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  • Roots, Stems and Leaves

    Chapter 23: Biology II

  • Structure of Seed Plants

    Roots

    Stems

    Leaves

  • Roots

    Branching networks in the soil

    Absorb water

    Dissolve nutrients from moist

    soil

    Anchor plants in the ground

    Hold plants upright

  • Stems

    Supports the plant body

    Transports nutrients within the

    plant

    Tall stems hold leaves up to the

    sun, up to 100 m tall

    Vascular tissues within supply the

    plant with water and nutrients

  • Leaves

    Principal organs for

    photosynthesis

    Broad, flat surface

    increases SA for sunlight

    absorption

    Adjustable pores conserve

    water and allow for the

    exchange of gases

  • Tissue Systems Meristematic

    The only plant tissue that produces new cells by mitosis

    All the cells of a plant originate in meristems and look alike

    Divides into the 3 main tissues

    Dermal

    skin

    Vascular

    bloodstream

    Ground

    everything else

  • Meristematic Tissue

    Found in several places in a plant

    Apical Meristem: found at the tip of each growing stem and root

  • Dermal Tissue

    The outer covering of a plant

    Epidermal Cells in non-woody plants

    Cuticle: thick, waxy covering that protects against water loss and injury

    Trichomes: tiny cellular projections which help protect the leaf and give it a fuzzy appearance

    Root Hair Cells

    Guard Cells: underside of leaves

  • Vascular Tissue

    Transports water and nutrients throughout

    the plant

    Xylem: water-conducting tissue

    Phloem: food-conducting tissue

  • Xylem: Tracheids

    Found in seedless vascular plants and gymnosperms

    Long, narrow cells with walls impermeable to water

    Have openings that connect neighboring cells to one another

    Mature and die; their cytoplasm disintegrates

  • Xylem: Vessel Elements Found in angiosperms

    Wider than tracheids

    Arranged end to end, on top of each other, like a stack of tin cans

    When the cell dies the cell walls at the end die, making one long tube

  • Phloem: Sieve Tube Elements

    Cells arranged end to end to form sieve tubes

    The end walls have many holes in them

    As the mature, they lose most nuclei and organelles; the space becomes a pipeline for sugar and other foods to be carried

  • Phloem: Companion Cells

    Surround sieve tube elements

    Keep their nuclei and other

    organelles throughout their lifetime

    Support the phloem cells

    Aid in the movement of substances

    in and out of the phloem stream

  • Ground Tissue

    The cells between dermal and vascular tissues

  • Ground Tissue: Parenchyma

    Thin cell wall

    Large central vacuole

    Site of the most of a

    plants photosynthesis

  • Ground Tissue: Collenchyma

    Strong, flexible cell wall

    Helps support larger

    plants

    Example: the strings of

    a stalk of celery

  • Ground Tissue: Sclerenchyma

    Extremely thick, rigid

    cell wall

    Makes ground tissue

    tough and strong

  • Types of Roots: Taproots

    Found mainly in dicots

    Primary root grows long and thick

    Secondary roots remain small

    Long taproots: Oak trees, hickory trees,

    Short taproots: carrots, dandelions, beets, etc.

  • Types of Roots: Fibrous Roots

    Found mainly in monocots

    Branch to such an extent that

    no single root grows larger

    than the rest

    Helps prevent topsoil from

    being washed away by heavy

    rain

  • Root Structure and Growth

  • Root Root Hairs: Tiny projections from the

    outer surface, or epidermis, of a root

    Cortex: Spongy layer of ground tissue just

    inside the epidermis of a root

    Endodermis: Layer of cells that

    completely encloses vascular cambium

    Vascular Cylinder/Cambium: Central

    region of a root that includes the vascular

    tissue-xylem and phloem

    Root Cap: Tough structure that protects a

    root as it forces its way through the soil

  • Root: Functions

    Uptake of plant nutrients

    Active transport of minerals: requires ATP!

    Movement into the vascular cylinder: Casparian strip: waterproof strip that surrounds plant endodermis cells

    Root pressure

  • Stem Structure and Function

    Produce leaves, branches and flowers

    Hold leaves up in the sunlight

    Transport substances between roots and leaves

  • Stem Structure and Function

    Node: point on a stem where a leaf is attached

    Internode: region between nodes on plant stems

    Bud: plant structure containing undeveloped tissue that can produce new stems and leaves

  • Monocot and Dicot Stems

    Monocot Stems: vascular bundles are scattered throughout the

    stem

    Dicot Stems (and most gymnosperms): vascular bundles are

    arranged in

    a cylinder

    Pith: parenchyma

    cells inside the ring

    of vascular tissue in

    dicot stems

  • Growth of Stems

    Primary Growth: Type of plant growth that occurs at the

    tips of roots and shoots

    Cell divisions in the apical meristem

    Takes place in all seed plants

    Secondary Growth: Pattern of plant growth in which stems

    increase in width

    Enables the plant to support more weight and more fluid through

    the vascular tissues

  • Formation of the Vascular Cambium

    New layers of vascular tissue are created each year after secondary growth begins

    New meristematic tissue forms between the xylem an phloem of each vascular bundle

    Divisions in the vascular cambium give rise to new layers of xylem and phloem

  • Formation of Wood

    Most of what we call wood is actually layers of xylem

    Heartwood: older xylem near the center of a woody stem that no longer conducts water; darkens with age

    Sapwood: area in plants that surrounds heartwood and is active in fluid transport; lighter in color

    Heartwood and sapwood make up tree rings

  • Formation of Bark

    Tree structure that includes all tissues outside the vascular cambium, including phloem, the cork cambium, and cork

  • Leaf Structure and Functions

    Optimized for absorbing light and carrying out photosynthesis

    Blade: thin, flattened section of a plant leaf that collects sunlight

    Petiole: thin stalk by which a leaf blade is attached to a stem

    Photosynthesis

    Transpiration

    Gas Exchange

  • Water Transport in Plants

    Root pressure

    Capillary Action

    Transpiration

    Together provide enough force to move water

    through the xylem tissue of even the largest plant!

  • Capillary Action

    Tendency of water to rise in

    a thin tube

    Adhesion: attraction

    between unlike molecules

  • Transpiration

    The evaporation of water from leaves

    Controlled by the guard cells

    The biggest contributor to moving water in the plant

  • Nutrient Transport

    Water is pulled upward in plants; nutrients are pushed through phloem

    Phloem: In cold climates, sugar is stored in the roots in the winter and in the trunk and branches in the springhow does it move?

  • Movement from Source to Sink

    Pressure-Flow Hypothesis: When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in that same direction

    As a result, phloem is able to move nutrients in either direction to meet the nutritional needs of the plant