Determinate vs. Indeterminate Growth

4/2/2024 Plant Cells & Tissues Determinate vs. Indeterminate Growth – – Determinate growth: grows to a certain point and then stops (EX: flowers, seeds, fruits) Indeterminate Growth: grows throughout the lifetime of the organism (EX: stems) Groups of Plant Organs – – – – Roots Stems Leaves Flowers (angiosperms only) Organs tissues cells Meristematic Tissues – – Apical meristems Lateral meristems: widening the plant o Cork cambium (dermis/bark) o Vascular cambium (xylem & phloem) Ground Tissues – – – Parenchyma o Most abundant tissue in plants o Cells often have large vacuoles o Function in photosynthesis, storage, & secretion o Aerenchyma & Chlorenchyma Collenchyma o Provides flexible support o Found beneath the epidermis along the veins Sclerenchyma o Provide support & minimize damage from herbivore attacks o Fibers for support and storage o Sclereids – mechanical and protective Rays – lateral conduction of water and nutrients within a woody stem – – – Generally run perpendicular to the xylem and phloem Helps conduct water & nutrients from the xylem and phloem to all the leaves Composed of parenchyma cells Vascular Tissues – – – – Created by vascular cambium in woody plants Created by apical meristems in herbacious plants Xylem composed of parenchyma cells, fibers, vessels, tracheids & ray cells o Tracheids (vascular plants) § Primary and secondary cell walls § Lack protoplasts § Found in all vascular plants § No opening at ends § Dead at maturity o Vessels (gnetophytes & angiosperms) § Primary and secondary cell walls § Lack protoplasts § Found in angiosperms § Perforation (lack the plate/plasmodestama between the primary and secondary cell walls) § Dead at maturity o Both tracheids and vessels have lignin in their cell walls Phloem composed of sieve tube members, companion cells, fibers, parenchyma cells & ray cells o Sieve tube elements § Angiosperms only § Lack secondary cell walls and nuclei § Lay end to end to form sieve tubes § Callose forms callus plug, which prevents leaking of sieve tubes when mechanically damaged § P-proteins (plug proteins); also function as protection when damaged § Living at maturity o Companion cells § Primary cell wall § Closely associated with sieve tube element § Living at maturity o Sieve cells § Gymnosperms only § Primary cell wall in most species § Callose often associated with wall and pores § Lack nucleus and P-protein (plug protein) Transverse view – looking down on the tissue from above Radial view – looking at it being cut in half along a radius Tangenital view – a cut taken from the inside Specialized cells: – – – – Secretory cells Trichomes: hair-like filaments that provide protection against light, UV, or insect/pathogen attack Periderm: replaces the epidermis when cork cambium begins producing new tissues Lenticels: loosely arranged pockets of parenchyma cells that allow for gas exchange 4/4/2024 Roots Taproots vs. Adventitious Roots Taproot: single primary deep root Adventitious roots: develop from stem – – Fibrous roots: Monocots Root Structure – – – – Root cap: thimble-shaped mass of parenchyma cells; protects tissues from damage Cell division area (apical meristem) Cell elongation area (cells start to differentiate) o Vacuoles develop Cell maturation area (cells have completely matured & differentiated) o Root hairs form o Endodermis forms (innermost boundary of the cortex of the ground tissue) § Casparian strip – line of defense o Vascular cylinder – core of tissues inside endodermis § Pericycle – outer boundary of vascular cylinder § Forms lateral roots Symplastic route – through the cells via the plasmodesmata Apoplastic route – around the cells Eudicot Root: Moving Inward Epidermis xylem cortex vascular cylinder endodermis pericycle Casparian strip Monocot Root: Moving Inward Epidermis – cortex – vascular cylinder – endodermis – pericycle Phloem is on the outside of the vascular cambium; xylem is on the inside Mycorrhizal fungi phloem Nitrogen-fixing bacteria Specialized Roots – – – Buttressing roots: grow out and down: have a very large surface area o Provide extra support against the elements & extra water absorption Pnuematophores: absorb oxygen o Contain lenticels for gas exchange Aerial roots: o Epiphytes: plants that grow on other plants, but do not steal nutrients from them