Chapter 23

Roots, Stems and Leaves

Section 23-1 Learning Targets

   Describe the organs and tissues of vascular plants Identify the specialized cells of vascular tissue Contrast meristematic tissue with other plant tissues

Specialized Tissues in Plants

 Three main organs of plants :  ROOTS: underground organs that absorb water and minerals  Also anchor the plant and hold it upright   STEMS: supporting structures that connect roots and leaves   Carry water and nutrients Holds leaves up to light LEAVES: carry out photosynthesis  Capture light, flat so cover more surface area  Cuticle and adjustable pores protect leaves from water loss

Tissue Systems

 Within the roots, stems and leaves are FOUR specialized tissue systems:   DERMAL TISSUE: forms the skin of a plant (is the outermost layer of cells) VASCULAR TISSUE: like the plant’s bloodstream (transports water and nutrients throughout the plant)   GROUND TISSUE: cells between the dermal and vascular tissues MERISTEMATIC TISSUE: found only in the tips of shoots and roots

Stem Root Leaf Dermal tissue Vascular tissue Ground tissue Three tissues of plants

Dermal Tissue

  Outer covering of a plant Consists of:   Epidermis: outermost layer Cuticle: thick, waxy layer that protects against water loss and injury (covers epidermis)  On under side of leaves, contains guard cells which regulate water loss and gas exchange

Vascular Tissue

  Transport system: “bloodstream” Consists of xylem and phloem   Xylem: water-conducting tissue  Transports water to leaves Phloem: food-conducting tissue  Takes sugar to the roots

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Ground Tissue

Tissue that lies between dermal and vascular tissue  Consists of parenchyma, collenchyma and sclerenchyma

Meristematic Tissue

  New growth is produced in cells that make up meristematic tissue It is the ONLY plant tissue that produces new cells by mitosis!!

 Best place to see this at the tip of a shoot/root where apical meristem is located

Section 23-2 Roots Learning Targets

   Describe the two main types of roots Identify the tissues and structures in a mature root.

Describe the different functions of roots.

Roots

 Functions:   Absorb water and nutrients Anchor plant  TWO MAIN TYPES OF ROOTS:   Taproots: found mainly in dicots  EX: carrot, dandelions, beets, radishes, oak tree Fibrous Roots: found mainly in monocots   Help to prevent erosion EX: grass

ROOTS

Root Structure

 Epidermis of root is covered with tiny projections called root hairs  Increase surface area of root to absorb more water  Roots grow in length as their apical meristem produces new cells near the root tip  The fragile new cells are covered by a tough root cap that protects the root as it forces its way through soil

Root Function

 Roots anchor the plants into the ground and absorb water and nutrients.

 Roots use osmosis and active transport to move water and nutrients into the plant roots to support the plants growth

Section 23-3 Stems

 Describe the main functions of stems  Contrast monocot and dicot stems  Explain how primary growth and secondary growth occur in stems

Stems

  3 IMPORTANT FUNCTIONS:    Produce Leaves, branches and flowers Hold leaves up in the sunlight Transport substances between roots and leaves Composed of dermal, vascular and ground tissue (like the rest of the plant)

Stem Parts

   Nodes: where leaves are attached Internodes: regions between the nodes Buds: contain undeveloped tissue that can produce new stems and leaves

Monocot v. Dicot Stems

 Moncots: vascular bundles are scattered throughout the stem

Monocot v. Dicot Stems

 Dicots: vascular bundles are arranged in a cylinder

Primary vs. Secondary Growth

 Plants grow in two main ways:  Primary Growth: produced by cell divisions in the apical meristem (tips of roots and shoots)  Secondary Growth: the type of growth in which the stem increases in width.

P R I M A R Y G R O W T H

Secondary Growth:WOOD

 WOOD is actually layers of XYLEM  Heartwood: older xylem in center of wood, that no longer conducts water  Darkens with age as it accumulates impurities  Sapwood: surrounds heartwood, active in transport

WOOD   Growth Rings Indicate age of tree and environmental conditions   Thick rings indicate the growing season experienced adequate moisture Thin rings indicate there was less water (draught)

Xylem: Heartwood

Contains old, nonfunctioning xylem that helps support the tree

Wood Xylem: Sapwood

Contains active xylem that transports water and minerals

Bark Cork

Contains old, nonfunctioning phloem that protects the tree

Cork Cambium

Produces protective layer of cork

Phloem

Transports sugars produced by photosynthesis

Vascular Cambium

Produces new xylem and phloem, which increase the width of the stem

Section 23-4 Leaves

 Describe how the structure of a leaf enables it to carry out photosynthesis  Describe how gas exchange takes place in a leaf

Leaf Structure

  Main organs of photosynthesis  Makes food for plants (glucose: C 6 H 12 O 2 ) Structure is optimized for absorbing light and carrying out photosynthesis  Blades: thin, flattened to increase surface area to absorb sunlight  Attached to stem by petiole   Epidermis: outer layer Cuticle: waxy, protective layer  Protects tissues and limits water loss

Leaf Structure

Leaf Function

 Photosynthesis  Most of photosynthesis carried out in MESOPHYLL layer  Packed with chloroplasts  Palisade Mesophyll: column-shaped cells just under epidermis  Absorb most of light coming into leaf

Leaf Function

Veins Spongy mesophyll Cuticle Epidermis Palisade mesophyll Xylem Phloem Vein Stoma Epidermis Guard cells

Leaf Structure/Function

 Spongy Mesophyll: loose tissue layer beneath palisade with air spaces between cells  Air spaces connect with outside through STOMATA

Leaf Structure/Function

 STOMATA: pores in underside of leaf that let carbon dioxide and oxygen diffuse in and out of the leaf  Each stoma consists of two GUARD CELLS  Guard Cells: cells in the epidermis that control the opening and closing of the stomata by responding to water pressure changes

Single stomata Multiple stomata

Stoma

Stomata/Guard Cells

Guard cells Guard cells Inner cell wall Inner cell wall

Stoma Open Stoma Closed

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Leaf Structure/Function

Gas Exchange   Leaves take in CO 2 and give off O 2 during photosynthesis Plant leaves allow gas exchange by opening their stomata   If kept open all the time, there would be large amounts of water loss due to transpiration Plants keep stomata open just enough to allow photosynthesis to take place, not long enough to lose too much water  Guard cells regulate opening/closing of the stomata   If water pressure is high, they open the stomata If water pressure is low, they close the stoma

Leaf Structure/Function

Veins Spongy mesophyll Cuticle Epidermis Palisade mesophyll Xylem Phloem Vein Stoma Epidermis Guard cells

Section 22-5 Transport in Plants

 Explain how water is transported throughout the plant  Describe how the products of photosynthesis are transported throughout the plant.

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Water Transport

Combo of root pressure, capillary action and transpiration provides force to move water through the xylem    Root Pressure: pressure created by water entering the tissues of a root that pushes water upward in a plant stem Capillary Action: tendency of water to rise in a THIN tube  Water is attracted to the walls of the tube and to other water molecules Transpiration: loss of water through plant leaves by evaporation  When water is lost through transpiration the leaf “pulls” water upward from the roots  Moves water from HIGH to LOW pressure

Water Movement

Evaporation of water molecules out of leaves.

Pull of water molecules upward from the roots.