1. CHAPTER 32 Plant Nutrition and Transport

2. Plants That Clean Up Poisons
This healthy fern, pictured with University of Florida researcher Lena Ma, contains high levels of arsenic
Arsenic is a chemical element toxic to most plants and animals

3. Plants like this are commonly known as “metal accumulators”
They are able to absorb large amounts of lead, zinc, and other heavy metals
Unable to move about in search of food, plants have adapted to survive in the presence of toxins

4. Metal accumulators can be used in phytoremediation
the use of plants to help clean up polluted soil and groundwater

5. Sunflowers have been used to clean up radioactive wastes
Sunflowers were set adrift on foam rafts in a pond near the destroyed nuclear power plant in Chernobyl to absorb strontium-90 and cesium-137

6. Although phytoremediation has had some successes, it does pose several problems
Disposal of plants that have accumulated the toxic substances
Evaporation of accumulated toxic substances into the air
Animal ingestion of toxin-laden plants
The length of time it takes for the plants to reduce soil toxicity

7. 32.1 Plants acquire their nutrients from soil and air
THE UPTAKE AND TRANSPORT OF PLANT NUTRIENTS
32.1 Plants acquire their nutrients from soil and air
As a plant grows, its roots absorb water, minerals (inorganic ions), and some oxygen from the soil
Its leaves take carbon dioxide from the air
Figure 32.1A

8. Photosynthesis makes use of the uptake of water, carbon dioxide, and minerals to produce sugars
These sugars are composed of carbon, oxygen, and hydrogen
The nitrogen and magnesium absorbed from the soil are components of chlorophyll
Phosphorus, also absorbed from the soil, is a major component of nucleic acids, phospholipids, and ATP

9. The ability to move water from roots to leaves and to deliver sugars to specific areas of the body are remarkable feats of evolutionary engineering
Figure 32.1B

10. 32.2 The plasma membranes of root cells control solute uptake
Root hairs greatly increase a root's absorptive surface
Figure 32.2A

11. In order for upward transport, water and solutes must enter the xylem
Water and solutes move through the root's epidermis and cortex by two main routes
Through cells (intracellular route)
Between cells (extracellular route)
Water and solutes typically follow a combination of routes and passages through numerous plasma membranes and cell walls en route to the xylem

12. Epidermis
Cortex
Phloem
Root hair
Xylem
Casparian strip
Endodermis
Casparian strip
Xylem
EXTRACELLULAR ROUTE, via cell walls; stopped by Casparian strip
Root hair
INTRACELLULAR ROUTE, via cell interiors; through plasmodesmata
Epidermis
Cortex
Endodermis
Figure 32.2B

13. The Casparian strip stops water and solutes from entering the xylem via cell walls
Thus water and ions that travel the extracellular route can enter the xylem only by crossing a plasma membrane into an endodermal cell

14. 32.3 Transpiration pulls water up xylem vessels
Xylem sap is the solution of inorganic nutrients conveyed in xylem tissue from a plant's roots to its shoots
Root pressure can push xylem sap up only a few meters
Solute transport raises water pressure in the xylem
Plants pull xylem sap upward from the soil through the transpiration-cohesion-tension mechanism

15. Transpiration is the loss of water from the leaves
It exerts a pull on the xylem sap
Cohesion causes water molecules to stick together
It relays the pull of transpiration along a string of water molecules all the way to the roots
The adhesion of water molecules to xylem cell walls helps counter the effect of gravity

16. Figure 32.3

17. 32.4 Guard cells control transpiration
Guard cells surrounding stomata in the leaves control transpiration
The opening and closing of stomata is an adaptation to help plants regulate their water content and adjust to changing environmental conditions
Guard cells
H2O
H2O
H2O
H2O
H2O
H2O K+
H2O
Vacuole
H2O
H2O
H2O
Stoma opening
Stoma closing
Figure 32.4

18. 32.5 Phloem transports sugars
While xylem sap flows upwards from the roots, phloem sap moves throughout the plant in various directions
The main function of phloem is to transport the sugars made by photosynthesis

19. Phloem contains food-conducting cells arranged end-to-end as tubes
Sieve- tube member
Sieve plate
Figure 32.5A

20. Phloem transports food molecules made by photosynthesis by a pressure-flow mechanism
Sugar is loaded into a phloem tube at the sugar source, raising the solute concentration inside the tube
Figure 32.5B

21. Sugar and water leave the tube at the sugar sink
Water is drawn into the tube by osmosis, raising the pressure in the tube
Sugar and water leave the tube at the sugar sink
Figure 32.5B

22. The increase in pressure at the sugar source and decrease at the sugar sink causes phloem sap to flow from source to sink
Figure 32.5B

23. Plant biologists have used aphids to study phloem sap
These studies have supported the pressure-flow model
Honeydew droplet
Stylet of aphid
Figure 32.5C

24. PLANT NUTRIENTS AND THE SOIL
32.6 Plant health depends on a complete diet of essential inorganic nutrients
A plant must obtain nutrients from its surroundings
Macronutrients, such as carbon, oxygen, nitrogen, and phosphorus, are needed in large amounts
They are used to build organic molecules
Figure 32.6B

25. Micronutrients, including iron, copper, and zinc, act mainly as cofactors or enzymes
Growing plants in solutions of known composition enables researchers to determine nutrient requirements
Hydroponic culture
Complete solution containing all minerals (control)
Solution lacking potassium (experimental)
Figure 32.6A

