Transcript Water Vapor Density

Water Relations
Chapter 6
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Outline
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Water Availability
Water Content of Air
Water Movement in Aquatic Environments
Water Movement Between Soils and Plants
Water Regulation on Land
Water Acquisition by Animals
Water Acquisition by Plants
Water Conservation by Plants and Animals
Water and Salt Balance in Aquatic
Environments
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Water Availability
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The tendency of water to move down
concentration gradients, and the magnitude
of those gradients, determine whether an
organism tends to lose or gain water from its
environment.
 Must consider an organism’s microclimate
in order to understand its water relations.
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Water Content of Air
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Evaporation accounts for much of water lost
by terrestrial organisms.
 As water vapor in the air increases, the
water concentration gradient from
organisms to air is reduced, thus
evaporative loss is decreased.
 Evaporative coolers work best in dry
climates.
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Water Content of Air
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Relative Humidity:
Water Vapor Density
Saturation Water Vapor Density
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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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Water Content of Air
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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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Water Movement in Aquatic Environments
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Water moves down concentration gradient.
 Water is more concentrated in freshwater
environments than in the oceans.
Aquatic organisms can be viewed as an
aqueous solution bounded by a selectively
permeable membrane floating in an another
aqueous solution.
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Water Movement in Aquatic Environments
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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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Water Movement in Aquatic Environment
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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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Water Movement in Aquatic Environment
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Water Movement Between Soils and Plants
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Water moving between soil and plants flows
down a water potential gradient.
Water potential (Ψ) is the capacity to
perform work.
 Dependent on free energy content.
 Pure Water ψ = 0.
 Ψ in nature generally negative.
 Ψsolute measures the reduction in Ψ due
to dissolved substances.
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Water Movement Between Soils and Plants
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Water Movement Between Soils and Plants
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Ψplant = Ψsolute + Ψmatric + Ψpressure
Matric Forces: Water’s tendency to adhere
to container walls.
 Ψpressure is the reduction in water potential
due to negative pressure created by water
evaporating from leaves.
 As long as Ψplant < Ψsoil, water flows from
the soil to the plant.
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Water Regulation on Land
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Terrestrial organisms face (2) major
challenges:
 Evaporative loss to environment.
 Reduced access to replacement water.
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Water Regulation on Land - Animals
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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 Regulation on Land - Animals
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Water Regulation on Land - Plants
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Wip= Wr + Wa - Wt - Ws
Wip= Plant’s internal water
Wr =Roots
Wa = Air
Wt = Transpiration
Ws = Secretions
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Water Regulation on Land - Plants
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Water Acquisition by Animals
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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 Acquisition by Plants
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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.
 Park found supportive evidence via
studies conducted on common
Japanese grasses, Digitaria
adscendens and Eleusine indica.
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Water Conservation by Plants and Animals
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Many terrestrial organisms equipped with
waterproof outer covering.
Concentrated urine / feces.
Condensing water vapor in breath.
Behavioral modifications to avoid stress
times.
Drop leaves in response to drought.
Thick leaves
Few stomata
Periodic dormancy
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Dissimilar Organisms with Similar
Approaches to Desert Life
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Camels
 Can withstand water loss up to 20%.
 Face into sun to reduce exposure.
 Thick hair: Increased body temperature
lowers heat gradient.
Saguaro Cactus
 Trunk / arms act as water storage organs.
 Dense network of shallow roots.
 Reduces evaporative loss.
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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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Scorpions
 Slow down, conserve, and stay out of sun.
 Long-lived
 Low metabolic rates
Cicadas (Diceroprocta apache)
 Active on hottest days.
 Perch on branch tips (cooler microclimates).
 Reduce abdomen temp by feeding on xylem
fluid of pinyon pine trees.
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Water and Salt Balance in Aquatic Environments
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Marine Fish and Invertebrates
 Isomotic organisms do not have to expend
energy overcoming osmotic gradient.
 Sharks, skates, rays - Elevate blood
solute concentrations hyperosmotic to
seawater.
 Slowly gain water osmotically.
 Marine bony fish are strongly
hypoosmotic, thus need to drink
seawater for salt influx.
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Osmoregulation by Marine Organisms
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Water and Salt Balance in Aquatic Environments
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Freshwater Fish and Invertebrates
 Hyperosmotic organisms that excrete
excess internal water via large amounts of
dilute urine.
 Replace salts by absorbing sodium and
chloride at base of gill filaments and by
ingesting food.
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Osmoregulation by Freshwater Organisms
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Review
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Water Availability
Water Content of Air
Water Movement in Aquatic Environments
Water Movement Between Soils and Plants
Water Regulation on Land
Water Acquisition by Animals
Water Acquisition by Plants
Water Conservation by Plants and Animals
Water and Salt Balance in Aquatic
Environments
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