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Chapter 24 PLANT STRUCTURE and FUNCTION Reproductive shoot (flower) Overview of PLANT STRUCTURE Terminal bud Node Internode Terminal bud Shoot system Vegetative shoot • Vegetative organs are concerned with growth and nutrition • Flowers, seeds, and fruits are structures involved in reproduction. Leaf Blade Petiole Axillary bud Stem Taproot Lateral roots Root system Flowering Plants: Monocots or Eudicots Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Root Stem Leaf Vascular bundles scattered in stem Leaf veins form a parallel pattern Flower Monocots Seed Root xylem and phloem in a ring Flower parts in threes and multiples of three Eudicots One cotyledon in seed Two cotyledons in seed Root phloem between arms of xylem Vascular bundles in a distinct ring Leaf veins form a net pattern Flower parts in fours or fives and their multiples 10 ROOTS • Roots – Generally, the root system is at least equivalent in size and extent to the shoot system • Anchors plant in soil • Absorbs water and minerals • Produces hormones – Root hairs: • Projections from epidermal root hair cells • Greatly increase absorptive capacity of root 4 Roots 1 • Roots anchor plant in soil, absorb minerals & water, & store food – fibrous roots (1) • mat of thin roots that spread out • monocots – tap roots (2) • 1 large vertical root • also produces many small lateral, or branch roots • dicots – root hairs (3) • increase absorptive surface area 2 3 Shoots • Shoots consist of stems, leaves & buds • Stems – nodes = points at which leaves are attached – internodes = stem segments between nodes • Buds – growth of shoot • terminal or apical bud = at tip of plant • axillary bud = in nodes on stem STEMS – Support for the plant body – Carries nutrients throughout plant – Defense system to protect against predators and infection – Few millimeters to 100 meters LEAVES • Leaves are the major part of the plant that carries on photosynthesis – Foliage leaves are usually broad and thin • Blade - Wide portion of foliage leaf • Petiole - Stalk attaches blade to stem • Leaf Axil - Axillary bud originates – Tendrils - Leaves that attach to objects – Bulbs - Leaves that store 8 food Modified leaves tendrils (peas) succulent leaves spines (cacti) colored leaves (poinsetta) Interdependent systems • Both systems depend on the other sugars – roots receive sugars & other nutrients from photosynthetic parts – shoot system depends on water & minerals absorbed from the soil by roots water Putting it all together • Obtaining raw materials – sunlight • leaves = solar collectors – CO2 • stomates = gas exchange – H2O • uptake from roots – nutrients • uptake from roots • TISSUES OF FLOWERING PLANTS Dermal – “skin” of plant – single layer of tightly packed cells that covers & protects plant • Vascular – transport materials between roots & shoots – xylem & phloem • Ground – everything else: storage, photosynthetic DERMAL TISSUE • Dermal Tissue – Outer covering – Single layer of cells consisting of • Cuticle – waxy coating • Hairs • Guard Cells that surround stomata Cells of GROUND TISSUE Those would’ve been great names for my kids! • Parenchyma – “typical” plant cells = least specialized – photosynthetic cells, storage cells – tissue of leaves, stem, fruit, storage roots • Collenchyma – unevenly thickened primary walls = support • Sclerenchyma – very thick, “woody” secondary walls (lignin) = support – Fibers (rope); Schlereids (grittiness, hardness of nuts, peach pit) – rigid cells that can’t elongate – dead at functional maturity VASCULAR TISSUE • Transports materials in roots, stems & leaves • Xylem – carry water & minerals up from roots – tube-shaped dead cells • only their walls provide a system of microscopic water pipes • Phloem – carry nutrients throughout plant • sugars (sucrose), amino acids… – tube-shaped living cells Xylem • Dead at functional maturity • Cell elongated into tubes – tracheids • long, thin cells with tapered ends • walls reinforced with lignin = support • thinner pits in end walls allows water flow – vessel elements • wider, shorter, thinner walled & less tapered • perforated ends walls allows free water flow from one hole to the next Aaaaah… Structure-Function again! Phloem • Living cells at functional maturity – lack nucleus, ribosomes & vacuole • more room: specialized for liquid food (sucrose) transport • Cells – sieve tubes • end walls, sieve plates, have pores to facilitate flow of fluid between cells, pump sugars – companion cells • nucleated cells connected to the sievetube • Surround sieve tubes; support phloem cells Aaaaah… Structure-Function again! Phloem: food-conducting cells sieve tube elements & companion cells Vascular tissue in herbaceous stems dicot monocot trees & shrubs grasses & lilies • What I should eat…. What I actually eat…. Root structure: dicot phloem xylem Root structure: monocot