bio 543 IV

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Author:
lin3
ID:
34115
Filename:
bio 543 IV
Updated:
2010-09-11 19:44:08
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bio IV
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bio 543 IV
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  1. Cold Tolerance
    3 primary Stategies
    •1. Freeze Avoidance

    • •2. Supercooling (For organisms that are freeze intolerant= very specialized
    • kind of freeze avoidance)

    •3. Freeze Tolerance
  2. Whis is freezing Lethal?
    •Body (and cells) are mostly made of water: 50-70%

    • •When ice forms, it can rupture cell membranes
    • (crystallization)

    • •Also, removes water from cells (dehydrates them) forming
    • toxic levels of minerals that are left behind

    •For some organisms, enzyme failure
  3. How does freezing occur?
    • •When temperature drops below freezing point, nucleation occurs and ice
    • crystals form- sort of a chain reaction

    • Freezing point
    • depends on solute concentration: more solutes, freezing point is lowered (stays
    • liquid at lower temperatures
  4. Freezing
    • •Freezing involves a certain amount of “chance”- once
    • nucleation (“seeding” occurs, it spreads

    • •Thus, staying dry on surface can prevent internal
    • freezing (=innoculative freezing)

    • •Larger organisms have a greater chance of freezing than
    • smaller organisms
  5. Freeze Avoidance
    • •Hibernate in areas below the frost line or in
    • microhabitats that don’t freeze
  6. Supercooling
    • •Animals would die if they froze- cell membranes would
    • fracture
    • •Maintain fluids at an unfrozen state below the freezing
    • equilibrium point
    • •Involves exclusion of nucleating agents
  7. Supercooling organisms
    •Live with their body fluids well below 0°C

    • •Takes advantage of concept that fluids can dip well below freezing point without actually
    • solidifying

    •Water can be supercooled to -40°C as long as it is completely free of contaminants

    • •Can also add antifreeze
    • compounds-
    • commonly glycerol

    •Antifreeze peptides-prevent ice crystals from forming
  8. Freeze Tolerance
    • •Often involves:
    • • ice nucleating proteins: controls ice formation so that it occurs outside of
    • cells (Extracellular)
    • •Cryoprotectants: assures that only a
    • limited amount of body water freezes (slows chain reaction)
  9. Wood Frogs
    • •Mobilizes glucose
    • when freezing first begins (from liver to bloodstream)- allows ice to form more
    • slowly)
    • •Intentionally dehydrates- shunts water out of cells into coelomic tissues

    • •Freezing needs to
    • start at relatively high tissues, before supercooling starts, otherwise freezing will occur too rapidly and
    • animal will die
  10. Freeze tolerance often involves
    • • ice nucleating proteins: controls ice formation so that it occurs outside of
    • cells (Extracellular)

    • Cryoprotectants: assures that only a
    • limited amount of body water freezes (slows chain reaction
  11. Tend to see freeze tolerance in places where freezes are___-
    • are predictable and prolonged
    • Freeze intolerence (avoidance or supercooling) in places where freezing is unpredictable-can rapidly switch back and forth

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