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Water Relationships

Water Relationships. 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

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Water Relationships

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  1. Water Relationships

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. Evaporative Water Loss

  7. 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

  8. 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.

  9. 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

  10. 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

  11. 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

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

  13. 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

  14. 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 • > 90% of water taken in by roots is lost to the atmosphere • Adaptations include reduced leaf area, modifications to leaf surface

  15. 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

  16. Guard cells turgid Guard cells flaccid

  17. Water Regulation on Land - Plants

  18. Plant adaptations: • Root system development • Low growth habit (reduced wind exposure) • Hirsute leaves • Leaf coloration

  19. 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.

  20. 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

  21. Water Regulation on Land - Animals

  22. 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

  23. Osmoregulation in Animals • Osmoregulation is the regulation of the body’s osmotic (water and salt) composition • Adaptation to dry terrestrial habitats: produce hypertonic urine • Insects: Malpighian tubules Active transport ofK+, water is drawn osmotically, reabsorbtion in the hindgut • Vertebrates: Kidneys • Hydrostatic filtration (blood under pressure) • Selective reabsorption • Mammals, birds produce hypertonic urine

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

  25. 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

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