26. Stunting, wilting, and color changes indicate nutrient deficiencies
32.7 Connection: You can diagnose some nutrient deficiencies in your own plants
Stunting, wilting, and color changes indicate nutrient deficiencies
Compared to the healthy tomato plant on the left, the plant on the right is not getting enough nitrogen
Figure 32.7A, B

27. Phosphorus deficiency is sometimes indicated by a purplish leaf color
Yellow leaves can result from potassium deficiency
Figure 32.7C, D

28. Fertile soil contains a mixture of small rock and clay particles
32.8 Soil contains rock particles, humus, organisms, water, and crucial solutes
Soil characteristics determine whether a plant will be able to obtain the nutrients it needs to grow
Fertile soil contains a mixture of small rock and clay particles
They hold water and ions and allow oxygen to diffuse into plant roots

29. Humus is decaying organic material
It provides nutrients, holds water and air, and supports the growth of organisms that enhance soil fertility

30. Soil horizons are distinct layers of soil
Horizon A, or topsoil, contains rock particles (sand and clay), humus, and living organisms
Horizon B contains fine clay particles and nutrients that have drained down from Horizon A
Horizon C is composed mainly of partially broken-down rock
Figure 32.8A

31. A plant's root hairs are in direct contact with the water that surrounds the tiny particles of topsoil
The root hairs take up dissolved oxygen, ions, and water from the film of soil water that surrounds them
Soil particle surrounded by film of water
Root hair
Water
Air space
Figure 32.8B

32. Anions, such as nitrate (NO3-), are readily available to plants because they are not bound to soil particles
But they tend to drain out of the soil quickly
This reduces soil fertility

33. Cations, such as Ca2+ and Mg2+, adhere to soil particles
In cation exchange, root hairs release H+ ions, which displace cations from soil particles
The root hairs then absorb the free cations K+ K+ K+
Clay particle K+ H+ K+ K+ K+ K+
Root hair
Figure 32.8C

34. 32.9 Connection: Soil conservation is essential to human life
Good soil management includes
water-conserving irrigation
erosion control
the prudent use of herbicides and fertilizers
Figure 32.9A, B

35. 32.10 Connection: Organic farmers avoid the use of commercial chemicals
Organic farmers rely on the principles of ecology rather than the use of synthetic chemicals or pesticides that can damage the environment
Organic farmers try to restore as much to the soil as is drawn from it
Figure 32.10

36. 32.11 Fungi help most plants absorb nutrients from the soil
Relationships with other organisms help plants obtain nutrients
Many plants form mycorrhizae
A network of fungal threads increases a plant's absorption of nutrients and water
The fungus receives some nutrients from the plant
Figure 32.11

37. 32.12 The plant kingdom includes parasites and carnivores
Some plants have evolved parasitic ways of obtaining food from other plants
Dodder obtains organic molecules from other plant species using specialized roots that tap into the host’s vascular tissue
Figure 32.12A

38. Mistletoe supplements its diet by siphoning sap from the vascular tissue of its host plants
Figure 32.12B

39. Carnivorous plants obtain some of their nutrients from animal tissues
The sundew and Venus flytrap use insects as a source of nitrogen
This nutritional adaptation enables them to thrive in highly acidic soil
Figure 32.12C, D

40. 32.13 Most plants depend on bacteria to supply nitrogen
Plants cannot use atmospheric nitrogen, gaseous N2, although it is very plentiful
Instead, nearly all plants depend to some extent on nitrogen supplies in the soil

41. Bacteria in the soil convert N2 from the air and nitrogen compounds from decomposing organic matter into forms that plants can take up and use
Nitrate ions (N03-) and ammonium ions (NH4+)

42. Nitrogen-fixing bacteria
This process of converting atmospheric nitrogen to ammonium is called nitrogen fixation
ATMOSPHERE N2
Amino acids N2
Nitrogen-fixing bacteria
NH4+
Soil
NH4+ (ammonium)
NO3– (nitrate)
Nitrifying bacteria
Ammonifying bacteria
Organic material
Root
Figure 32.13

43. 32.14 Legumes and certain other plants house nitrogen-fixing bacteria
Legumes and certain other plants have nodules in their roots that contain nitrogen-fixing bacteria
Shoot
Nodules
Roots
Figure 32.14A

44. Most of the nitrogen-fixing bacteria in legume nodules belong to the genus Rhizobium
The relationship between the plant and the nitrogen-fixing bacteria is mutually beneficial
Bacteria within vesicle
Figure 32.14B

45. PLANT NUTRIENTS AND AGRICULTURE
Connection: A major goal of agricultural research is to improve the protein content of crops
Plants are the main nutritional source for most people in the world
Therefore, improving the protein content of crops is an important research goal
Figure 32.15A

46. One of the most promising lines of agricultural research is directed toward improving the output of the Rhizobium bacteria that inhabit the root nodules of legumes
Rhizobium DNA
Genes for nitrogen fixation
TURN OFF GENES
Nitrogen compounds in root nodules
Nitrogen-fixing enzymes
Nitrogen fixation N2
Figure 32.15B

47. 32.16 Connection: Genetic engineering is increasing crop yields
Using both gene guns and plasmids for gene transfer, researchers are developing new varieties of crop plants
Gunpowder
Gun
“Bullet”
Plant cells
DNA-coated pellets
Figure 32.16