Chapter 36
Transport in Vascular Plants
Teaching Objectives
An Overview of Transport Mechanisms in Plants
1. Describe how proton pumps function in transport of materials across plant membranes, using the terms proton gradient, membrane potential, cotransport, and chemiosmosis.
2. Define osmosis and water potential. Explain how water potential is measured.
3. Explain how solutes and pressure affect water potential.
4. Explain how the physical properties of plant cells are changed when the plant is placed into solutions that have higher, lower, or the same solute concentration.
5. Define the terms flaccid, plasmolyze, turgor pressure, and turgid.
6. Explain how aquaporins affect the rate of water transport across membranes.
7. Name the three major compartments in vacuolated plant cells.
8. Distinguish between the symplast and the apoplast.
9. Describe three routes available for lateral transport in plants.
10. Define bulk flow and describe the forces that generate pressure in the vascular tissue of plants.
11. Relate the structure of sieve-tube cells, vessel cells, and tracheids to their functions in bulk flow.
Absorption of Water and Minerals by Roots
12. Explain what routes are available to water and minerals moving into the vascular cylinder of the root.
13. Explain how mycorrhizae enhance uptake of materials by roots.
14. Explain how the endodermis functions as a selective barrier between the root cortex and vascular cylinder.
Transport of Xylem Sap
15. Describe the potential and limits of root pressure to move xylem sap.
16. Define the terms transpiration and guttation.
17. Explain how transpirational pull moves xylem sap up from the root tips to the leaves.
18. Explain how cavitation prevents the transport of water through xylem vessels.
19. Explain this statement: “The ascent of xylem sap is ultimately solar powered.”
The Control of Transpiration
20. Explain the importance and costs of the extensive inner surface area of a leaf.
21. Discuss the factors that may alter the stomatal density of a leaf.
22. Describe the role of guard cells in photosynthesis-transpiration.
23. Explain how and when stomata open and close. Describe the cues that trigger stomatal opening at dawn.
24. Explain how xerophytes reduce transpiration.
25. Describe crassulacean acid metabolism and explain why it is an important adaptation to reduce transpiration in arid environments.
Translocation of Phloem Sap
26. Define and describe the process of translocation. Trace the path of phloem sap from a primary sugar source to a sugar sink.
27. Describe the process of sugar loading and unloading.
28. Define pressure flow. Explain the significance of this process in angiosperms.
Student Misconceptions
1. Water potential is a difficult concept for many students. Remind students that water potential is a measure of the potential energy of water relative to the potential energy of pure, free water that is not bound to solutes or surfaces. Return to explanations of potential energy and explain that the potential energy of water refers to water’s ability to perform work as it moves to a state of lower free energy.
2. Students may be confused about the mechanism of stomatal opening and closing. Stomata open when guard cells become turgid and close when guard cells are flaccid. Students may come to your course with the mistaken notion that this is because the cell walls of guard cells are thickened on the side of the stomatal opening and that the thinner walls bow out when the guard cells become turgid to close the stomata. Address this misunderstanding before discussing the role of the cellulose microfibrils in the guard cell walls. These microfibrils resist stretching and compression in the direction parallel to their orientation, causing the guard cells to increase more in length than in width as turgor increases. Because the two guard cells are attached at their tips, the increase in length causes buckling.
3. Some students may be confused if they construct their own analogies between animal circulation and plant transport. Some of the terminology of plant transport—vascular tissue, veins, bleeding of cut stems––can encourage such analogies. These students may develop mistaken notions about exchange of materials between phloem and xylem, and may not appreciate that xylem flow is unidirectional and that most of the water pulled up from the roots is lost through the leaves.
