1. Chapter 5 Water relations
Life on earth linked closely with water

2. Metabolic rate and salt concentration in body fluids
Ionic concentrations affect shape of enzymes (performance)
Loss of enzyme function = ?
Water uptake, loss, active transport of water

3. Water movement = high concentration to low concentration
Or, low salt concentration to high salt concentration

4. Measuring Water Gradients In Terrestrial Environments
Water Vapor Pressure: Amount of atmospheric pressure due to water molecules
Vapor density = g water / m3 air
Relative Humidity
100 x Actual vapor density / Saturation Water Content

5. Water content of air Water vapor Relative humidity = Changes with T
water vapor density
saturation water vapor density
Changes with T
warm air can hold more water

6. Fig 6.2

7. So what?
At saturation vapor pressure, water precipitates from air as fast as it is evaporated

8. The effect?
Greater difference between saturation vapor pressure and actual vapor pressure:
= more rapidly water will evaporate
This term = vapor pressure deficit

9. Fig 6.3

10. Terrestrial environments have high variation in water:
Temporal variation mainly seasonal
Solar warming and evaporation

11. Terrestrial environments have high variation in water:
Hadley cells
Tropical rainforests tend to be equatorial
Deserts tend to be ~ 30˚

12. Spatial variation due to:
Oceans, mountains, prevailing winds
Environmental T
Topographic position + draining
Soil type = water retention by roots

13. Terrestrial organisms:
Regulate water by balancing acquisition with losses
Consumption, root uptake
Evaporation, excretion, transpiration

14. Warm/hot terrestrial environ:
Many species evaporate water

15. Aquatic environments
Water availability based on water potential gradient
Body fluid to environment

16. Water moves from high to low potential
Water concentration gradient
Water into roots - soil particles
Up stem = xylem tube
Evaporates out of leaves (vpd)
Fig 6.5

17. Freshwater environments:
Environment has higher water potential (lower salt concentration)
Freshwater organisms are hyper-osmotic
Organisms tend to gain water and lose salts

18. Freshwater environments:
Adaptations?
Use energy to take-up salts
Excrete large amounts dilute urine

19. Freshwater fish + inverts
Hyperosmotic => tend to gain water, lose salts
In gills, cells absorb NaCl
Kidneys produce much dilute urine

20. Energy
Expended
Fig 6.28

21. Marine environments:
Environment has lower water potential (higher salt concentration)
Organisms tend to lose water and gain salts = hypo-osmotic
Adaptations?
Drink much, use energy to excrete salts, excrete little and concentrated urine

22. Marine fish + inverts Hypo-osmotic = lose water, gain salts
Drink seawater
Gill cells secrete NaCl
Kidneys produce concentrated urine

23. Isosmotic marine organisms:
Same concentration inside as outside
Sharks, many marine invert’s (e.g., crabs, shrimps)

24. Fig 6.4

25. Case history: desert beetle p. 133
Water budget
Water intake = 50 mg/g body mass per day
40 mg from fog
1.7 mg from food
8.4 mg from metabolic water

26. Fig 6.8

27. Tiger beetles in Arizona
One species adjacent to streams
Another in dry grasslands
How much water is lost through cuticle by each?
Lab chamber
(30 C , dry)

28. Fig 6.15
Cuticle is more waterproof

29. less
= more lipids + wax

30. Fig 6.14

31. Fig 6.25

32. Cicadas can evaporate water to cool their body
In lab chamber - T = 45.5 C
Body T = 42.5 C
When relative humidity = 100 %
Body T = 45.5 C
When relative humidity = 0 %
Body T = 41.5 C

33. Fig 6.22

34. Root growth and water Grassland plants in western Canada
Fringed sage
Moist microclimate =
Lower root biomass
Higher aboveground biomass

35. Fig silver sage

37. The End