Chapter 32

1. Chapter 32 Plant Nutrition and Transport

2. 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

5. 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

6. Cellular respiration breaks down sugars, producing O2 and energy • Plants have adapted to transport nutrients from roots to leaves and sugars to specific areas

7. LE 32-1a CO2 O2 Minerals H2O

9. 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

11. 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

12. Water and solutes must cross a plasma membrane to enter the xylem for transport upward • Controls solutes that enter xylem Animation: Transport in Roots

13. LE 32-2b Root hair Epidermis Cortex Phloem Key Dermal tissue system Ground tissue system Vascular tissue system Casparian strip Xylem Endodermis Casparian strip Extracellular route, via cell walls; stopped by Casparian strip Xylem Root hair Plasmodesmata Intracellular route, via cell interiors, through plasmodesmata Endodermis Epidermis Cortex

14. 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 transpiration-cohesion-tension mechanism • Transpiration • Loss of water from plant's aerial parts • Aided by two properties of water: cohesion, adhesion

15. LE 32-3-3 Xylem sap Mesophyll cells Air space within leaf Stoma Outside air Adhesion Transpiration Cell wall Water molecule Flow of water Xylem cells Cohesion, by hydrogen bonding Cohesion and adhesion in the xylem Root hair Soil particle Water Water uptake from soil

16. Animation: Transpiration

17. 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

18. LE 32-4 Stoma Guard cells K+ Vacuole Stoma opening Stoma closing

19. Video: Plasmolysis Video: Turgid Elodea

20. 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

21. 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

22. LE 32-5a Sieve- tube member Sieve plate TEM 2,700

23. LE 32-5b Phloem Xylem High sugar concentration Sugar High water pressure Sugar source Water Source cell Sieve plate Sink cell Sugar sink Sugar Water Low sugar concentration Low water pressure

24. LE 32-5c Stylet of aphid Honeydew droplet LM 760 Severed stylet dripping phloem sap Aphid feeding on a small branch Aphid’s stylet inserted into a phloem cell

25. 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

26. LE 32-6 Complete solution containing all minerals (control) Solution lacking potassium (experimental)

27. 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

33. 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

34. 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

35. LE 32-8a A B C

36. 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

37. LE 32-8b Soil particle surrounded by film of water Root hair Water Air space

38. LE 32-8c K+ K+ K+ Clay particle H+ K+ K+ K+ K+ K+ Root hair

39. Animation: How Plants Obtain Minerals from Soil

40. 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

41. Prudent fertilization • Organic fertilizers or conservative use of chemical fertilizers keep nutrients from building up and polluting water

44. 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

46. 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

48. 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

50. 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 NO3-