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Water Relations

Chapter 6

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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

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(I) Water Movement in Terrestrial Environments

• Relative Humidity:

Water Vapor DensitySaturation 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.

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(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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Evaporative Water Loss

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(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.

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(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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(III) Water Regulation on Land

• Terrestrial organisms face (2) major challenges: Evaporative loss to environment. Reduced access to replacement water.

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Water Regulation on Land - Plants

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Water Regulation on Land - Plants

• Wip= Wr + Wa - Wt - Ws

• Wip= Plant’s internal water• Wr =Roots• Wa = Air• Wt = Transpiration• Ws = Secretions

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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.

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• Allocation of carbon to root tissues

Peppermint

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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

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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 )

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Water Regulation on Land - Animals

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Water Regulation on Land - Animals

• Wia= Wd + Wf + Wa - We - Ws

• Wia= Animal’s internal water• Wd = Drinking• Wf = Food• Wa = Absorbed by air• We = Evaporation• Ws = Secretion / Excretion

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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: C6H12O6 + 6O2 6CO2 + 6H2O

Metabolic water refers to the water released during cellular respiration.

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Water regulation of terrestrial animals

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Dissimilar Organisms with Similar Approaches to Desert Life

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Two Arthropods with Opposite Approaches to Desert Life

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(IV) Water and Salt Balance in Aquatic Environments

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(IV) Water and Salt Balance in Aquatic Environments

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• The End

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