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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