Transport

1. Transport Processes

2. Fig 36.2

3. I. Membrane Transport A. Passive Transport 1. Mechanisms 2. Requirements

4. Fig 36.7

5. B. Active Transport 1. Mechanisms 2. Requirements

6. B. WhyTransport? 1. Occur at virtually every level of biological organization. 2. Enzymes transport electrons, protons, acetyl groups. 3. Membranes transport material across themselves. 4. Cells transport material to and from other cells, and within themselves. 5. Whole organisms transport water, etc from one organ to another

7. II. Transport in Plants A. Background 1. Plants adapted to the division of resources in the land environment (soil & air) by the differentiation of the plant body into roots and shoots. 2. But this created a new dilemma, the need to transport materials between roots and shoots. 3. Sometimes up to 100m away, in all kinds of environmental conditions. 4. What’s a poor plant to do?

8. B. Three levels of transport in plants: 1. Cellular – uptake of H2O and solutes by individual cells. 2. Short-distance - between cells 3. Long-distance – throughout whole plant (xylem & phloem) 4. Scenarios and Terms

9. 0 An artificial cell consisting of an aqueous solution enclosed in a selectively permeable membrane has just been immersed in a beaker containing a different solution. The membrane is permeable to water and to the simple sugars glucose and fructose but completely impermeable to the disaccharide sucrose.

10. a. sucrose b. glucose c. fructose 0 Which solute(s) will exhibit a net diffusion into the cell?

11. 0 Which solute(s) will exhibit a net diffusion out of the cell? a. sucrose b. glucose c. fructose

12. 0 • Which solution is hypertonic to the other? • the cell contents • the environment

13. 0 • In which direction will there be a net osmotic • movement of water? • out of the cell • into the cell • neither

14. 0 • After the cell is placed in the beaker, which of the • following changes will occur? • The artificial cell will become more flaccid. • The artificial cell will become more turgid.

15. III. Water Potential A. Definition Water potential refers to the free energy of water, its capacity to do work. By definition pure free water has a water potential of zero. B. Factors 1. Increased heating, pressure, or elevation 2. Decreased

16. C. Components of Y Y = Ys + Yp+ Ym Ys = osmotic potential Yp = pressure potential Ym= matric potential

17. 1. Ys = osmotic potential a. Osmotic potential is a measure of the effect that solutes have on water potential. b. Pure water has an osmotic potential of zero. c. Adding solutes decreases the osmotic potential because water interacts with solutes. (more solutes = more negative) d. Thus Ysis always negative (if solute is present)

18. 2. Yp = pressure potential a. A measure of the effect that pressure has on water potential. b. Pressure can be positive (when something is compressed). Pushing c. Pressure can be negative (when something is stretched or pulled). Called tension. d. Water can handle large amounts of tension because of cohesion – the tendency of water to stick to itself (H bonding)

19. Figure 3.1

20. 3. Ym= matric potential a. Matric potential is a measure of water’s adhesion to non-dissolved but hydrophilic structures such as cell walls, membranes, soil particles etc. b. Adhesion can only decrease water’s free energy. c. So matric potential is always negative

21. Water moves from regions of high Ψ (less negative) to regions of lower Ψ (more negative). Why would water move to where it is less free? • Water acts to dilute, hydrate, decrease tension • i.e. water acts to stabilize water potentials • If two Ψ’s are equal, no net movement of water

22. Examples • Ψ = +46MPa Ψ = -22MPa • Ψ = -15MPa Ψ = -300MPa

23. Fig 36.8

24. D. Cells, Water Y, Terms 1. A flaccid cell (Yp = 0). No pressure is being exerted against the inside of the cell wall. Cell is not firm. Why? Solute concentration within the cell is lower than surroundings. Water leaves the cell. 2. A turgid cell (Yp = +) is filled with water, exerting pressure against its cell walls. Cell is firm. Why? Solute concentration within the cell is higher than surroundings. Water moves into the cell.

25. E. Terms for cells and water movement 1. Hypotonic solution – low solute concentration 2. Hypertonic solution – high solute concentration 3. A flaccid cell placed in a hypotonic solution will? 4. A turgid cell placed in a hypertonic solution will? This causes the cell membrane to shrink away from the cell wall (i.e. plasmolyze).

