chapter 11 outline
chapter 11 outline BIOL 1110
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This 5 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 15 views. For similar materials see Introduction to Botany in Biology at University of Connecticut.
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Date Created: 01/26/16
Roots and Plant Nutrition 11.1 Roots play a variety of roles in plants Roots anchor plants and absorb water and minerals o First plant organ from seed: embryonic root (radicle) o Primary root system branched root system o Shoot development/photosynthesis depend on water uptake by roots o Branch roots develop when water is available **hormone abscisic acid stops growth until water is available again** o Soil-binding capacity – prevents soil erosion Some roots store carbohydrates o Biennial plants store carbs in fleshy storage roots during 1 st year, food fuels development of flowers, fruits, and seeds during nd 2 year Sites of hormone/secondary compound production o Cytokinin & gibberellin go through xylem to shoot for growth o Secrete secondary compounds to kill bacteria, fungi, survival of the fittest plant competition Some roots support stems o Prop roots grow from above ground stem into soil o Buttress roots – large as a person, above ground o Aerial roots – ropelike roots from branches to soil Pneumatophores provide oxygen to underwater roots of mangroves o Specialized roots of mangrove trees that grow in water o Grow upward into air; absorb oxygen through lenticels – water- repellent surface openings o Contain aerenchyma tissue with air-filled, open channels o O2 generates ATP in roots, needed for nutrient uptake by roots Other specialized roots o Herbaceous plants produce contractile roots – collapse cells to pull shoot deeper for warmth o Parasitic plants obtain materials from host plants o Epiphytic plants grow non-parasitically on other plants 11.2 Taproots, fibrous roots, and feeder roots are major types of underground root formations Differences result from seedling’s primary root Taproot system – single main root from which many branches emerge; long systems lift deep soil water; gymnosperms and eudicot angiosperms Adventitious roots emerge from the surface of a stem; no single root is most prominent; monocots Fibrous system – highly branched & shallower than taproot system o Feeder roots – produced by taproot and fibrous root systems; fine branch roots that absorb water and minerals; very near soil surface but extend far horizontally 11.3 Root external and internal structure are intimately related to function External root structures Branch (lateral) roots – grow from root tip; soiBranc texture influences branching; epidermis and rooth root axis contact soil Emerging branch Root hairs – epidermal cells with long extensions; root main location of water/mineral uptake; near root tip; uptake selectivity Root apical meristem (RAM) – meristematic cells that divide rapidly to increase # cells in main root Root Root cap – generated by & protects RAM hairs o Contains starchrich amyloplasts sense gravity when they fall as root position changes; signal downward growth o Dispersed root cap border cells modify Mucig external root environment; “goalies” Borde el Mucigel – gluey polysaccharide secreted from r cells Golgi apparatus of root tip cells; lubricant helps passage through soil & benefits microbes Root Internal root structures cap RAM produces primary tissues – protoderm, ground meristem, procambium Zone of elongation o Cells from apical meristem elongate by water absorption into vacuole o Cell vacuole enlarges & exerts pressure on cell wall; requires more cytoplasm o Cell specialization begins here; phloem differentiates from procambium early Phloem brings organic material to root cells; its early appearance reflects root tip’s requirement for these materials for high rates of cell division Zone of maturation (specialization) o Procambium vascular tissues in root core o Protoderm root epidermis o Ground meristem cortex – between epidermis and innermost vascular tissues o Epidermis and cortex – absorption of water/minerals Symplastic – uptake into the cytoplasm of root hairs Root hairs absorb minerals through proteins and water by osmosis & aquaporins – increase rate of water absorption Transport proteins bind only to useful minerals Root hair minerals plasmodesmata cytoplasm of cortex Apoplastic – movement through loose cell walls & spaces between epidermis and cortex o Endodermis – filter system between cortex and vascular system Waterproof barrier wrapped in lignin + suberin = Casparian strip Minerals enter nonsuberized regions of endodermis; transport proteins carry useful minerals & reject harmful; minerals taken up by root hairs pass Casparian strip because they’ve been filtered already o Primary vascular system – xylem, phloem, pericyle Pericycle – produces branch roots; retains meristematic activity; cell division here forms vascular cambium Ecological significance of roots Reduce erosion Microbes fix nitrogen for plants Soil minerals Necessary ions: nitrate, phosphate, calcium, iron, copper, manganese, magnesium Many mineral ions – cations that electrostatically bind to negative surface of clay Electrostatic attraction holds cations in soil to reduce mineral loss during rain (leaching) Some ions are harmful (aluminum) Cation exchange – abundant hydrogen ions bind to negative soil particles, which release cations that plant roots can then absorb Chapter Wrap-up Examine and Discuss Self Test 1. Why do roots require oxygen? Oxygen and phosphate generate ATP in roots. 2. What are pneumatophores, what is their function, and what types of plants produce them? Roots specialized to grow under water; capture O2; mangroves produce them 3. Distinguish among taproots, adventitious roots, fibrous roots, and feeder roots. Taproots - one main root with other branch roots; grow really deep down to absorb water Adventitious roots emerge from stem surface; no main root Fibrous roots – equally fine branches with no main root; shallower than taproots Feeder roots – develop from taproot and fibrous root systems; fine branch roots that grow just below surface; extend horizontally; absorb minerals and water 4. Starting at a branch root and ending at the tip of a root, describe the external features that you would see. 5. Considering the internal structure of a root, what three major zones would you encounter? Zones of cell division, elongation, and maturation 6. Explain how root hairs and endodermal cells absorb useful soil minerals. Root hairs Symplastic – absorption through osmosis and mineral transport through proteins into cytoplasm of root xylem Apoplastic – water and minerals flow through intercellular spaces and loose cell walls into cytoplasm of root Casparian strip Endodermal cells – filters fluid between cortex & vascular system with Casparian strip Applying Concepts 1. Imagine that you germinate a seed on a piece of wet filter paper and it sprouts a primary root that is about 2 cm in length. You use an ink pen to place back marks on the root, startingat the tip and marking the root at 1 mm intervals, for a total of about 20 marks. You now allow the root to grow to 5 cm in length. Which areas of the root will not have elongated, so that marks there will still be spaced 1 mm apart? Which areas will have changed their length and hence the spacing between the black marks? Increased spacing closest to apical meristem 2. Why do root hairs occur in the zone of maturation instead of closer to the root tip? They would get destroyed if they had to travel through soil with elongating or dividing cells—zone of maturation is more stable 3. Imagine that you and a friend are in the produce section of a grocery store looking at potatoes. You mention that potatoes are a kind of stem known as a tuber, not roots, even though potatoes grow underground. Your friend disagrees, arguing that potatoes are roots because they grow underground. What evidence could you point to, without cutting or otherwise modifying a potato that would support your case? Sprouts will grow from the buds if it is a stem
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