Bio 543

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  1. Reynolds number (Re)
    • way to characterize a moving fluid as it interacts with an object (organism)
    • dimensionless number (no units)
    • ratio of relative importance of inertial to viscous forces (high Re=effct of viscosity is mall relative to momentrum of fluid)
    • ***high means less "sticky"
  2. Re is a rough indicator of ____
    the relative importance of inertial vs viscous forces-eg. what is important is numbers >>1 vs numbers <1, not subtle differences in values of R
  3. Humans live in a high Re world
    Inertia (numerator) dominates
  4. In contranst , tiny planton in water
    viscous forces (denominator) dominate
  5. Really weird things happen at Re<1
    • "rakes act like paddles(like using a fork to grab a bread crumb out of honey)
    • "Kung-Fu Fighting (push son fluid, and is relative far away)
  6. Take home points for Boundary layers
    • 1. Boundary layers are the regions where organisms interact with the rest of the world:
    • obtain food, oxygen and dissolved nutrients
    • plants obtain CO2 (for photosynthesis) and eliminate excess oxygen ( in high light)
    • disperse gametes, larvae and get rid of sediments
    • Lose water and lose or gain heat
    • 2. shape of organism, and height above the bottom, affects the characteristics of the momentum of the boundary layer. Shape of organism, and height above the bottom, affects the characteristics of the overlying boundary layer
    • 3. We can broadly characterize this interaction of flow and organism with a Reynolds number (Re)
  7. Trade-offs in evolutionary pressure
    Fluid flow
    • affects the exchange of heat, mass and momentum
    • Difficult to adapt to one requirement without affectiong others
    • For example, shapes that maximize mixing of fluid (for increased gas exchange,etc) also increase drag
  8. Trade-offs in evolutionary pressures
    • this means that it is very difficult for one shape to be optimal for all environmental "challenges"
    • organisms are seldom "perfectly designed" for their environments, in large part because of these trade-offs
    • eg structures that maximize oxygen uptake also maximize water---->lungs
  9. Enotherms
    • Metabolic heat is of prime importance and can be used (to varying degress) to compensate for changes in external environment
    • ***Endoderms also exchange heat with their environment
    • Tachymetabolic- fast metabolism for given size (Tall people have fast metabolism)
  10. Poikilothermic ectotherms
    • "cold blooded"
    • most reptiles,insects, etc
    • body temp largely driven by solar radiation
    • (in the Poles its cold)
  11. Homeothermic endotherms
    • mamals, birds
    • (having a home is a warm feeling)
  12. Heterothermy
    • some animals are both poikilothermic and homeothermic
    • For example, bats and small birds (with high SA/V) are homeothermic when active and poikilothermic when they sleep. This is temporal heterothermy
  13. Partial endothermy
    newborns-high SA/V and are very reliant on external condtions (eg nest temperature, heat from parent)
  14. Inertial Homeothermy
    large or small organisms?
    • =Gigantothermy
    • Large organisms with low SA/V
    • even though metabolic rate is small, SA where heat escapes is even smaller
    • =effect of thermal inertia
    • large reptiles stay warm at night and cool during the day
  15. Facultative endothermy
    • can turn on and off heat production (form of termporal heterothermy)
    • for example bumblebees--every morining rapidly beat wings to heat up until body temp increaes; can't fly until they do
    • Note that these are ectothermic animals
  16. Regional heterothermy
    • =regional endothermy
    • some organims maintian different temperatures in different "zones" of the body
    • Eg tail of tuna is heated, allowing for higher metabolic rate

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Bio 543
2010-09-11 14:52:23

BIO 543
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