, or branch • A terminal bud – Is located near the shoot tip and causes elongation of a young shoot Docsity.com Leaves (use in classification) • In classifying angiosperms – Taxonomists may use leaf morphology as a criterion Docsity.com Leaves-modified • Some plant species – Have evolved modified leaves that serve various functions Tendrils Spines Storage leaves Bracts Reproductive leaves Docsity.com The Three Tissue Systems: Dermal, Vascular, and Ground • Each plant organ – Has dermal, vascular, and ground tissues Docsity.com Common Types of Plant Cells • Like any multicellular organism – A plant is characterized by cellular differentiation, the specialization of cells in structure and function Docsity.com • Some of the major types of plant cells include – Parenchyma (perform most metabolic functions of the plant such as photosynthesis) – Collenchyma (provide flexible support) – Sclerenchyma (provide more rigid support…contain lignin) – Water-conducting cells of the xylem – Sugar-conducting cells of the phloem Docsity.com • Parenchyma, collenchyma, and sclerenchyma cells Docsity.com Growth • In woody plants primary and secondary growth occur simultaneously but in different locations Each year apical meristems produce young extensions of roots and shoots, while lateral meristems produce secondary growth that thickens and strengthens older plant areas. Docsity.com Primary growth lengthens roots and shoots • Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems Docsity.com Primary Growth of Roots • The root tip is covered by a root cap, which protects the delicate apical meristem as the root pushes through soil during primary growth Docsity.com Primary Growth of Shoots • A shoot apical meristem – Is a dome-shaped mass of dividing cells at the tip of the terminal bud – Gives rise to a repetition of internodes and leaf-bearing nodes Docsity.com Tissue Organization of Stems • In gymnosperms and most eudicots – The vascular tissue consists of vascular bundles arranged in a ring Docsity.com • In most monocot stems – The vascular bundles are scattered throughout the ground tissue, rather than forming a ring Docsity.com The Vascular Cambium and Secondary Vascular Tissue • The vascular cambium – Is a cylinder of meristematic cells one cell thick – Develops from parenchyma cells – Gives rise to secondary xylem and phloem tissues Docsity.com • Viewed in cross section, the vascular cambium – Appears as a ring, with interspersed regions of dividing cells called fusiform initials and ray initials Docsity.com Heartwood…Sapwood 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 Docsity.com The Plane and Symmetry of Cell Division • The plane (direction) and symmetry of cell division are important in determining plant form • If the planes of division of cells are parallel to the plane of the first division a single file of cells will be produced Docsity.com • If the planes of division vary randomly – Asymmetrical cell division occurs Docsity.com • The plane in which a cell divides – Is determined during late interphase • Microtubules in the cytoplasm – Become concentrated into a ring called the preprophase band Docsity.com • Polarity – Is one type of positional information • In the gnom mutant of Arabidopsis – The establishment of polarity is defective Docsity.com • Morphogenesis in plants, as in other multicellular organisms – Is often under the control of homeotic genes (master regulatory genes of development) Docsity.com Cellular Differentiation • In cellular differentiation – Cells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genome – A cell’s position in a developing organ may determine its pathway of differentiation Docsity.com • The most obvious morphological changes – Typically occur in leaf size and shape Docsity.com Genetic Control of Flowering • Flower formation – Involves a phase change from vegetative growth to reproductive growth – Is triggered by a combination of environmental cues and internal signals • The transition from vegetative growth to flowering is associated with the switching-on of floral meristem identity genes Docsity.com • Plant biologists have identified several organ identity gene that regulate the development of floral pattern – The ABC model of flower formation-Identifies how floral organ identity genes direct the formation of the four types of floral organs Docsity.com