26. Fig 36.9a

27. Fig 36.9b

28. IV. Cell to Cell Transport • A. Three routes for lateral transport: • 1. Trans-membrane – water & solutes move • across the plasma membranes and cell walls of • adjacent cells • 2. Symplast – movement through a continuum of • cytoplasm connected by the plasmodesmata of cell • walls. • 3. Apoplast – extracellular pathway; movement • through the continuous matrix of cell walls

29. Fig 36.8

30. 4. Examples of Short Distance Transport a. Guard Cells • i. Mechanism: Opening • K+ is pumped into GC by active transport. Proton • pump creates membrane potential that drives K+ in. • Thus Ψ inside cell is lower than outside cell. • Water diffuses into the guard cell. • Sunlight, circadian rhythms, & low CO2 • concentration in leaf air spaces stimulate the proton • pumps & thus stomatal opening

31. ii. Mechanism: Closing Proton pumps no longer active (darkness) K+ is lost from the GC, creating lower water potential outside cell. Water flows out of GC and cells become flaccid Stomatal closure during the day stimulated by water stress – not enough water to keep GCs turgid

32. Fig 36.15

33. b. Motor Cells i. Description Leaves of these plants can flex & fold in response to stimuli Motor cells are the “joints” where this flexing occurs. Accumulate or expel potassium to adjust their Ψ & thus turgidity. ii. Examples: Venus’ flytrap Oxalis – leaves fold in sunlight to minimize transpiration; open in shade Transpiration = loss of water vapor from the stomata

34. http://www.uccs.edu/~ppbotany/Colo_family/Oxalid/oxalis_stricta_P.htmhttp://www.uccs.edu/~ppbotany/Colo_family/Oxalid/oxalis_stricta_P.htm

36. c. Transfer Cells i. Description Cell walls have many finger–like projections on the inner surface. The plasma membrane is pressed firmly against these convolutions, creating an increase in surface area Greater surface area means more molecular pumps & thus high – volume solute transport Found in areas of rapid, high volume transport: salt- excreting glands, sugar loading into phloem

37. d. Root Cells i. Description Soil particles coated with water, minerals; adhere to hydrophyllic epidermal cells of root hair Soil solution moves freely through epidermal cells & cortex via symplast and apoplast pathways Endodermis – selective barrier to soil solution between cortex & stele. Sealed together by the waxy Casparian strip (Suberin) – forces soil solution in apoplast to pass through the selectively permeable membrane of the endodermis. Once through the endodermis, soil solution freely enters the xylem

38. Fig 36.9 Suberin

40. V. Long Distance Transport Xylem: Transpiration (evaporation from leaves) creates a tension which pulls sap up from the roots, in direction of lower Ψ. Phloem: Hydrostatic pressure at one end of the sieve tube forces sap to the other end of the tube (= bulk flow).

41. A. Xylem Transport = sap 1. Forces for Xylem sap both pushed & pulled up the stem WHY? a. Root Pressure Stele has high concentration of minerals, decreasing Ψ. Water flows in, creating pushing pressure b. Guttation – exudation of water droplets by leaves during the night when transpiration is low. Caused by root pressure

43. c. Cohesion/Adhesion i. Transpiration – cohesion – tension mechanism ii.Transpirationalpull: Ψ of air typically << than Ψ of leaf, thus evaporation. iii. Water remaining in leaf is tightly adhered to cell walls in the mesophyll iv. This adhesion & surface tension of the water creates negativepressure – the pulling force

44. Figure 36.14

45. d. Aided by: i. Cohesiveness of water – allows water to be pulled up in a continuous column without breaking ii. Adhesion of water to hydrophyllic cell walls of the xylem, creates tension (negative pressure/ pull) iii. Diameters of tracheids & vessel elements are small, so lots of surface area for adhesion iv. Since movement is by bulk flow (i.e. no membranes to pass through), Ψs is not involved in the overall process

46. Fig 36.15

47. 2. Speed of Xylem Sap Translocation • ExamplesMax. Speed (cm/hr) • Conifers 120 • Angiosperm Trees 600 - 4400 • Herbs 6,000 • Vines 15,000 (0.6 mi/hr)

48. Why is xylem transport in trees much slower than in herbs? • 3. Forces that act against transpirational pull: • A. Gravity • B. Hydraulic resistance

49. 4. Control of Transpiration • a. Guard cells! – balance two contrasting needs of the • plant: • i. Conserve water • ii. CO2for photosynthesis • b. Water Use Efficiency (WUE) = g H2O lost / g CO2 • assimilated by photosynthesis average = 600/1

50. c. Adaptations by Desert plants to increase • their WUE: • i. Small thick leaves (less SA for water loss) • ii. Thick cuticle • iii. Stomata only on bottom of leaves • iv. High-volume water storage (cacti) • v.CrassulaceanAcid Metabolism (CAM) – plants • take in CO2 only at night, so that stomata only have • to be open at night.