Chapter 23 Roots Stems and Leaves Learning Targets

Chapter 23 Roots, Stems and Leaves

Learning Targets 23. 1 l What are the principal organs and tissues of vascular plants? l How is meristematic tissue different from other plant tissues? l What specialized cells make up vascular tissue?

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

Tissue Systems l 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

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

Dermal Tissue l Outer covering of a plant l 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” l Consists of xylem and phloem ¡ Xylem: water-conducting tissue l Transports water to leaves ¡ Phloem: food-conducting tissue l Takes sugar to the roots l

Ground Tissue l Tissue that lies between dermal and vascular tissue ¡ Consists of parenchyma, collenchyma and sclerenchyma

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

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

Meristematic Tissue l New growth is produced in cells that make up meristematic tissue l 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 l What are the two main types of roots? l What are the main tissues in a mature root? l What are the different functions of roots?

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

ROOTS

Root Structure l Epidermis of root is covered with tiny projections called root hairs ¡ l 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 l What are three main functions of stems? l How do monocot and dicot stems differ? l How do primary growth and secondary growth occur in stems?

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

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

Monocot v. Dicot Stems l Moncots: vascular bundles are scattered throughout the stem

Monocot v. Dicot Stems l Dicots: vascular bundles are arranged in a cylinder

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

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

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

Learning Targets 23. 4 l How does the structure of a leaf enable it to carry out photosynthesis? l How does gas exchange take place in a leaf?

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

Leaves

Simple and Compound Leaves

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

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

Leaf Structure/Function l 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 Phloem Vein Spongy mesophyll Epidermis Stoma Guard cells

Leaf Structure/Function l 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 l 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 l 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 l Plants keep stomata open just enough to allow photosynthesis to take place, not long enough to lose too much water l

Leaf Structure/Function ¡ Guard cells regulate opening/closing of the stomata If water pressure is high, they open the stomata l If water pressure is low, they close the stoma l

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

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

Learning Targets 23. 5 l How is water transported throughout a plant? l How are the products of photosynthesis transported throughout the plan?

Water Transport l 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 l Water is attracted to the walls of the tube and to other water molecules

Water Transport l 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.