Chapter 5 Water relations

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Chapter 5 Water relations

• Life on earth linked closely with water

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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

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Water movement high concentration to low
concentration

• Or, low salt concentration to high salt
  concentration

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Measuring Water GradientsIn 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

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Water content of air
Water vapor Relative humidity water vapor
density saturation water vapor density Changes
with T warm air can hold more water
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Fig 6.2
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So what?

• At saturation vapor pressure, water precipitates
  from air as fast as it is evaporated

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The effect?

• Greater difference between saturation vapor
  pressure and actual vapor pressure
• more rapidly water will evaporate
• This term vapor pressure deficit

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Fig 6.3
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Terrestrial environments have high variation in
water

• Temporal variation mainly seasonal
• Solar warming and evaporation

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Terrestrial environments have high variation in
water

• Hadley cells
• Tropical rainforests tend to be equatorial
• Deserts tend to be 30

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Spatial variation due to

• Oceans, mountains, prevailing winds
• Environmental T
• Topographic position draining
• Soil type water retention by roots

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Terrestrial organisms

• Regulate water by balancing acquisition with
  losses
• Consumption, root uptake
• Evaporation, excretion, transpiration

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Warm/hot terrestrial environ

• Many species evaporate water

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Aquatic environments

• Water availability based on water potential
  gradient
• Body fluid to environment

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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
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Freshwater environments

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

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Freshwater environments

• Adaptations?
• Use energy to take-up salts
• Excrete large amounts dilute urine

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Freshwater fish inverts

• Hyperosmotic gt tend to gain water, lose salts
• In gills, cells absorb NaCl
• Kidneys produce much dilute urine

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Energy Expended
Fig 6.28
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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

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Marine fish inverts

• Hypo-osmotic lose water, gain salts
• Drink seawater
• Gill cells secrete NaCl
• Kidneys produce concentrated urine

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Isosmotic marine organisms

• Same concentration inside as outside
• Sharks, many marine inverts (e.g., crabs,
  shrimps)

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Fig 6.4
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Case history desert beetlep. 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

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Fig 6.8
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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)

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Fig 6.15
Cuticle is more waterproof
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less
more lipids wax
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Fig 6.14
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Fig 6.25
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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

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Fig 6.22
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Root growth and water

• Grassland plants in western Canada
• Fringed sage
• Moist microclimate
• Lower root biomass
• Higher aboveground biomass

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Fig 6.11 - silver sage
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The End