2. AP Biology 2006-2007 Transport in Plants

3. AP Biology Transport in plants  H 2 O & minerals  transport in xylem  transpiration  evaporation, adhesion & cohesion  negative pressure  Sugars  transport in phloem  bulk flow  Calvin cycle in leaves loads sucrose into phloem  positive pressure  Gas exchange  photosynthesis  CO 2 in; O 2 out  stomates  respiration  O 2 in; CO 2 out  roots exchange gases within air spaces in soil Why does over-watering kill a plant?

4. AP Biology Ascent of xylem fluid - overview  Transpiration: loss of water vapor from leaves pulls water from roots (transpirational pull); cohesion and adhesion of water  Root pressure: at night (low transpiration), roots cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; guttation

5. AP Biology Ascent of xylem fluid Transpiration pull generated by leaf

6. AP Biology Water & mineral absorption  Water absorption from soil  osmosis  aquaporins  Mineral absorption  active transport  proton pumps  active transport of H + H2OH2O root hair aquaporin proton pumps

7. AP Biology Mineral absorption  Proton pumps  active transport of H + ions out of cell  chemiosmosis  H + gradient  creates membrane potential  difference in charge  drives cation uptake  creates gradient  cotransport of other solutes against their gradient

8. AP Biology Root anatomy - Water Flow dicotmonocot

9. AP Biology Endodermis & Casparian strip

10. AP Biology Two Routes  Symplast route (lateral)  cytoplasmic continuum  Apoplast route (lateral)  continuum of cell walls

11. AP Biology Water flow through root  Porous cell wall  water can flow through cell wall route & not enter cells  plant needs to force water into cells Casparian strip

12. AP Biology Controlling the route of water in root  Endodermis  cell layer surrounding vascular cylinder of root  lined with impermeable Casparian strip  forces fluid through selective cell membrane  filtered & forced into xylem cells

13. AP Biology Mycorrhizae increase absorption  Symbiotic relationship between fungi & plant  symbiotic fungi greatly increases surface area for absorption of water & minerals  increases volume of soil reached by plant  increases transport to host plant

14. AP Biology Mycorrhizae

15. AP Biology Transport of sugars in phloem  Loading of sucrose into phloem  flow through cells via plasmodesmata  proton pumps  cotransport of sucrose into cells down proton gradient

16. AP Biology On a plant … What ’ s a source … What ’ s a sink? can flow 1m/hr Pressure flow in phloem  Mass flow hypothesis  “source to sink” flow  direction of transport in phloem is dependent on plant’s needs  phloem loading  active transport of sucrose into phloem  increased sucrose concentration decreases H 2 O potential  water flows in from xylem cells  increase in pressure due to increase in H 2 O causes flow

17. AP Biology Experimentation  Testing pressure flow hypothesis  using aphids to measure sap flow & sugar concentration along plant stem

18. AP Biology Maple sugaring

19. AP Biology 2006-2007 Don’t get mad… Get answers!! Ask Questions!

20. AP Biology 2006-2007 Ghosts of Lectures Past (storage)

21. AP Biology Chloroplasts Epidermal cell Nucleus Guard cell Thickened inner cell wall (rigid) Stoma openStoma closed H2OH2O water moves into guard cells H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Control of Stomates K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ K+K+ water moves out of guard cells  Uptake of K + ions by guard cells  proton pumps  water enters by osmosis  guard cells become turgid  Loss of K + ions by guard cells  water leaves by osmosis  guard cells become flaccid

22. AP Biology Control of transpiration  Balancing stomate function  always a compromise between photosynthesis & transpiration  leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO 2 for photosynthesis