Chapter Guide to Teaching Resources
Overview: Pathways for survival
Concept 36.1Physical forces drive the transport of materials in plants over a range of distances
Transparencies
Figure 36.2 An overview of transport in a vascular plant (layer 1)
Figure 36.2 An overview of transport in a vascular plant (layer 2)
Figure 36.2 An overview of transport in a vascular plant (layer 3)
Figure 36.2 An overview of transport in a vascular plant (layer 4)
Figure 36.3 Proton pumps provide energy for solute transport
Figure 36.4 Solute transport in plant cells
Figure 36.5 Water potential and water movement: An artificial model
Figure 36.6 Water relations in plant cells
Figure 36.8 Cell compartments and routes for short-distance transport
Instructor and Student Media Resources
Video: Plasmolysis
Video: Turgid Elodea
Concept 36.2Roots absorb water and minerals from the soil
Transparency
Figure 36.9 Lateral transport of minerals and water in roots
Concept 36.3Water and minerals ascend from roots to shoots through the xylem
Transparencies
Figure 36.12 The generation of transpirational pull in a leaf
Figure 36.13 Ascent of xylem sap
Student Media Resource
Activity: Transport of xylem sap
Concept 36.4Stomata help regulate the rate of transpiration
Transparency
Figure 36.15 The mechanism of stomatal opening and closing
Student Media Resource
Investigation: How is the rate of transpiration calculated?
Concept 36.5Organic nutrients are translocated through the phloem
Transparencies
Figure 36.17 Loading of sucrose into phloem
Figure 36.18 Pressure flow in a sieve tube
Student Media Resource
Activity: Translocation of phloem sap
For additional resources such as digital images and lecture outlines, go to the Campbell Media Manager or the Instructor Resources section of www.campbellbiology.com.
Key Terms
active transport
apoplast
aquaporin
bulk flow
Casparian strip
chemiosmosis
circadian rhythm
cotransport
endodermis
flaccid
guttation
megapascal (MPa)
membrane potential
mycorrhizae
osmosis
osmotic potential
passive transport
plasmolyze
pressure potential (CP)
proton pump
root pressure
solute potential (CS)
sugar sink
sugar source
symplast
tonoplast
transfer cell
translocation
transpiration
transport protein
turgid
turgor pressure
vacuolar membrane
water potential
wilting
xerophyte
Word Roots
apo- 5 off, away; -plast 5 formed, molded (apoplast: in plants, the nonliving continuum formed by the extracellular pathway provided by the continuous matrix of cell walls)
aqua- 5 water; -pori 5 a pore, small opening (aquaporin: a transport protein in the plasma membranes of a plant or animal cell that specifically facilitates the diffusion of water across the membrane)
chemo- 5 chemical (chemiosmosis: the production of ATP using the energy of hydrogen-ion gradients across membranes to phosphorylate ADP)
circa- 5 a circle (circadian rhythm: a physiological cycle of about 24 hours, present in all eukaryotic organisms, that persists even in the absence of external cues)
co- 5 together; trans- 5 across; -port 5 a gate, door (cotransport: the coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient)
endo- 5 within, inner; -derm 5 skin (endodermis: the innermost of the three primary germ layers in animal embryos)
gutt- 5 a drop (guttation: the exudation of water droplets caused by root pressure in certain plants)
mega- 5 large, great (megapascal: a unit of pressure equivalent to 10 atmospheres of pressure)
myco- 5 a fungus; -rhizo 5 a root (mycorrhizae: mutualistic associations of plant roots and fungi)
osmo- 5 pushing (osmosis: the diffusion of water across a selectively permeable membrane)
sym- 5 with, together (symplast: in plants, the continuum of cytoplasm connected by plasmodesmata between cells)
turg- 5 swollen (turgor pressure: the force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis)
xero- 5 dry; -phyto 5 a plant (xerophytes: plants adapted to arid climates)Instructor’s Guide for Campbell/Reece Biology, Seventh EditionChapter 36Transport in Vascular PlantsInstructor’s Guide for Campbell/Reece Biology, Seventh EditionChapter 36Transport in Vascular PlantsInstructor’s Guide for Campbell/Reece Biology, Seventh Edition