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 The Effects of Temperature and Body
Size on Poikilothermic Metabolism
An illustration of the Q10 concept
Organisms and Temperature
•  Poikilothermy-temperature conforming animals
– Source of heat is the environment
– Body temperature is the ambient temperature
•  Ectothermy-preferred to term to poikilothermy
– Heliothermic: from the sun
– Thigmiothermic: from the substratum or medium
•  Endothermy-source of heat is the chemical
reactions within the organism
Temperature and Environment •  Temperature has a major
impact of water chemistry
•  The rate of chemical reactions
correlates with temperature
–  Increased temperature means
increased chemical reaction
(which means increased
biological activity)
Temperature, Metabolism and Q10
•  Complex mathematical models (Arrhenius equation) do
not take into account catalyzed reactions and that high
temperatures denature proteins.
•  Enzyme kinetics must be taken into consideration when
addressing the effects of temperature on metabolism.
•  To by-pass complex
mathematical equations,
Q10 was developed as a
descriptive model for catalyzed
reactions.
Defining Q10
•  There is a positive relationship between ambient
temperature and metabolic rate for ectotherms as
measured by changing oxygen consumption rates.
•  If Q10= 1, then the process is not temperature
dependent.
•  If a physiological process has a Q10= 2 then with every
10°C increase in temperature, there will be a doubling of
the rate of that process (or 10°C decrease leading to a
halving of the process).
•  Most enzymes (and therefore enzyme mediated processes
such as metabolism) have Q10 values ranging from 2 to 3.
⎛ k1 ⎞
Q10 = ⎜⎜ ⎟⎟
⎝ k 2 ⎠
10
( t 2 −t1 )
Oxygen Consumption
•  Methods to estimate metabolic rate depend on the
stoichiometric relationship between oxygen consumption,
carbon dioxide production, and ATP generation, which is
summarized by the equation for cellular respiration:
6O2+ 6C6H12O6→6CO2+ 6H2O + 36 ATP
•  Depending on the organism involved, one typically measures
either oxygen consumption or carbon dioxide production.
•  Metabolic rates of aquatic organisms are generally monitored
by following the rate at which oxygen is consumed (mg or ml
or Mol of O2/body weight/unit time).
Determining Metabolic Rate
•  Metabolic rates of aquatic organisms are generally
monitored by following the rate at which oxygen is
consumed (mg or ml or Mol of O2/body weight/unit
time).
mL O2
mg O2 consumed hour
=
grams hour ( weight of crayfish ) × (1.43)
Details about the Experiment
•  Find ambient temperature
–  set water bath 10°C above
•  Weigh organisms
•  Ambient (low temperature)
–  Aerate 15 minutes
–  Seal with watch glass
•  High Temperature
–  Aerate 15 minutes, equilibrate flask to high temperature
–  Seal with watch glasss
–  SEE FOLLOWING SLIDES FOR METHODS