Lecture 04 Water Relationships

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Lecture 04Water Relationships
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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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• Solutions
• Solutes dissolved substances
• Osmosis movement of water across cell membrane
• Osmotic potential tendency of solution to
  attract water from high to low concentration
• due to dissolved substances higher conc.
  dissolved substances lower tendency to loose
  water ? lower osmotic potential
• Semipermeable the capacity (of a cell membrane)
  to restrict passage of certain substances
• important in maintaining appropriate
  concentration of water/dissolved substances
  within a cell or organism

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• In solutions
• Hyperosmotic or Hypertonic more dissolved
  substances outside cell
• water leaves the cell ? crenation (like a
  pickle)
• 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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• 1. An organism from a freshwater lake has been
  placed in the ocean. It has been placed in an
  environment with a (greater or lesser?)
  concentration of solutes or a (hyper-osmotic or
  hypo-osmotic?) environment.
• 2. If the solute concentration of the tissues of
  an organism are greater than that of the
  surrounding environment it will tend to (loose or
  gain?) water.
• An organism living in a tide pool subject to
  considerable evaporation will likely experience
  increasingly ____________ conditions during an
  extreme low tide and thus must have mechanisms to
  prevent excess water __________ during that time.

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• Water/salt balance in animals
• Kidneys regulation function
• Terrestrial animals produce hypertonic urine
• Animals that drink salt water? special salt
  secreting glands
• Freshwater animals produce hypotonic urine
• Saltwater animals hypertonic urine secrete
  excess salt via gills

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• Moisture in the atmosphere
• Relative humidity - amount of water vapor in air
  relative to the amount it can actually hold at
  that temperature
• Affects living things through evaporation
• RH water vapor density
• saturation water vapor density (X
  100)
• Absolute humidity the amount of water vapor in
  the atmosphere expressed as a percent by volume

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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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• In what environments would you expect to find
  organisms with the most elaborate adaptations
  preventing evaporative water loss?
• What kind of adaptations would decrease
  evaporative water loss
• in plants?
• in animals?
• In animals which cannot sweat what behaviors are
  associated with evaporative cooling?

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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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• If absolute humidity stays the same but the
  temperature drops what typically happens?
• Why do fogs form so frequently along the central
  and northern California coasts during the summer?

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• Water and Plants
• Earliest plant lived in moist habitats
• No vascular system
• Unprotected gametes require moisture film
• Higher plants adaptations to varied habitats
• Protected gamete
• Roots and vascular system

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• Soil Water Relations (see pages 29-30)
• Water binds to surface of soil particles
  (adhesion)
• matric potential
• Soil particle size impacts amount of water
  present and how tightly it is bound
• Clay lt 0.002mm
• Silt 0.002 ? 0.05 mm
• Sand gt 0.05mm
• Which of these would hold more water?
• Which would hold water more tightly?
• Space between particles pore space
• Cohesion (capillary forces) holds water in pore
  space
• Field Capacity pore space filled, water held by
  capillary forces against gravity

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• What forces must plant roots overcome in order to
  remove water from soil?
• 1. Matric potential
• 2. Osmotic potential
• Water potential matric osmotic potential
• Would a dry soil would have a lower or higher
  water potential than that same soil would at
  field capacity?
• In terms of matric and osmotic potential, what
  happens when a plant wilts?

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

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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