Transcript Chapter 32
Chapter 32 Plant Nutrition and Transport PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants That Clean Up Poisons • Some plants have evolved the ability to take up toxins from the soil • Dr. Lena Ma studies certain species of ferns that are able to absorb and thrive on the poison arsenic • Phytoremediation uses plants to help clean up polluted soil and groundwater – Problems, such as disposal, remain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE UPTAKE AND TRANSPORT OF PLANT NUTRIENTS 32.1 Plants acquire their nutrients from soil and air • Roots absorb water, minerals, and some O2 from the soil • Leaves absorb CO2 from the air • Photosynthesis uses carbon, oxygen, and hydrogen to construct sugars and other organic materials the plant needs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Cellular respiration breaks down sugars, producing O2 and energy • Plants have adapted to transport nutrients from roots to leaves and sugars to specific areas Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-1a CO2 O2 Minerals H2O 32.2 The plasma membranes of root cells control solute uptake • A plant can absorb enough water and inorganic ions through its roots to survive and grow – Root hairs greatly expand surface area for absorption Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Substances enter roots in solution • Water and solutes can move through the root's epidermis and cortex by two routes – Intracellular: via cell interiors, through plasmodesmata – Extracellular: via cell walls; stopped by Casparian strip – Plants usually use a combination of both Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Water and solutes must cross a plasma membrane to enter the xylem for transport upward – Controls solutes that enter xylem Animation: Transport in Roots Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-2b Root hair Epidermis Cortex Phloem Key Dermal tissue system Ground tissue system Vascular tissue system Xylem Casparian strip Endodermis Casparian strip Extracellular route, via cell walls; stopped by Casparian strip Root hair Plasmodesmata Intracellular route, via cell interiors, through plasmodesmata Endodermis Epidermis Cortex Xylem 32.3 Transpiration pulls water up xylem vessels • Xylem sap travels from roots to top of plant through the tracheids and vessel elements in xylem • Root pressure can push sap up a few meters • Most sap is pulled up by the transpirationcohesion-tension mechanism – Transpiration • Loss of water from plant's aerial parts • Aided by two properties of water: cohesion, adhesion Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-3-3 Xylem sap Mesophyll cells Air space within leaf Stoma Outside air Transpiration Adhesion Cell wall Water molecule Cohesion and adhesion in the xylem Xylem cells Cohesion, by hydrogen bonding Root hair Soil particle Water Water uptake from soil Animation: Transpiration Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 32.4 Guard cells control transpiration • Plants can lose water through transpiration • Leaf stomata help plants regulate their water content – Opened and closed by flanking guard cells • Controlled by movement of H2O and K+ – Generally stay open during the day, allowing for entry of CO2 for photosynthesis – Stay closed at night, conserving water – Respond to cues from sunlight, CO2 level, biological clock Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-4 Stoma Guard cells K+ Vacuole Stoma opening Stoma closing Video: Plasmolysis Video: Turgid Elodea Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 32.5 Phloem transports sugars • Phloem contains food-conducting sieve-tube members that transport phloem sap • Phloem sap is transported from sugar source to sugar sink by a pressure-flow mechanism – At the source, sugar is loaded into the phloem by active transport – Water follows by osmosis, raising the water pressure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – At the sink, sugar leaves the phloem – Water follows by osmosis, lowering the water pressure – Water is recycled from the sink to the sugar source through the xylem • Biologists have used aphids to study phloem sap Animation: Translocation of Phloem Sap in Summer Animation: Translocation of Phloem Sap in Spring Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-5a Sievetube member TEM 2,700 Sieve plate LE 32-5b High sugar concentration High water pressure Sugar source Phloem Xylem Sugar Water Source cell Sieve plate Sugar sink Sink cell Sugar Water Low sugar concentration Low water pressure LE 32-5c Honeydew droplet Aphid feeding on a small branch Stylet of aphid Aphid’s stylet inserted into a phloem cell Severed stylet dripping phloem sap PLANT NUTRIENTS AND THE SOIL 32.6 Plant health depends on a complete diet of essential inorganic nutrients • Plants survive and grow solely on inorganic nutrients • Essential elements are those 17 a plant must obtain to complete its life cycle – 9 macronutrients needed in large amounts • Mostly build organic molecules – 8 micronutrients needed in small