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

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

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 Dermal Tissue

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

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: TWO MAIN TYPES OF ROOTS: 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 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)

Wood Bark Cork Contains old, nonfunctioning xylem that helps support the tree Contains active xylem that transports water and minerals Produces new xylem and phloem, which increase the width of the stem Transports sugars produced by photosynthesis Produces protective layer of cork Contains old, nonfunctioning phloem that protects the tree Xylem: Heartwood Cork Cambium Phloem Vascular Cambium Xylem: Sapwood

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: C6H12O2) 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 Cuticle Veins Epidermis Palisade mesophyll Xylem Vein Phloem Spongy mesophyll Epidermis Stoma 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

Stomata/Guard Cells Stoma Open Stoma Closed Guard cells Inner cell wall Stoma

Leaf Structure/Function Gas Exchange Leaves take in CO2 and give off O2 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 Cuticle Veins Epidermis Palisade mesophyll Xylem Vein Phloem Spongy mesophyll Epidermis Stoma 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.

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.