Chapter 7 ENERGY METABOLISM

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review questions

  1. Animals and Thermodynamics
    1. Animals consume energy containing materials (nutrients) to replace energy that is lost when moved through systems.
    2. Animals must obey the laws of thermodynamics
  2. Energy Metabolism
    1. Law of Entropy (2nd Law of Thermodynamics)
      1. all metabolic processes involve a loss of free energy (organized energy --> disorganized energy)
      2. All energy involved in metabolism is eventually lost in the form of heat
  3. Figure 7.2 The uses of energy by an animal
    1. Measuring heat production (Box 7.2)
      1. 1 calorie = 4.186 Joules
      2. C6H12O6 + 6O2 ---> 6CO2 + 6H2O + 2820 kJ/molecule
    2. Metabolic Rate: energy metabolism (use) per unit time
      1. Calorimeter
    3. Method 1: Direct Calorimetry
      1. Lavoisier's direct calorimeter
      2. Latent Heat of Fusion
        1. It takes 80 calories to melt 1 g of ice
      3. Image from Wikipedia: "The world's first ice-calorimeter, used in the winter of 1782-83, by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were based on Joseph Black's prior discovery of latent heat. These experiments mark the foundation of thermochemistry."
    ice-calorimeter, used in 1782-83, by Lavoisier and Laplace
  4. Method 2: Indirect Calorimetry (Box 7.4): Respirometry
    1. Figure A:  closed respirometer
    2. Figure B:  open respirometer
    3. Different food contain different amounts of energy (Table 6.1)
  5. RQ = Respiratory exchange ratio (Table 7.2)
    1. Ratio of CO2 formed to O2 used
  6. Method 3
    1. CO2 production
  7. What Affects Metabolic Rate? (Table 7.3)
    1. Physical Activity
    2. Environmental Temperature
    3. Digestive Processing
    4. Body Size
    5. Age
    6. Gender
    7. Endocrine Activity
    8. Circadian Rhythms
    9. Aquatic Salinity (Osmoregulation)
  8. Terms
    1. Basal Metabolic Rate
    2. Standard metabolic Rate
    3. Activity metabolic rates
    4. Metabolic Scope
  9. Metabolic Rate (MR) and Body Size in Mammals
  10. Figure 7.6 The effect of body size on weekly food requirements in a mammal
  11. Figure 7.7 BMR as a function of body weight in various species of placental mammals
    1. Total MR rate does not increase linearly with mass
  12. The Scaling Exponent (b) Defines the Type of Scaling Relationship
    1. Y = aMb
    2. If b < 1, Y increases at a slower rate than X
      1. negative allometry
  13. Calculating Basal or Standard Metabolic Rate
    1. The relationship is allometric (linear on log axes)
  14. Figure 7.8 Weight-specific BMR as a function of body weight in various species of placental mammals
    1. The MR per unit body mass increases rapidly with decreasing body size.
  15. Figure 7.9 Weight-specific metabolic rate as a function of body weight in four groups of vertebrates
  16. Figure 7.10 Metabolic rate and body weight are related linearly on log-log coordinates
  17. For Mammals
    1. Total MR = VO2 = 0.676 * Mb0.75
    2. VO2/kg = 0.676 * Mb-0.25
  18. See review questions taken from taken from Animal Physiology -- Biology 462, University of Washington. Metabolism II -- Body Size, Endothermy vs. Ectothermy, R. B.Huey
    1. calculate the times for a 1g animal of each taxon to use 10 ml O2.  (If W=1g, then MR = 10 ml O2 = a*1b*t; t = 10/a)
    2. calculate the times for a 100 g animal of each taxon to use 10 ml O2.  (If W=100 g, then MR = 10 ml O2 = a*100b*t) 
  19. To illustrate the problems associated with extrapolations of drug dosing, consider the elephant, Tusko.
    1. Since an elephant  weighs approximately 1000 times as much as a cat, Tusko received approximately 1000 times more LSD than a cat (297 mg for the elephant, 0.26 mg for the cat)
    2. Based on the human dose
      1. 0.20 mg LSD / 70 kg human = 0.003 mg LSD/kg;
      2. 2970 kg elephant x 0.003 mg / kg = 8.9 mg LSD
    3. Cat metabolic rate is 0.53/0.09 = 6x that of an elephant; Dosage should be recalibrated to 297mg/6 = 50 mg LSD
    4. Human metabolic rate is 0.23/0.09 = 2.5x that of an elephant. Dosage should be recalibrated to 8.9/2.5 =  3.5 mg LSD
  20. See review questions for another question from Animal Physiology -- Biology 462, University of Washington. Metabolism II -- Body Size, Endothermy vs. Ectothermy, Raymond B.Huey
    1. Researchers had found that a daily dose of 500 mg acrylamide induces cancer in rats. What should we determine about risks to humans?
  21. Among other things, this relationship (MR = aMb) is important for calculating drug dosages.
  22. See review questions for a question on adult versus infant dose based on weight ant metabolic rate.
  23. Surface to volume ratio
    1. 2/3 and Rubner's Law
    2. Slope (b) of MR-mass equations ranges ~ 0.62 - 0.83
    3. Encompasses both 0.66 (2/3) and 0.75 (3/4)
    1. Kleiber's Law
      1. MR = 0.676 * Mb0.75
      2. Why is the exponent 0.75 instead of 0.67?

     

    Figure 1. Body size versus metabolic rate for a variety of species. From WikipediaOriginally published in Kleiber (1947).

     

  24. Figure 7.13 Two contemporary theories to explain the allometric relation between metabolic rate and body weight: A
    1. The Fractal model is that the metabolism scales (W0.75) from the fractal branching patterns of respiratory and circulatory systems that deliver oxygen and nutrients to tissues.
      1. The fractal branching pattern of these tubes impacts how resources are taken up, transported and transformed within the body
  25. Figure 7.13b: Two contemporary theories to explain the allometric relation between metabolic rate and body weight: B
    1. multiple causes theory states that the rate of any major processes depends on the interaction between multiple underlying processes
  26. Heart size and Heart rate? (Table 7.4, Fig. 7.11)
    1. heart rate is inversely related to body mass R = 243 Mb-0.25
  27. Heart size is proportional to body size
    1. However, smaller bodies have a higher MR
  28. Heartbeat Frequency
  29. physiological time
    1. for mammals metabolic time is proportional to mass0.25
    2. mammals usually get about 1-2 billion heartbeats, but for smaller animals, the beats go by faster, so they live shorter
    3. humans do better by a factor of 3
  30. Heart size and Heart ?
  31. Ecological consequences:
    1. Smaller species need more food per unit of body weight
    2. Smaller species draw more resources from the ecosystem
  32. Physiological and ecological implications of metabolic rate-body weight
    1. Cellular properties differ allometrically, particularly in reference to density of mitochondria.
  33. Ecological Consequences
    1. The structure of ecosystems is affected by allometric relations. (see fig. 7.6)
    2. Ex: a square kilometer can support 95kg of warthogs, or 460kg of zebras, or 1250kgs of elephants.
    3. In calculating the carrying capacity of an area, both number and size of animals must be taken into account.

       

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