Water Relationships

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Water Relationships
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Outline

• 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
• Water moves from greater to lesser concentration
• Relative concentrations of water
• In air relative humidity
• In water osmolarity or salinity
• Balance of water gain and loss impacts survival
  of organisms in a particular environment.

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• Evaporation Loss of Water from Organism to
  Atmosphere
• Important for terrestrial organisms
• Provides cooling
• Represents major loss of water.
• Greatest in dry climates water vapor in air
  less where humidity is lower
• Concentration gradient greater
• Cooling from evaporation greatest in dry climates.

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• Dry Environment
• Great water pressure deficit
• High saturated vapor pressure (air could hold a
  lot of water)
• Low actual vapor pressure
• Greater movement of water from organism to
  environment

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Evaporative Water Loss
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• Dew
• Condensation of water on surfaces cooled by
  radiation of heat to atmosphere
• Impacted by absolute humidity amount of water
  vapor in atmosphere
• Fog Forms at dew point on nucleation sites,
  small particles
• Important source of moisture in summer along
  California coast some other dry environments

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• Water Movement in Aquatic Environments
• Water moves down concentration gradient by
  diffusion.
• 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
• Osmosis special case of diffusion - water
  movement across a membrane.

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• Water concentration in solutions
• Osmolarity a measure of concentration of
  dissolved substances in water
• Salinity concentration of dissolved salts - salt
  water solution contains relatively less water
  than fresh water
• That means ?
• Water moves from area of less dissolved salts to
  more dissolved salts

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• Concentration of solutes and cells
• Hyperosmotic or Hypertonic more dissolved
  substances outside cell like a pickle
• water leaves the cell ? crenation
• Hypoosmotic or Hypotonic less dissolved
  substances outside
• water enters the cell ? cell swells and bursts
• Isoosmotic or Isotonic same concentration
  inside and out, the cell is at dynamic
  equilibrium

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• Organisms must maintain cellular/tissue
  osmolarity within narrow limits
• Osmoregulation
• Adapted to particular osmotic environment
• Generally water moves in and out of cells freely
• Salt movement is restricted due to charged nature
  of salt ions

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• Water and Creatures in Terrestrial Environments
• Terrestrial organisms face (2) major challenges
• Evaporative loss to environment.
• Reduced access to replacement water.

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• Water and Plants
• Earliest plant lived in moist habitats
• No means to transport water within structure
• Required moisture film for reproductive processes
• Later plants developed vascular system
• Movement by transpiration

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• Water moves from soil to top of plant in unbroken
  stream
• Transpiration provides the pull
• Rate of transpiration is regulated by action of
  guard cells
• gt 90 of water taken in by roots is lost to the
  atmosphere
• Adaptations include reduced leaf area,
  modifications to leaf surface

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Dermal Tissue

• The epidermis of a plant is often covered with a
  thick waxy layer called the cuticle

• Guard cells
• Paired cells with openings between them (stomata)
• Allow gas exchange

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Guard cells turgid
Guard cells flaccid
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Water Regulation on Land - Plants
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• Plant adaptations
• Root system development
• Low growth habit (reduced wind exposure)
• Hirsute leaves
• Leaf coloration

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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.
• Park found supportive evidence via studies
  conducted on common Japanese grasses, Digitaria
  adscendens and Eleusine indica.

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Water Regulation on Land - Animals

• Wia Wd Wf Wa - We - Ws
• Wia Animals 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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• Physiological Regulation of Tissue-Water Balance
  in Animals
• Kidneys evolved to produce hypertonic uring in
  terrestrial organisms
• Other mechanisms exist as well eg. Certain sea
  birds

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Osmoregulation in Animals

• Osmoregulation is the regulation of the bodys
  osmotic (water and salt) composition
• Adaptation to dry terrestrial habitats produce
  hypertonic urine
• Insects Malpighian tubules Active transport of
  K, water is drawn osmotically, reabsorbtion in
  the hindgut
• Vertebrates Kidneys
• Hydrostatic filtration (blood under pressure)
• Selective reabsorption
• Mammals, birds produce hypertonic urine

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• Marine birds (Procellarids) minimize water loss
  by excreting salt through specialized glands
• Additional water is absorbed in the cloaca

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• Water Summary
• Number of unique properties due to chemical
  nature
• Concentration of water drops as percent salt in
  solution rises
• Movement of water from greater to lesser
  concentrations occurs by specialized diffusion
  osmosis
• Development of various strategies to deal with
  water has lead to patterns of distribution of
  species of plants and animals