Biology, 9th ed, Sylvia Mader Chapter 25 Chapter 25 Structure and Organization of Plants Plant Structure and Organization

Outline Plant Organs Roots Stems Monocots vs. Eudicots Leaves Epidermal Tissue Vascular Tissue Roots Organization Diversity Stems Leaves

Plant Organs Roots Generally, the root system is at least equivalent in size and extent to the shoot system Anchors plant in soil Absorbs water and minerals Produces hormones Root hairs: Projections from epidermal root hair cells Greatly increase absorptive capacity of root

Organization of Plant Body

Vegetative Organs of Several Eudicots

Shoot system of a plant is composed of the stem, branches, and leaves Stems Shoot system of a plant is composed of the stem, branches, and leaves Stem is the main axis of a plant that elongates and produces leaves Nodes occur where leaves are attached to the stem Internode is region between nodes Stem also has vascular tissue that transports water and minerals

Leaves are the major part of the plant that carries on photosynthesis Foliage leaves are usually broad and thin Blade - Wide portion of foliage leaf Petiole - Stalk attaches blade to stem Leaf Axil - Axillary bud originates Tendrils - Leaves that attach to objects Bulbs - Leaves that store food

Monocots (Single cotyledon) Monocot vs. Eudicot Monocots (Single cotyledon) Cotyledons act as transfer tissue Root vascular tissue occurs in ring Parallel leaf venation Eudicots (Two cotyledons) Cotyledons supply nutrients to seedlings Root phloem located between xylem arms Netted leaf venation

Flowering Plants: Monocots or Eudicots

Plant Tissues Epidermal Tissues Contain closely packed epidermal cells Covered with waxy cuticle Roots contain root hairs Lower leaf surface contain stomata Woody plants covered by cork

Modifications of Epidermal Tissue

Ground tissue forms bulk of a plant Parenchyma cells: Least specialized and are found in all organs of plant Can divide and give rise to more specialized cells Collenchyma cells: Have thicker primary walls Form bundles underneath epidermis Flexible support to immature regions of the plant

Ground Tissue Cells

Ground Tissue Sclerenchyma cells: Have thick secondary walls impregnated with lignin Most are nonliving Primary function is to support mature regions of the plant Fibers Sclereids

Xylem transports water and minerals from the roots to the leaves Vascular Tissue Xylem transports water and minerals from the roots to the leaves Tracheids Long, with tapered ends Pits in end walls Vascular rays Fibers Vessel Elements Larger, with perforated plates in their end walls

Xylem Structure

Ground Tissue Sclerenchyma cells: Have thick secondary walls impregnated with lignin Most are nonliving Primary function is to support mature regions of the plant Fibers Sclereids

Vascular Tissue Phloem transports sucrose and other organic compounds from the leaves to the roots Sieve-tube members are conducting cells Contain cytoplasm but no nuclei Channels in end walls Plasmodesmata extend from one cell to another through sieve plate

Phloem Structure

Primary meristems are in the zone of cell division Organization of Roots Root apical meristem Located in the root tip Protected by root cap Primary meristems are in the zone of cell division Zone of maturation contains fully differentiated cells

Tissues of Eudicot Root Epidermis Cortex Endodermis Casparian Strip Vascular Tissue Pericycle

Eudicot Roots

Branching of Eudicot Root

Organization of Monocots Roots Monocot roots: Ground tissue of root’s pith is surrounded by vascular ring Have the same growth zones as eudicot roots, but do not undergo secondary growth

Monocot Root

Fibrous root system - Slender roots and lateral branches Root Diversity Primary root (taproot) - Fleshy, long single root, that grows straight down Stores food Fibrous root system - Slender roots and lateral branches Anchors plant to soil Adventitous roots - Roots develop from organs of the shoot system Prop roots

Root nodules - Contain nitrogen-fixing bacteria Root Diversity Haustoria: Rootlike projections that grow into host plant Make contact with vascular tissue and extract water and nutrients Mycorrhizas: Associations between roots and fungi Assist in water and mineral extraction Root nodules - Contain nitrogen-fixing bacteria

Root Diversity

Organization of Stems Shoot apical meristem Produces new cells that elongate and increase stem length Protected by terminal bud Enveloped by leaf primordia Specialized primary meristems Protoderm Ground Meristem Procambium

Woody Twig

Shoot tip and Primary Meristems

Mature nonwoody stems exhibit only primary growth Herbaceous Stems Mature nonwoody stems exhibit only primary growth Outermost tissue covered with waxy cuticle Stems have distinctive vascular bundles Herbaceous eudicots - Vascular bundles arranged in distinct ring Monocots - Vascular bundles scattered throughout stem

Herbaceous Eudicot Stem

Monocot Stem

Woody plants have both primary and secondary tissues Woody Stems Woody plants have both primary and secondary tissues Primary tissues formed each year from primary meristems Secondary tissues develop during first and subsequent years from lateral meristems

Woody Stems Woody stems have no vascular tissue, and instead have three distinct regions Bark Wood Pith

Secondary Growth of Stems

Bark of a tree contains cork, cork cambium, and phloem Bark can be removed, but it is harmful to the plant due to lack of organic nutrient transport Cork cells are impregnated with suberin Gas exchange is impeded except at lenticels

Wood is secondary xylem that builds up year after year Vascular cambium dormant during winter Annual ring is made up of spring wood and summer wood In older trees, inner annual rings, heartwood, no longer function in water transport

Three-year-old Woody Twig

Tree Trunk

Stem Diversity Stolons: Rhizomes: Above-ground horizontal stems Produce new plants when nodes touch the ground Rhizomes: Underground horizontal stems Contribute to asexual reproduction Variations: Tubers - Enlarged portions functioning in food storage Corms - Underground stems that produce new plants during the next season

Stem Diversity

Blade of a leaf can be simple or compound Leaf Diversity Blade of a leaf can be simple or compound Leaves are adapted to environmental conditions. Shade leaves Spines Climbing leaves

Leaf Structure

Classification of Leaves

Leaf Diversity

Review Plant Organs Roots Stems Monocots vs. Eudicots Leaves Epidermal Tissue Vascular Tissue Roots Organization Diversity Stems Leaves

Biology, 9th ed, Sylvia Mader Chapter 25 Ending Slide Chapter 25 Structure and Organization of Plants Plant Structure and Organization