1 Water Relations Chapter 6

2 Outline (I) Water Movement in Terrestrial Environments (II) Water Movement in Aquatic Environments (III) Water Regulation on Land (IV) Water and Salt Balance in Aquatic Environments

3 (I) Water Movement in Terrestrial Environments Relative Humidity: Water Vapor Density Saturation Water Vapor Density (x 100) Water vapor density is measured as the water vapor per unit volume of air. Saturation water vapor density is measured as the quantity of water vapor air can potentially hold.  Changes with temperature.

4 (I) Water Movement in Terrestrial Environments Total Atmospheric Pressure  Pressure exerted by all gases in the air. Water Vapor Pressure  Partial pressure due to water vapor. Saturation Water Vapor Pressure  Pressure exerted by water vapor in air saturated by water. Vapor Pressure Deficit  Difference between WVP and SWVP at a particular temperature.

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6 Evaporative Water Loss

7 (II) Water Movement in Aquatic Environments If two environments differ in water or salt concentrations, substances will tend to move down their concentration gradients.  Diffusion  Osmosis: Diffusion through a semipermeable membrane.

8 (II) Water Movement in Aquatic Environment Isomotic: Body fluids and external fluid are at the same concentration. Hypoosmotic: Body fluids are at a higher concentration than the external environment. Hyperosmotic: Body fluids are at a lower concentration than the external environment.

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10 (III) Water Regulation on Land Terrestrial organisms face (2) major challenges:  Evaporative loss to environment.  Reduced access to replacement water.

11 Water Regulation on Land - Plants

12 Water Regulation on Land - Plants W ip = W r + W a - W t - W s W ip = Plant’s internal water W r =Roots W a = Air W t = Transpiration W s = Secretions

13 Water Acquisition by Plants Extent of plant root development often reflects differences in water availability.  Deeper roots often help plants in dry environments extract water from deep within the soil profile. ..

14 Allocation of carbon to root tissues Peppermint

15 Water Conservation by Plants Many terrestrial organisms equipped with waterproof outer covering. Behavioral modifications to avoid stress times. Drop leaves in response to drought. Thick leaves Few stomata Periodic dormancy

16 當葉水勢能超過臨界值，植物關閉氣 孔以節約水，光合作用便下降. (Oak 較耐乾旱 )

17 Water Regulation on Land - Animals

18 Water Regulation on Land - Animals W ia = W d + W f + W a - W e - W s W ia = Animal’s internal water W d = Drinking W f = Food W a = Absorbed by air W e = Evaporation W s = Secretion / Excretion

19 Water Acquisition by Animals Most terrestrial animals satisfy their water needs via eating and drinking.  Can also be gained via metabolism through oxidation of glucose:  C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O  Metabolic water refers to the water released during cellular respiration.

20 Water regulation of terrestrial animals

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24 Dissimilar Organisms with Similar Approaches to Desert Life

25 Two Arthropods with Opposite Approaches to Desert Life

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30 (IV) Water and Salt Balance in Aquatic Environments

31 (IV) Water and Salt Balance in Aquatic Environments

32 The End

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