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Stems BI 103:Dynamic plant Outline: 1. Announcements 2. Root review 3. Stems: monocots vs dicots 4. Woody plant growth Announcements Homework: Root coloring due today Wed: Lab on plant stems Friday: Tree
Stems BI 103:Dynamic plant Outline: 1. Announcements 2. Root review 3. Stems: monocots vs dicots 4. Woody plant growth Announcements Homework: Root coloring due today Wed: Lab on plant stems Friday: Tree rings activities Homework 4: coloring stems due next week 1. How do monocot roots differ from dicot roots? 2. What is an example of a specialized root and what is it used for? Organs: ROOT **Discuss with a partner** ~ 3 min DICOT MONOCOT Specialized Roots Specialized Roots Aerial Roots Orchids - Velamen roots, with epidermis several layers thick to reduce water loss Corn - Prop roots support plants in high wind Ivies (English ivy, Virginia creeper) - Aerial roots aid plants in climbing Orchid aerial (velamen) roots o Contractile Roots Pull plant deeper into the soil Lilly bulbs, dandelions Buttress Roots Stability in shallow soil Tropical Trees Parasitic Roots Buttress roots of tropical fig tree No chlorophyll and dependent on chlorophyll-bearing plants for nutrition 1 Pneumatophores In plants with roots growing in water Spongy roots that extend above the water s surface and enhance gas exchange between atmosphere and subsurface roots Specialized Roots Mangrove pneumatophores Plant Anatomy: Vegetative Organs Leaves: Photosynthesis Gas exchange Light absorption Roots: Anchorage Absorption Stem: Support Form = Function Plant Organs: Objectives Compare and contrast tissues & cells in stems, roots, and leaves in relation to their functions Monocots vs. dicots Identify and describe the structures and functions of different cell and tissue type in organs: stems leaves Roots Tissue Patterns in Stems Cotyledons - Seed leaves attached to embryonic stems Function: Store food needed by young seedling 1. Dicotyledons (Dicots) - Flowering plants that develop from seeds having two cotyledons 2. Monocotyledons (Monocots) - Flowering plants that develop from seeds with a single cotyledon Organs: STEM Herbaceous Dicot Stems Have discrete vascular bundles arranged in a cylinder. Vascular cambium arises between primary xylem and primary phloem. - Adds secondary xylem and secondary phloem DICOT MONOCOT Dic ot ste 2 Tissue Patterns in Stems - Monocots Have neither a vascular cambium nor a cork cambium. Produce no secondary vascular tissues or cork Primary xylem and phloem in discrete vascular bundles scattered throughout the stem Vascular bundles oriented with xylem closer to center of stem and phloem closer to surface. Parenchyma (ground tissue) surrounds vascular bundles. Cross section of monoco stem Tissue Patterns in Stems - Monocots In a typical monocot vascular bundle: Two large vessels with several small vessels First formed xylem cells stretch and collapse. Leave irregularly shaped air space Phloem consists of sieve tubes and companion cells. Vascular bundle surrounded by sheath of sclerenchyma cells. Monocot vascular bundle Transpiration and cohesion tension theory How Materials move in the Xylem Method by which water moves from the roots to the shoot system through the xylem. Loss of water out of stomata by evaporation. Hydrogen bonds link water molecules together. Water moves up and the xylem in a long chain. Water molecules pull each other up one molecule at a time from previous location below. Column of water is under tension. - Cohesion Water Stress Occurs when a break in the water chain contained in the xylem vessel elements breaks. May occur: When transpiration rates increase During very hot, dry weather Note- Extreme wilting can kill the plant. of Sugars Sugars flow from: Source (leaf) Sink Sink = any structure that uses up sugars or stores them e.g. fruits, roots, stems. Pressure-flow theory relies on differential hydrostatic pressure to move fluid through the phloem cells. 3 Specialized Stems: Rhizome 1. Rhizome: underground stem Ferns Potatoes Ginger Specialized Stems: Runners 2. Runners: Horizontal stems that grow above ground and have long internodes. Specialized Stems 3. Stolons - Produced beneath the surface of the ground and tend to grow in different directions. Dogwood: Cornus serecia Specialized Stems 4.Tubers - Swollen, fleshy, underground stem Store food Potatoes - Eyes of potato are nodes 5. Bulbs - Large buds surrounded by numerous fleshy leaves, with a small stem at lower end Store food Onions, lilies, hyacinths, tulips Specialized Stems 6. Corms - Resemble bulbs, but composed almost entirely of stem tissue, with papery leaves Store food Crocus and gladiolus 7. Cladophylls - Flattened, leaf-life stems of cactus Prickly pear cactus 4 Stem Growth 1. Primary Growth A. Apical meristem increases length B. Ground meristem makes cortex & pith 2. Secondary growth A. Procambium produces primary Xylem & Phloem B. Vascular cambium produces secondary Xylem & Phloem C. Cork cambium/phellogen produces bark to reduce water loss & protects stem (in woody plants only). Formation of Vascular Tissues in Woody Plants Secondary meristem Increase Girth 1) Vascular cambium: generates vascular tissues. 2) Cork cambium: generates protective outer covering, including bark. Elements: Fusiform initials Generates secondary Ph & Xy Ray initials Vascular rays (for lateral transport) Origin and Development of Stems Narrow band of cells between the primary xylem and primary phloem may become vascular cambium. Cells produced by the vascular cambium become components of secondary xylem toward center and secondary phloem toward surface. Woody plants Joshua tree (Yucca Plants brevifolia) with secondary is growth NOT a woody plant Think bark because it doesn t have secondary growth! External Form of A Woody Twig Axil - Angle between petiole and stem - Axillary Bud located in axil. Will become branches or flowers in flowering plants Bud scales protect buds. Terminal Bud at twig tip - Growth makes twig longer. - Number of groups of bud scale scars tells age of twig. Stipules - Paired, often leaflike appendages at base of a leaf 5 External Form of A Woody Twig Deciduous trees and shrubs (lose all leaves annually) - After leaves fall, have dormant axillary buds with leaf scars below Plant Anatomy: Vegetative Organs Leaves: Photosynthesis Gas exchange Light absorption Stem: Support Bundle scars mark food and water conducting tissue within leaf scars. Roots: Anchorage Absorption Form = Function Discuss with a partner 1. What structural features in the stem enable it to provide support for the plant? 2. How does the internal anatomy of stems allow them to transport water and nutrients? 3. What features of the stem allow for food storage? Wednesday Lab Stem lab exercise 9 pgs Pre-lab assignment: Pg. 69 Bring in a woody twig 6
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