chapter 10 outline
chapter 10 outline BIOL 1110
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This 4 page Class Notes was uploaded by Caitrín Hall on Tuesday January 26, 2016. The Class Notes belongs to BIOL 1110 at University of Connecticut taught by Bernard Goffinet in Summer 2015. Since its upload, it has received 12 views. For similar materials see Introduction to Botany in Biology at University of Connecticut.
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Date Created: 01/26/16
Stems and Materials Transport 10.1 Stems are fundamental plant organs having multiple functions Vascular tissues – xylem and phloem – conduct water, minerals, and organic materials All plants except bryophytes contain vascular systems o Bryophytes lack lignin Stems appeared before roots/leaves o Basis of shoot system o Enable plants to increase height, mass, and surface with apical meristem Apical growth – increased access to sunlight o Transport water and minerals from roots to leaves, conduct sugars from leaves to roots Xylem conducts water, dissolved minerals Lignin – tough & waterproof; in walls of water conductors (tracheids and vessel elements); strengthens walls of fibers that support vascular tissues; constructed of phenolic secondary compounds Phloem transports organic compounds (sugars) in a water solution 10.2 The structure of conducting tissues helps explain their functions Vascular bundles Herbaceous stems have xylem and phloem produced by apical meristems Surrounded by supportive sclerenchyma Separated by varying amounts of parenchyma Mature conducting tissues o Primary phloem Companion cells – necessary for function of sieve elements; retain nuclei & provide materials to sieve elements through plasmodesmata Sieve elements – pipeline components with perforated ends (sieve plates) Pores develop by expansion of plasmodesmata Allow phloem sap to move freely Alive at maturity but lack some components (nucleus +) Conducts sugars from their source to the sites of utilization by a pushing mechanism [Pressure (mass) flow] (guttation) moves compounds through phloem by osmosis o Water flows from xylem to sieve elements with higher sugar concentrations, but rigid cell walls prevent expansion (pressure builds within sieve elements) o Movement of sap requires different sugar concentrations throughout sieve path From source of organic molecules to places that use them (“source to sink”) Symplastic (symplasmic) loading – sucrose is loaded from cells producing them to sieve elements or companion cells to sieve elements **no ATP required** Apoplastic (apoplasmic) loading – sucrose is loaded from intercellular spaces into phloem 1. Parenchyma cells secrete sucrose into intercellular spaces 2. Companion cells import sucrose into their cytoplasm **requires ATP** 3. Sucrose moves through plasmodesmata from companion to sieve o Primary xylem Supplies water necessary for phloem pressure flow Dead tissues facilitate water transport Flowering plants contain elongate cells – narrow tracheids, wide vessel elements Nonflowering primarily use tracheids Differentiation – cytoplasmic death leaves empty cells Tracheids fit together to form pipeline Vessels – stacks of perforated vessel elements Lignin coats sidewalls of tracheids/vessels in ring-like pattern Pits – nonlignified areas in sidewalls; allow water movement Transpiration – evaporation of water from plant surfaces; creates cohesion-tension, which pulls water through xylem Monocots – scattered Dicots – organized in a ring Secondary growth – increase in girth Many gymnosperms and dicot flowering plants Woody plants – secondary growth is extensive; bark-covered surface o Trees – one or few main stems o Shrubs – several to many stems o Lianas – woody vines Produces wood tissue & bark through 2 lateral (secondary) meristems o Vascular cambium – produces wood & inner bark Composed of fascicular and interfascicular cambia Produces secondary xylem (wood) toward stem interior; secondary phloem (inner bark) toward exterior Contains 2 types of cells: Vertically elongate fusiform initials – produce secondary xylem/phloem Cuboidal ray initials – produce vascular rays, which store starch, protein, and lipids & transport food and water laterally between secondary xylem/phloem o Cork cambium – produces parenchyma cells and a protective covering for older woody stems Cork replaces protective role of epidermis Layers of lignin and suberin – phenolic compounds prevent microbial attack while waxes retard water loss Tannins inactivate pathogens Exude gums and latexes Lenticels allow gas exchange Periderm – cork, cork cambium, parenchyma cells Originates in inner bark Plants produce more until visible in outer bark – all tissues outside innermost periderm; dead tissues Chapter Wrap-up Examine and Discuss Self Test 1. Which tissue do people tap in the springtime to produce maple syrup? a. primary xylem b. secondary xylem c. secondary phloem d. vascular cambium e. cork cambium 2. Imagine that you are asked to identify a mystery plant. The first step is to determine whether the plant is a monocot or a dicot by examining a thin slice of the stem. You find that the vascular bundles are scattered through the stem, so you are able to say that the plant is a: a. dicot b. monocot c. either a dicot or a monocot d. neither a dicot nor a monocot 3. What tissue does a vascular cambium produce? a. secondary xylem toward the inside and secondary phloem toward the outside of the stem b. primary xylem toward the inside and primary phloem toward the outside of the stem c. primary xylem toward the outside and primary phloem toward the inside of the stem d. just secondary xylem e. just primary xylem 4. If you cut leafy stems of carnation plants bearing white flowers, then place the cut stems into a vase of pink dye, the flowers will turn pink. The color will change faster if you use a fan to blow air across the emergent portions of stems. What is the process that causes the color change? a. Pink-colored flavonoid pigments are produced in flower petals as a response to stress. b. Evaporative water loss at the stem surface pulls water upward by transpiration. c. Mass flow in the phloem pulls the organic dye upward. d. All of the above are likely to occur under these conditions. e. None of the above is a reasonable explanation. 5. A friend states that plant stems always grow vertically and aboveground, but you argue that exceptions occur in the form of: a. grass rhizomes b. strawberry stolons c. gladiolus corms d. iris rhizomes e. all of the above Applying Concepts 1. Imagine that in hanging a sign you pound a nail into the bark of a 10-m- tall tree. If the nail were initially 2 m above ground level, at approximately what height would you expect to find the nail when the tree reaches 20 m in height? 2m because bark indicates secondary growth, which indicates end of vertical growth 2. What would you expect to be the effect on your ability to identify growth rings of trees when there is little climatic difference throughout the year? Can you think of a location where this might occur regularly? It would be harder because early and late wood would look too similar. Tropical locations exhibit this.