1. Activity of Water Plant Physiology UNI Spring 2006

2. Overview Physical activity of water –Effect of temperature –Effect of pressure Chemical activity of water –Includes physical effects (T, P) –Also other effects Combining to get water potential

3. Physical activity of water Molecules have energy Molecules move around air water

4. Temperature effect Absolute zero Cold Medium Hot

5. Absolute Zero air water NO MOVEMENT

6. Cold Temperature air water SLOW MOVEMENT

7. Medium Temperature air water MEDIUM MOVEMENT

8. Hot Temperature air water FAST MOVEMENT

9. Effect of Pressure Low pressure Medium pressure High pressure PPP

10. Low Pressure air water SLOW MOVEMENT P

11. Medium Pressure air water MEDIUM MOVEMENT P

12. High Pressure air water FAST MOVEMENT P

13. To increase or decrease activity Increase or decrease pressure Increase or decrease temperature

14. Chemical activity of molecules Based on physical environment (T, P) Also based on chemical environment –Determines what a molecule interacts with –Determines the effect of the interactions

15. Physical and chemical effects Molecules have physical activity Also chemical activity –Interact with other chemicals –Each molecule behaves in its own way Water acts like water Ca acts like Ca –What affects the chemical activity? –How much?

16. Without solutes air water WATER MOLECULE NOT TIED DOWN BY SOLUTES STANDARD WATER ACTIVITY

17. + ++ + _ _ _ Add solutes air water SLOWER MOVEMENT WATER MOLECULE PARTLY COVERED WATER ACTIVITY IS LOWER

18. To decrease water activity Decrease temperature or pressure And…Tie the water up chemically –Add solutes –Water partly busy with solutes –Not fully free to act like water –Lower chemical activity

19. Change Water Activity Increase – temperature – pressure Decrease – temperature – pressure –add solutes More solutes = more effect

20. Pure Water, Standard T, P air water WATER ACTIVITY OF PURE WATER = STANDARD STANDARD = 0 THIS WATER ACTIVITY = 0 COMPARE ALL WATER TO THIS STANDARD

21. Water Potential Water activity of your solution compared to water activity of standard solution Standard solution = 0 Your solution can be –Same activity (WP = 0) –Lower activity (WP < 0) –Higher activity (WP > 0) Doesnt occur in biology

22. Need to get some numbers Water potential scale Like temperature scale

23. Absolute & Relative Scales: Temperature

24. Relative Scales: Water Potential

25. Water potential scale The water in a cell (beaker, bucket, trunk) –Not the other chemicals Distributed characteristic (all the same) –Like temperature Compared to standard (0) Can be positive, zero or negative Expresses effect of P, T, solutes –On water, compared to standard

26. Summary Physical activity of water molecules changes with –Temperature, pressure Chemical activity of water molecules changes with solutes Water potential tells us the total activity –Compared to pure water, standard TP WP can be +, 0, -