amounts • Act mainly as enzyme cofactors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-6 Complete solution containing all minerals (control) Solution lacking potassium (experimental) CONNECTION 32.7 You can diagnose some nutrient deficiencies in your own plants • Soil deficient in essential nutrients can produce plants of lower quality • Plants are most commonly deficient in nitrogen, phosphorus, and potassium • Symptoms of many nutrient deficiencies are often distinct enough to identify visually Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 32.8 Fertile soil supports plant growth • Fertile soil contains a mixture of small rock and clay particles – Holds water and ions – Allows O2 to diffuse into plant roots Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Soil structure is categorized according to horizons – A horizon (topsoil) • Rock particles, living organisms, humus; subject to extensive weathering – B horizon • Fewer organisms, less organic matter; less subject to weathering – C horizon • Broken-down rock that has been only slightly weathered Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-8a A B C • Root hairs take up certain inorganic particles by cation exchange – Hairs are in direct contact with water films on soil particles – Ca2+, Mg2+, K+ adhere tightly to soil particles – H+ released into soil solution by root hairs displaces them • Can then be absorbed – Anions less tightly bound to soil particles • More readily available, but may leach from soil Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-8b Soil particle surrounded by film of water Root hair Water Air space LE 32-8c K+ K+ K+ Clay particle H+ K+ K+ K+ K+ K+ Root hair Animation: How Plants Obtain Minerals from Soil Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 32.9 Soil conservation is essential to human life • Three critical areas of good soil management – Proper irrigation • Drip irrigation uses less water than flood irrigation, reduces water loss from evaporation and drainage – Erosion control • Windbreaks, crop terracing, contoured cultivation can prevent loss of soil Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Prudent fertilization • Organic fertilizers or conservative use of chemical fertilizers keep nutrients from building up and polluting water Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 32.10 Organic farmers must follow ecological principles • Organic farmers aim to protect the environment while meeting demand for food • U.S. organic farmers must follow strict guidelines – Protect biological diversity – Maintain and replenish soil fertility – Manage pests without pesticides – Avoid genetically modified organisms – Use few or no synthetic fertilizers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 32.11 Agricultural research is improving the yields and nutritional values of crops • The majority of the world's people depend mainly on plants for protein • Genetic modification holds great potential for creating more nutritious plants – Example: golden rice • Genetic engineering also has potential problems – GM plants may overgrow native species Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PLANT NUTRITION AND SYMBIOSIS 32.12 Fungi help most plants absorb nutrients from the soil • Most plants form mycorrhizae, mutually beneficial associations with fungi – Fungus obtains sugar from host plant – Plant benefits from increased surface area for nutrient and water absorption • Mycorrhizae are an early adaptation that may have helped plants colonize land • Farmers can combat plant malnutrition by inoculating seeds with fungal spores Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 32.13 Most plants depend on bacteria to supply nitrogen • Soil bacteria convert nitrogen to forms plants can use – Nitrogen-fixing bacteria convert atmospheric N2 to ammonia (NH3) – Ammonifying bacteria decompose organic matter, producing ammonium (NH4+) – Nitrifying bacteria convert NH4+ to nitrate NO3Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-13 ATMOSPHERE N2 Amino acids, etc. N2 Nitrogen-fixing bacteria Soil NH3 Organic material Ammonifying bacteria NH4+ H+ NH4+ (ammonium) Nitrifying bacteria NO3 (nitrate) Root 32.14 Legumes and certain other plants house nitrogen-fixing bacteria • Legume-family plants have a symbiotic relationship with nitrogen-fixing bacteria – Rhizobium live in vesicles in root nodules – Plant provides bacteria with carbohydrates and other organic compounds – Bacteria have enzymes that catalyze conversion of N2 to NH4+ – Can increase fertility of soil as well as nourish plant Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 32-14a Shoot Nodules Roots LE 32-14b TEM 5,850 Bacteria within vesicle 32.15 The plant kingdom includes parasites and carnivores • Some plants have evolved ways of obtaining nutrients from other plants or animals – Parasites tap into host plant's vascular system – Carnivores kill and digest insects and other small animals Video: Sun Dew Trapping Prey Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings