Stems BI 103: Plant & Animal A & P Outline: 1. Stems: monocots vs dicots--handout 2. Woody plant growth 3. Discussion problems 4. Monocots & soutside Learning Objectives What are the differences between monocots and dicots? What is the functions of the plant stem? How are specific cells and tissues adapted in the stem in order to help it function? How are tissues in the stem different from the leaves & root? How does the process of transpiration move water through the plant? How does secondary growth occur in woody plants? What are examples of specialized stems? 1
Plant Anatomy: Vegetative Organs Leaves: Photosynthesis Gas exchange Light absorption Stem: Support Transport Storage Roots: Anchorage Storage Transport Absorption Form = Function Tissue Patterns in Stems Cotyledons - Seed leaves attached to embryonic stems Function: Store food needed by young seedling 1. yledons (s) - Flowering plants that develop from seeds having two cotyledons 2. Monocotyledons (Monocots) - Flowering plants that develop from seeds with a single cotyledon 2
Monocot Vascular Number of Leaf Plant Anatomy: Mocot vs. Cotyledons Venation Roots bundle pattern in stem Number of Flower Parts F. B. G. H. D. I. C. E. A. J. Plant Anatomy: Monocot vs. Activity: In lab groups, identify whether each picture is associated with a monocot or dicot. Write number associated with pic in correct column. ~~5 minutes 3
Monocot Vascular Number of Leaf Plant Anatomy: Mocot vs. Cotyledons Venation Roots bundle pattern in stem Number of Flower Parts F. G. B. H. D. I. C. E. A. J. Plant Anatomy: Monocot vs. Monocot Number of Cotyledons Leaf Venation Roots G. Vascular bundle pattern in stem Number of Flower Parts B. D. F. H. I. C. J. E. A. 4
Organs: STEM DICOT MONOCOT Herbaceous Stems Have discrete vascular bundles arranged in a cylinder. 5
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 Typical herb vascular bundle 6
Transpiration Transpiration 7
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. 8
Specialized Stems 3. Stolons Arching stem produced beneath the surface of the ground. Dogwood: Cornus serecia Specialized Stems 4. Corms - Resemble bulbs, but composed almost entirely of stem tissue, with papery leaves Store food Crocus and gladiolus 5. Cladophylls - Flattened, leaf-life stems of cactus Prickly pear cactus 9
1. Primary Growth Stem Growth A. Apical meristem increases length B. Ground meristem makes cortex & pith 2. Secondary growth A. Vascular cambium produces secondary Xylem & Phloem B. Cork cambium produces bark to reduce water loss & protects stem (in woody plants only). Primary vs. Secondary growth Primary Growth All plants Vertical growth up or down Plant gets taller Secondary Growth Woody plants only (only s) Horizontal growth: girth Plant gets wider Where: Meristem tissue in roots & buds Where: vascular cambium, cork cambium 10
Origin and Development of Stems Narrow band of cells between the primary xylem and primary phloem is the vascular cambium. Cells produced by the vascular cambium become the secondary xylem toward center and secondary phloem toward surface. 11
Woody plants Joshua tree (Yucca brevifolia) is NOT a woody plant Think bark because it doesn t have secondary growth! Plants with secondary growth 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 Bundle scars mark food and water conducting tissue within leaf scars. 12