Chapter 23 Roots, Stems and Leaves

Learning Targets 23.1 What are the principal organs and tissues of vascular plants? How is meristematic tissue different from other plant tissues? What specialized cells make up vascular tissue?

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

Ground Tissue Parenchyma: Collenchyma Thin cell walls and large vacuoles In leaves, these cells are packed with chloroplasts and are the site of photosynthesis Collenchyma Cells with strong, flexible walls that help to support larger plants This is what makes up the stringy part of celery

Ground Tissue Sclerenchyma Cells that have an extremely thick, ridged, cell wall that makes ground tissue tough and strong.

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

Learning Targets 23.2 What are the two main types of roots? What are the main tissues in a mature root? What are 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 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

Learning Targets 23.3 What are the three main functions of stems? How do monocot and dicot stems differ? How do primary growth and secondary growth occur in stems?

Stems 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 Growth For a plant’s entire life, new cells are produced at the tips of roots and shoots This is called primary growth They increase in length It takes place in all seed plants

Secondary Growth The pattern of growth in which stems increase in width is called secondary growth In conifers and dicots, secondary growth takes place in lateral meristematic tissue called the vascular cambium and cork cabium

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

Learning Targets 23.4 How does the structure of a leaf enable it to carry out photosynthesis? How does gas exchange take place in a leaf?

Leaves 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

Leaves

Simple and Compound Leaves

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

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

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

Leaf Structure/Function 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

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

Leaf Structure/Function Cuticle Veins Epidermis Palisade mesophyll Xylem Vein Phloem Spongy mesophyll Epidermis Stoma Guard cells

Learning Targets 23.5 How is water transported throughout a plant? How are the products of photosynthesis transported throughout the plan?

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

Water Transport Transpiration: loss of water through plant leaves 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.